My 2002 WRX wagon has slight, but annoying stuttering and hesitations at part throttle and full throttle between 2000 and 3500 RPMs. It has good power and smoothness at high revs.

I was wondering if that was normal (the dealer said there was no problems with my car), but after reading one of the writeups in some mag about their WRX having a clogged injector at 12,000 miles, I figured my car could have an issue at 9000.

I put fuel injector cleaner in it and it smoothed out and ran like a champ with the hesitations being removed totally in the lower gears or muted to the point of not being much of an issue in gears 3 and 4.

But after that tank of gas, the car went back to it's previous hesitation with just normal 93 octane.

Has anyone else experienced this? Is this likely to be a clogged injector? Fouled plug? Is my ECU perhaps picking up engine knock and retarding timing at low RPMs (that the higher octane in the fuel injector cleaner is defeating)?

I want to do a Vishnu Stage Zero or SubZero in a couple of months, but want to iron out any issues before I add more stress to the system.

Is there a good way to test any of these hypotheses? (I know I can start by pulling plugs, but haven't had a free weekend yet...) I just put more fuel injector cleaner in it to see if the cycle repeats itself.

Thanks,
Craig

 

My 2003 (1,800 miles) has it also. No mods
I was considering the grounding mod to see if it would help.