ive noticed on my wrx when i plant my foot down sometimes the engine judders , it feels like its misfiring, whats causing this? could it be ignition leads?

 

what year is it? if its an older wrx and uses coilpacks then it could be that these are beginning to break down, usually resulting in a slight missfire higher up the rev range. Quite common.

 

its a 2001 m8.

 

sorry to use your thread but I am experiencing a similar problem with my MY99 impreza. boost is normally around 17 PSI and when I plant my foot I get a slight juddder like a misfire but no knock registered on the knocklink.
This evening the boost was cut to 7 PSI which I assume is limp home mode but no ECU light has come on. Shouldn't be a fuel problem as I only use optimax or tesco 99. Is the coil situation where I should start as it is going for a service in the next three weeks plus MOT on Wednesday this week.
Any advice much appreciated,
thanks

Richard

 

In this case I would check either 2 things, the maf which is a known weakness on this year of car, or the actuator rod on the turbo, these can sometimes come off resulting in low boost.

 

Is there any loss of power, does it cut out? or does it just feel like it is misfiring?

 

when the accelerator is pressed it initially feels like a judder but there is no knock indicated. On the way home this evening I was enjoying the car!!! and the boost came on and only went up to 7 PSI so there is no cut it appears to have gone into limp home mode but there is no engine light on the dash which is strange. The boost still goes upto 7 PSI in each gear but the idle is steady with no fluctuation up and down, just steady around 750 rpm so I don't suspect the MAF plus the engine stalls as sson as the MAF is disconnected. Usualy get some knock if the MAF goes and the engine is quiet in that sense. Engine sounds fine the actuator rod does not appear to be disconnected. Still no check engine light beyond the normal illumination on startup.
May see if the car is happier tomorrow morning.
Where would I get a coil and how much should this be the case?

 

i think it might be the spark plugs or leads..

 

would check all hose connections to and from the turbo, also may be worthwhile cleaning the boost solenoid.