Philip_W

Not really a thread requesting info as such, more as a reference for me however if anyone has experienced the same please feel free to contribute.

Bought a 2003 WRX STi at the tail end of last year. Lightly modified with a JGM remap, turbo back exhaust system and I assume fuel pump although no paperwork to prove this.

​Within maybe a month of owning it I had a CEL which was a misfire code of P0302 and a rough idle.

Dealer took the car back after I had new spark plugs fitted and swapped coilpack around (issue remained). The car was taken to a reputable Subaru specialist. The car came back to me fixed but there was nothing conclusive that was pinned as 'the problem'.

A couple of months down the line and the code came back again, same code and a misfire on idle. At this point the dealer put me directly in touch with the specialist who offered some advice (they are some 120 miles away from me so I was working from their suggestions).

I cleaned the PCV, MAF, ICV etc which seemingly did nothing. Having done nothing with the injectors I ran a couple of tanks of fuel with some fuel system cleaner. At the same time I went on a trip to the Nurburgring. By the time I got to Dover (couple of hundred miles) the idle sorted itself out and the misfire code went and never came back again. This was in may.

Fast forward to Monday of last week. 50mph zone opening up into NSL, 6th gear and a gradual press of the throttle to increase speed to 60. The car coughed and immediately flashed the CEL. I pulled over and checked Torque app, suprise suprise P0302 has returned.

The car had a very definite misfire that is apparent on idle and when driving 'steady'. I haven't really driven the car since but when I did and accelerated the misfire seemed to go and the CEL disappeared from the dash.

I have swapped spark plugs and coilpack from Cylinder 2 to 1. No good. On pulling Cylinder 2 the spark plug was wet, it smelled of fuel so I assume it's not burning the fuel as it should, presumably due to the misfire.

I took Injectors 2 and 4 out, had them ultrasonically cleaned and put them back in opposite cylinders (2 in 4 and 4 in 2). Misfire still remains. Car does not appear to be kicking out smoke of any sort (no blue or white smoke visible to the eye anyway).

At this point there is little i can now do myself to investigate so the car is going to Chevron Motorsport tomorrow to try and get to the bottom of it. I haven't dealt with them previously but from reading feedback on here it seems they know what they are doing.

Can anyone offer any light on the potential cause? I am now thinking it may possibly be something more sinister like an actual mechanical fault within the engine. I suppose a compression and leakdown test will tell us more.

Phil