Scoobypedia | Trusted knowledge for everything Subaru
Scoobypedia | Trusted knowledge for everything Subaru
Search Scoobypedia:

Scoobypedia Home

The Knowledge

Buying Guides

Projects

Scoobypedia

edit sidebar

Common problems, symptoms and remedies

Thankfully, the Impreza is one of those cars with almost no major problems, and reliability on the whole is excellent. There are however, a few relatively minor problems, which affect specific models. These are shown briefly in the table below, and discussed in more detail later on.

FaultSymptomsModels Affected
Blow-off valve (Dump Valve, Air bypass valve)Loud noise between 2-4000 rpm which sounds like someone blowing over top of a bottle.1997/1998 Turbo
Waste GateSolenoid can be noisy (clicking), and in extreme circumstances can cause sudden loss of power when accelerating hardAll Turbo
Heat ShieldNoise from engine compartment caused by cracked heat shield.1994-6 Turbos
Interior MirrorInterior mirror vibrates lightly, blurring rearward visionAll
ClutchClutch judders when moving off. Worse when coldAll Turbo
BrakesSpongy brakesAll models
Radio resettingRadio resets when wash/wipe or electric windows activatedAll 5-door
Brake PipesNoise from engine compartment caused by brake pipes resonating against bulkhead1998 Turbo
Porous 15" wheelsLoss of tyre pressure1994-7 Turbo
ECU bug :-)Jerk when throttling off from full boost1994-6 Turbo
EngineEngine splutters to a halt. Caused by driver enjoying him/herself so much they fail to notice they were running low on fuel :-)All Imprezas
Worn anti-roll bar bushesClonking noise from suspensionWRXs
ABS isn't magicUnexpected activation / long stopping distancesAll ABS cars
Use of low octane fuel?Serious engine damage (melted pistons)STi (4 & 5?)
Piston SlapNoisy (chattery) engine when starting from cold1998/99 models

Dump Valves

There seems to be a recognised problem with the 1997 specification car's dump valve (aka Blow off Valves and By-pass Valves). This does not shut properly under boost and thus vibrates giving the sound similar to someone blowing across the top of an open bottle. It has also been likened to a steam train whistle or ship fog horn in extreme circumstances!. Meanwhile the 1998 model seems to have a totally revamped and larger blow off system, but I have had reports that the problem sometimes still occurs.

Waste gate solenoid

The 1997 specification lowered the turbo boost pressure from 1.0 bar to 0.9 bar. The engine breather system vents into the air intake and it is possible for the oil and condensing, burnt oil vapours build up in this valve. This valve is a safety device for detecting overboost and will cause fuel and ignition to be cut if it senses that 1.2bar (97/98 models) has been reached. If it is bunged up, it isn't sensing correctly and will shut down the engine under high boost conditions. The solution advised by Subaru France was not to fill the oil up to maximum but to leave it at half filled only.

If your wastegate solenoid does pack up, the fix is to pull the T shaped supply hose off and fill it with brake cleaner from an aerosol. Then go for a blast before the cleaner evaporates. Tippex thinners also do the job. '98 models have a revised part, which is three port sensing and there have been no reported failures. You can get '97 cars upgraded.

Apparently the fault often occurs just after a service when the oil level may be slightly too high. The 1998 specification engine apparently has revised sensing locations, to over come the above problems but there have been some reports of failure on early '98s.

Sometimes this fault is incorrectly termed as "over boosting". The sensor is designed to detect an over boost situation and is usually so sensitive in normal operation that 1.19bar = ok and 1.20bar = fuel cut routine due to over boost. When it becomes contaminated by oil, this is lost and the sensor can cut in at much lower boost values, cutting in the routine under normal hard acceleration. The effect of this routine is quite disconcerting as all engine power is suddenly lost with some drivers reporting it feeling as if they have just driven into a brick wall!

