Jerky at 2500rpm only sometimes

[r4itei]

like the title says, sometimes i start it and everything is peachy. sometimes it takes a few minutes of being jerky at 2500 rpm. when it gets jerky, i clutch in, let the car roll a bit, shift into a higher gear and wait til it reaches 2500. after the 5 or so minutes, everything is perfect throughout the whole powerband.

i'm not sure if jerky is a descriptive enough word. it kinda surges, or bucks... cant think of any other words to describe.

any ideas? im thinking maybe dirty injectors?

[Garfinkles Motor Works]

Is the car stock with a stock computor if not what has been done ?

[r4itei]

AFAIK, it's got a PFS exhaust, stock intake replaced by a short ram intake. cooling system has been upgraded to a koyo rad, it's got an FMIC.

computer is stock, i believe. i will ask previous owner to be sure.

[dexspeed]

Hmmm. I had a similar problem with an old E30 BMW. It turned out to be as simple as a clogged fuel filter. I'd start there as that's easy enough to do and does not take much time, then maybe start looking for vacuum leaks.

[SINxSELEKTAH]

Fuel filters are the kind of thing that are rarely changed and always ignored.

[Speed of Light]

A worn O2 sensor can cause this problem too--the reason for this is that the ecu will set fuel trims based on what the O2 sensor reports as stoichiometric during closed loop operation. If the reported value is in error, all of the ecu's fuel maps will reflect that error, which may make the afr's marginal under some conditions.

No doubt the intake and exhaust mods have also affected the volumetric efficiency of the engine which requires compensation as well.

Hope this helps.

[jkstill]

As you see a number of issues can cause this.

For me it was TPS (Throttle Position Sensor) adjustment.

It was a different car after adjusting the TPS - no bucking at all.