engine jerks and sounds like a missfire
 

Hi, long time reader short time poster (uasly have all my answers found in later posts). i have been experiencing a jutter commig from my engine when i rev between 2k -4k rpms. its kinda strange cus it dosent happen 100% all of the time. when it does happen it dont matter if its warm or hot (i never tap the gas when its cold so i wouldent know if it happends when cold but never happends when engine doing warmup prep). its feels like the engine is missfiering but it jerks/pops at the same intervals when at 2k to 4k rpms (like every 1.5 seconds). also it will do it right when i tap the gass, (most of the time) but not when i let off it. ive checked the TPS and it is ok and idles w/out a slight hicup. everything is stock and ive checked most of all my vac lines. im kinda stumped on what could be causing this and have been holding off on driving it till i can figure what it is. maybe a bad coil (er but why the same rate of jerk/pop even at dif rpms) or even bad fuel pump or filter?

All your help and suggestions are greatly appreciated.

89 GTU Manual. all stock and 150k miles on it (saving up for rebuild :D )

The injectors might be starting to leak so it pops when there is a little excessive fuel. A new filter wouldn't hurt.

Ok cool ill look into the fuel system and see if i can find aything. Thnx for the help =)

You should test your TPS..
Using test lights or voltage at idle readings will get your idle setting perfect, but you could still have a worn out TPS resistor.
-The test:
Pull the TPS connector off.
Get an analog (needle type) VOM set to the 1K scale.
Connect it to the pins for the orange & green wires.
Open the throttle enough so you can test the TPS plunger through its full stroke.
Work the TPS plunger in & out, the meter needle must swing smoothly from ~0 to ~5K ohms.

As the TPS wears, it can give non-linear or inconsistent signals to the ECU.
A worn out TPS may give 1K ohms at idle, but have a drop out or short further up the scale.
A drop out at mid scale will tell the ECU to idle at that point & give a fuel cut hesitation.
I had one go open at the top which made the S5 ECU go nuts, giving random fuel cuts.