How Things Work

Differences between waste gate and dump valve:

The waste gate is on the exhaust side of the turbo, the dump valve is on the intake side. This is what they do:

When you take your foot off the throttle to slow down or change gear a flap called the "butterfly" closes and stops the flow of air into the engine. The turbo though will still be spinning and thus tries to pump air in, but cannot and rapidly slows down with the restricted air flow. When you reapply the throttle the butterfly is opened and the restriction is removed and the turbo can again increase in rpm to develop boost. The time taken to re-gain turbo impeller rpm is felt as turbo lag and in the situation above, would be quite crude (early 911T). What a dump valve does is allow the pressurised air to vent, either to atmosphere, or back through the intake plenum (a recirculating system - as per Impreza). This reduces the restriction on the turbo impeller allowing it to spin almost freely and therefore retain momentum. If you then re-apply the accelerator soon after (such as during a gear change) the butterfly opens and dump valve closes and the turbo still spinning at quite a high speed. It takes much less time to spin up to full boost and thus creates less lag. If the dump valve should leak it will not allow full boost to be applied to the engine. This is the steam train whistle effect.

The dump valve is also called a blow off valve and air by-pass valve.

When the pressure sensors start saying that enough is enough, the wastegate opens to allow exhaust gas to by-pass the turbo and exit straight into the exhaust system. This reduces the load driving the turbo and lowers the boost of the charge going in.

A Turbo anti lag system works by allowing fuel and air into the engine, when the throttle is not depressed. This passes through the chamber, but explodes on contact with the hot exhaust manifold (typically 800C). This explosion then drives the turbo impeller, maintaining a very high rate of spin.

There are two down sides to anti lag systems; apart from the noise, 1) the car never actually stops pulling, which could be a bit disconcerting, 2) exhaust manifold and turbo temperatures can rise to over 1100C and this temperature and pressure mean that they last for about 1000 miles.

Exhaust manifold heat shield

Heat shields were a common fault on pre-'97 cars, as these cars do not have the tray under the engine bay. It is possible for road water to splash the very hot shields caused them to fracture. They then resonate, as the two sides of the crack vibrate together. This is a warranty fix, but if it's the one where the left and right side pipes join, (by far the most common one to fail - this is a very hot area) then the dealer should pack the lower shield out by 3mm. This lowers the temperature of the shield and it will then last much longer, if not forever. The owner who came up with the 3mm spacer trick had got through 3 shields in 15,000 miles and was used to driving a car that buzzed. It has never failed since.

Interior mirror

Blurred vision due to vibrations of the mirror. An owner submits the following suggestion if your dealer doesn't know how:

  1. Remove the plastic cover which sits ,over the roof to mirror
  2. mounting screws , Small screw drive required for this to gently "flip" it off.
  3. Remove all three of the mounting screws to release the mirror arm from the roof.
  4. Remove the central screw holding the plastic spacer onto the mirror arm mount .
  5. Super glue the spacer back onto the arm and quickly refit the central screw , nice and tight but not enough to crack it .
  6. Refit the mirror back onto the roof mount with the three screws , again quite tight.
  7. Leave this fully to dry , 24HRs is best .
  8. Now fully test will a fast motorway drive and you will find the vibration has disappeared!

Clutch judder

... when cold

This is caused by the material used to with stand the abuse given to it by owners.....usually ok when warmed up. Can also be caused by problems (wear/dirt ?) with the special platinum spark plugs used in the Impreza. Replacing these at the 15,000/30,000 mile service can cure the problem (although sometimes only for a month or so!).

Another suggestion has been to treat your Impreza to several full bore standing starts (when warm of course), which apparently helps clean up the surfaces of clutch components.

For 1998 models, and some 1999 models, there have actually been many cases of faults with the standard clutch system. The symptoms are progressively worsening juddering when cold, leading to severe clutch judder at all times. Subaru dealers (certainly in the UK), have been replacing these faulty clutches free of charge under warranty, including a new flywheel, as long as the mileage isn't well above average, and the problem is severe enough. Some owners report a slight juddering at times, but this is not enough to warrant a new clutch.

... when hot

Can be cured by uprating the clutch fluid to a DOT 5 fluid. Caused by fluid getting too hot from the engine bay heat. See also above for clutch problems with 98/99 cars

Brakes

The standard brakes (pre-99) are not great, suffering from a soft spongy pedal and being somewhat prone to fade under moderately hard use. Consider braided hoses, and replace fluid frequently - ideally with a DOT5 such as Castrol Response. Better brake pads can make a big difference to pedal feel, braking response and resistance to fade. See the BRAKES section for more information.

