April 20Apr 20 Hi all, I've bought an impreza from a friend that's got an issue, it's a low mileage standard bug eye wrx. it stood for a couple of years and it developed from there! It won't rev up from idle, it tries but it chuggs and backfires in the exhaust and inlet manifold. Now six years later it's time to repair the problem.I'm a time served mechanic and it's got me stumped, before I bought it it went to a garage for repair but they couldn't fix it either. I will list. New batteryNew timing beltNew plugsAll coils work ok and all 4 are brand new Replacement uppipe cat deleteRecon turboNew fuel filterNew fuel tank was drained New crank sensorNew cam sensor Brake servo vacuum capped off. New Denso maf/mas Removed the exhaust just in case it was blockedEcu replaced Fuel pressure at 40psiReturn fuel pressure 10psiAll cylinders are 140psiAll live readings look OK and no eml warnings.No air leaks, smoke tested. 40kpa on idle All injectors checked, Removed and testedRemoved and cleaned earth's Fuel trims are indicating running rich.I haven't removed the fuel pump to check the tea bag filter but I've got 40psi at the engine. What am I missing?
April 21Apr 21 You seemed to have approached it in the right sequence and covering all the bases - The areas of concern I was thinking of you have already listed:Removed the exhaust just in case it was blockedNo air leaks, smoke tested. 40kpa on idleFundamentally, the engine requires air to enter and exit from the cylinders, the above have always been the culprit in similar situations (Mondeo's used to suffer from the Cat breaking up and the 'brick' dropping down which restricted the flow and wouldn't rev up)Air leaks are common in this situation as well but if you are not seeing smoke then there are no leaks present.If the engine is sound, e.g. valve timing, etc then I'm stumped as well - but if it went to a garage beforehand and they may have changed a setting or two then I would be tempted to return it to stock settings as much as possible and go from there.Please do let us know what you find
April 30Apr 30 have you checked out the throttle position sensor?what spark plugs went in it?Has it got fresh fuel in it?have you done an ecu reset?
May 4May 4 Author On 4/30/2026 at 1:58 PM, Tidgy said:have you checked out the throttle position sensor?what spark plugs went in it?Has it got fresh fuel in it?have you done an ecu reset?Hi NGK, new fuel and I replaced the ecu. Kind regards.
May 4May 4 Author On 4/21/2026 at 8:52 AM, SOC Admin said:You seemed to have approached it in the right sequence and covering all the bases - The areas of concern I was thinking of you have already listed:Removed the exhaust just in case it was blockedNo air leaks, smoke tested. 40kpa on idleFundamentally, the engine requires air to enter and exit from the cylinders, the above have always been the culprit in similar situations (Mondeo's used to suffer from the Cat breaking up and the 'brick' dropping down which restricted the flow and wouldn't rev up)Air leaks are common in this situation as well but if you are not seeing smoke then there are no leaks present.If the engine is sound, e.g. valve timing, etc then I'm stumped as well - but if it went to a garage beforehand and they may have changed a setting or two then I would be tempted to return it to stock settings as much as possible and go from there.Please do let us know what you findYeah I removed the o2 sensor and it was the same and I also undone the exhaust from the turbo but I'm still thinking it's the exhaust. The oil is filling with fuel so I recon it can't burn it.
May 5May 5 If the fuel is washing down into the bores and then diluting the oil I am guessing it may be a little on the overfuelling side of things...I have known a wiring loom chafing through the insulation and grounding an earth on an injector before - chance find really as it was over the gearbox.
May 5May 5 Author 4 hours ago, SOC Admin said:If the fuel is washing down into the bores and then diluting the oil I am guessing it may be a little on the overfuelling side of things...I have known a wiring loom chafing through the insulation and grounding an earth on an injector before - chance find really as it was over the gearbox.The issue only developed from standing for a couple of years but I will check! Wouldn't this show an error code?
May 6May 6 If the injectors are over-injecting and / or the spray pattern isn't as it should be (I know you said you replaced them) but once fitted its hard to see what is occurring under combustion pressures.
May 6May 6 Author Hi I removed them from the engine, tested using a brake clean Sprayer and a 12 volt supply, they all worked and didn't drip, not sure if the spray pattern was good or bad tbh! I was thinking of replacing them all four but I don't think it's the cause of my non rev up issue.
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