Note that the Mintex and (to a lesser extent) Pagid pads are quite a bit "dirtier" than the standard pad, leaving a lot more brake dust on the wheels. The Mintex pads are also notoriously squeaky!

It has also been known for some time, that under hard braking, the blukhead actually flexes, resulting in a spongier pedal feel. This can be significantly reduced by fitting a special bracket designed to reduce this flex. This is in an inexpensive item, and is available from a variety of suppliers such as MRT, Scoobymania and Power Engineering.

US expert Mike Shields of SPD Tuning Service writes about brakes ...

"A braided-steel brake line kit will noticeably harden up the pedal during the high brake line pressure caused by hard use with hard pads. Going down the road everyday, you may not notice they are there. The braided hose does not expand with high line pressure and will tend to not cut or tear away should something bad happen at track day, still leaving you with brakes for the other three corners of the car should one corner get crushed. Not a good thought, but a very important consideration. I have seen whole suspension corners hanging by the steel braided brake line after a shunt.The real source of the soft brake pedal on the Impreza RS (is it the same with the turbo?) is the vacuum booster design, which uses a dual stage booster. As the pedal is depressed, the first vacuum chamber assists the pedal effort. Once the pedal is down about 1/2 inch, the rod of the booster assembly uncovers a second port, adding the second chamber vacuum assist to the first.So, while the unassisted brake pedal pressure is now quite high, this second stage keeps the pedal at your foot quite soft with the brakes on hard. The purpose of this dual stage booster is simply to keep the driving effort of the car low because the majority of commuters prefer it that way.The soft pedal makes it somewhat hard for the average driver to "heel and toe" at high speeds and cornering forces. This is the main source of the complaint. You will become a smoother driver if you have a proper driving seat and the operating force of the brake pedal is a firmer than the standard RS design. Here is why this is true.While your body is slamming around at or above one "G" (So that is where those coffee stains are on the passenger door panel came from! (True story, btw, from the cup holder in the center of the dash to the door panel, with none on the floor - great turn-in!)) it becomes difficult to hold your foot at just the pressure you want on the brake pedal and still give the throttle the stabs it needs to select the next lower gear smoothly. The harder pedal gives a better feel by opening up the total range of pressure felt and by making this range of actuation pressure correspond to the actual braking force of the car.A second source of soft brake pedal is brake fade. Actually heat. Well actually, the gasses that the pads give off when stinking hot. They form a boundary layer on the rotor surface and no matter now hard you push, the car stops poorly. Everyone knows that drilled brake rotors help, right? SPD Tuning Service does not sell drilled brake rotors, so what is the deal?A clever dude in England involved with world rally racing asked a simple question just a couple of years ago. Since we can't use carbon/carbon brakes due to the rules and if brakes fade due to gas coming off the pad, why drill rotors to make room for the gases when you can make a pad that does not give off gas in the first place? Mintex 1155 compound pads are a development of this concept suitable for every day road use. The pad is made and then "cooked" in an oven so hot that the gasses in the pad material actually cook off. This is a somewhat expensive (and slow) process. The gasses have to be recovered (keep it Green, please) and the pads must be properly heat cycled to retain their other desirable properties. Note also the STI Ver 5 298mm rotor kit pads have this feature also.The end result is a pad with four very desirable features: 1) extreme fade resistance, 2) long pad life, 3) no "bedding in" needed and 4) they work when cold. The Mintex 1155 pads do not develop a soft pedal until MUCH higher brake temperatures are reached. This greatly increases the percentage time you can be on the brakes hard, such as seen on "track days" or in descents from mountain passes. And you do not need drilled rotors! The standard vented rotors just fine, and there is no risk of developing stress cracks from often seen on drilled rotors. A special SPD Tuning Service tip: Never come to a stop with stinking hot brakes and especially sit with your foot on the pedal at even a stop sign, much less a red light. The rotors will be cooling off rapidly except for the areas under the pads, and the rotors will warp. In turn, never make a banzai stop from above 70mph with cold brakes, unless you have to. The rotors will warp. They will especially have this tendency when they are older and thinner, than when they are new. Older can be 10,000 miles or 70,000 miles. Usually, the rotors become sensitive to the effects of high performance use when you are past half way through your second set of pads. They are thinner than they were when new.Under hard use they will eventually warp and/or develop a case of the "wides". This is where the rotor metal has worn down and the rotor surface is so uneven that the rotor is thicker in some areas than others. As you come to a stop under moderate pedal pressure, they can drag lightly as the thicker portion of the rotor goes past the pads. If not warped severely, you can turn (true the surface of) the rotors, but depending on the severity of use, the smart money says it is time for new rotors, especially if on the second set of pads. They often are just used up and will warp again. There is actually a minimum width for the rotors cast into the part to help you with this decision.Long pad life. For some it will be from 40,000 miles to 60,000 miles. For others, long pad life is from 2500 smiles increased to 5000 smiles. It just depends on how hard and how often you are on the brakes. The Mintex pads are harder and they also wear longer. As a result, wear the rotor metal at a seemingly higher rate. The higher metal wear rate is a characteristic of the pad compound AND they way they tend to be used by their owners! With standard pads, if you do not mind the risk of a bit of brake squeak, it is OK just to put in a set of pads without turning the rotors. With Mintex or other "hard" compound pads, especially when used hard, it is important to true up the rotors when changing pads.The Mintex 1155 compound does not need bedded in. Bedding in is actually the thermal cycling of the pad material more than some idea of wearing the pad to the rotor surface. With a new car (pay attention here!) it is very easy to go out an romp on the brakes and heat glaze the surface of the stock pads. The car will have a hard brake pedal and will have poor stopping distances as a result. Because the Mintex 1155 compound has been thermally cycled during the "de-gassing" process, they are ready for prime time out of the box. Just a few good hot passes and they are as good as they are going to get.They work when cold. Unlike true racing pads, the 1155 compound Mintex pads are designed to operate at a lower and wider temperature range. They will actually stop the car when the brakes are cold. It is a standing joke that many people have purchased racing pads for their street car only, at a minimum, to scare themselves half to death on the freeway the first time they need all the brakes after driving in a straight line for 15 minutes. Racing pads have no grip when cold! A semi-trailer truck with 40,000 pounds on board will out brake you for the first two stops from 70mph. Of course, you will stop about 1000 feet shorter on the third stop, but that is not the point. It is that first stop that counted. Please do not use racing compound pads on the street. The 1155 compound is the practical limit.What if you still get brake fade and the soft pedal blues? You have two choices, use the brakes less, (which may make your lap times faster, not slower), or get bigger brakes. The fronts do most all the stopping, so it is standard practice to install larger front brakes on road cars and leave the rears for later. Larger brakes are usually needed when the power goes up. The car will get to higher speeds between each corner and need the extra heat dissipation of larger and larger brakes. Then again, some of us just like the big stopping power from high speeds that larger brakes will give you. It is just part of the total performance envelope."

Radio resetting

There have been several reports of the radio resetting or locking itself up on 5 door models. Two owners have seen this when the rear wash/wipe is activated. Two others have had the radio cut out on one speaker when the rear electric window behind the driver is operated. A mod is apparently available from Subaru involving putting a diode across the relay but it has also been reported that this fix did not work! In both cases turning the radio off and then on again cured the problem.

Brake Pipes

There has been one incident to date of a strange mechanical noise coming from the engine compartment. It apparently sounded like a top-end engine noise, but was eventually traced to the brake pipes being too close to the bulkhead above the pedals. At certain revs, the resonating pipes vibrated loudly against the bulkhead. The problem was cured by gently easing the pipes away from the bulkhead.

Porous 15" Wheels

Some of the 15" alloy wheels on 1994-7 turbos were slightly porous, resulting in tyre pressure loss similar to a slow puncture. (A dealer also reports some early Speedlines suffering the same problem). The warranty remedy requires your wheels to be repaired, which - since it can take months - can be a bit inconvenient ...

ECU bug

In a low gear at high boost, such as pulling on to a roundabout in 1st or overtaking in 3rd, even a tiny reduction in throttle results in a sudden jerk, far worse than you'd expect from totally releasing the throttle, and enough in some cars to cause the inertia-seatbelts to activate. You'd expect the dump valve to open and to get smooth deceleration from engine braking, but instead you have to be very gentle with the pedal.

Apparently it's better on 1997/8 cars, but still present to an extent.

There is also an apparent protection system built in to the ECU to prevent damage to the gearbox under hard acceleration in 2nd gear. When travelling at a constant speed for a period of time between 3,000 and 4,000 rpm(more than 5 seconds), pressing the accelerator can result in less than full boost being delivered until 5,000+ rpm is reached. This phenomenon has been observed in a variety of cars, in different countries, but only by a small handful of drivers. Without replacing the ECU with an aftermarket one, the only real alternative is to make a change in your driving style. Simply drive along in 3rd gear, and change down to 2nd when needed, or simply change up to third and let the mid range torque do all the work.

Worn anti-roll bar bushes

WRXs seem prone to wear of the anti-roll bar bushes, leading to a clonking noise. The bushes (and the mounts if necessary) need to be replaced. Harder, "rally type" or "powerflex" bushes can be fitted but all the bushes would have to be changed at once, and the ride of the car can be noticably harsher.

ABS Isn't Magic

Not a fault with the Impreza or its brakes (obviously), but many owners don't appreciate the limitations of an anti-lock braking system.

ABS prevents wheels from locking under braking, because a sliding wheel has no grip (of course!). Having no grip means stopping distances are increased, and steering response is lost. ABS works by sensing when a wheel is about to lock and momentarily releasing the brake, just as in the conventional technique of "cadence braking", but performed many times each second. While a driver performing cadence braking applies and releases the brakes on all wheels together, depending on the complexity of the ABS, either all 4 brakes can be controlled independently ("4-channel": expensive and rare), or the brakes on each axle are activated as a pair ("2-channel"). The pre-98 Impeza has 3-channel ABS, allowing the front brakes to be controlled separately but with the rears worked together. The 98 Impreza got 4-channel ABS.

In the early days of ABS, an exceptional driver on a non-ABS car could stop shorter by holding the wheels just on the point of locking, and thus achieve maximum traction for the whole of the stop. Modern ABS has improved to the level where virtually no driver can beat it.

There are situations where ABS makes things worse. On a loose surface such as snow or gravel, a locked wheel builds up a wedge which slows the car better than ABS. Also when the road drops away - over a crest or following a bump or into a sunken manhole cover - the unweighting of the wheel means that even a moderate braking force can lock the wheel, activating the ABS. It's often a surprise when this happens!

Use of low octane fuel

We have heard a small, but still alarming, number of reports of serious engine damage to recent STi cars which have been run on low octane (95 RON - regular unleaded in the UK) involving damaged pistons. We don't have enough information to say for sure, but things are certainly pointing that way. We recommend against prolonged running of these highly tuned engines on regular unleaded. Use 97 RON if you can, and use a good quality octane booster for extended hard use such as track days, especially in hot weather. If you own one of these vehicles, then it would be sensible to invest in a device known as a "Knocklink" which detects knock and displays visually knocking/pinking/pinging/detonation. which may not be audible over the engine noise. These can be obtained from a number of suppliers here in the UK, and overseas.

Piston Slap

It seems a small percentage of the MY98 cars have had problems with Piston Slap after a period of 10,000 to 20,000 miles has been covered. This manifests itself as a knocking noise which is much more pronounced when the engine is cold. This should not be confused with a ticking/tappet type noise which is common on all Impreza engines , but a distinct knocking noise which is most noticed between 1,500 and 2,000 rpm. In the UK, Subaru have been resolving the problems by fitting an a completely new short engine (block, crank, pistons) , and this cures the problem completely. Some cars are apparently much worse than others, with very lightly driven cars being just as susceptible as those driven hard! All Subaru dealers should be aware of this problem, and offer to resolve (free of charge under warranty) if the problem exists. If your dealer denies all knowledge, then go to another dealer who may be more sympathetic to your cause. The work takes between 2 to 3 days to perform, and as well as running it in again, you most get your ownership document(s) updated with the new engine number. If the problem occurs on a normally aspirated engine, then a simple piston replacement can be used, instead of a whole new block.

<< Starting And Stopping Engine | SIDC FAQ | Modifications >>

Copyright 1998-2000 Steve Breen, Peter Croney, Adam Curtin, John Stewart, see Copyright page for details

Page last modified on August 30, 2007, at 09:04 AM
Scoobypedia can not be held responsibile for the information published here. Site rules apply for all published content.