Engine tends to overreact to quick changes

[ghatid]

I have a weird issue that I can't really explain well, but I will give it a shot. I've kept it off the forums because I didn't have enough information, but I think I might have enough for someone to help me out.

Since I've had the car, I've always felt that the engine brakes a little rougher than it should even at reasonable low RPMs (2-2.5k), but everything else is great. Idle is fine, power seems fine, compression, etc.

My complains:
1. Car takes a few extra turns to start.
2. If I tap the gas instead of pressing it, the car overshoots and then undershoots and seems to be starving for air or gas before it corrects itself.
3. If I abruptly release the gas in 1st or 2nd gear, the whole car shakes and struggles for a moment before catching up again. I know our e30s have pretty heavy engines and the engine brake is pretty strong, but this happens even at 2k rpm.

Recently, I found out that I can solve all 3 of these issues by unplugging the AFM and then plugging it back in. If I do that, the car starts up quicker, it switches between gears quicker, and it's much smoother if I abruptly release the gas in 1st or 2nd gear. The weird part is, after driving it around for maybe 1-2 minutes, it goes right back to having the same issues.

I grabbed a different AFM from a pick+pull and it does the exact same thing.

Is it possible that somethings wrong with my computer? Is it somehow telling the AFM the wrong thing and by unplugging the AFM and plugging it back in, it resets everything and is fine for a bit, but then messes up again?

Thanks for your help.

[TobyB]

I would first rule out an air leak into the intake from somewhere...

t

[dnguyen1963]

Vacuum leaks would be the suspect.

[Ether-D]

Maybe check the connector for your afm on the harness. I wonder if it's corroded or something. It's odd that unplugging it would affect things the way you describe unless it's loose somehow or corroded. Only related thing I can think of is the connector. Vacuum leaks are very common also as stated above.

[ghatid]

Vacuum leaks would be the suspect.

Okay, I've gone through the list of things that can leak before. It was what I was suspecting since that seems like the most common issue, but I didn't find any leaks the first time. I'll go through it again and see if I missed something.

Thanks!

[packratbimmer]

Throttle body flap adjustment correctly? Throttle position switch adjusted?

[nrubenstein]

It's probably vacuum leaks, but clean your CPS as well.

[ghatid]

Checked the throttle body flap adjustment and position switch and cleaned my CPS before. I guess it can't hurt to do it again. It's just weird that it goes away after I reset something and then comes back after I drive for a little bit.

Thanks for the suggestions!

[TobyB]

That makes it sound like something that's a bit outside tolerance that's confusing the computer-
once the ECU 'learns' the engine, it gets it wrong, and moves its corrections the wrong way.
AFM, especially, can do this. Incorrect fuel pressure. Other sensors that are not accurate, like temp...

Vague, I know...

t

[ghatid]

That makes it sound like something that's a bit outside tolerance that's confusing the computer-
once the ECU 'learns' the engine, it gets it wrong, and moves its corrections the wrong way.
AFM, especially, can do this. Incorrect fuel pressure. Other sensors that are not accurate, like temp...

Vague, I know...

t

Vague, but I think the problem isn't an obvious one. Thanks for the ideas. I'll check other sensors while I'm in there. 2 AFMs did the same thing. I was thinking that maybe the PO put a different "performance" chip or something that is messing it up, but it all looked stock when I pulled it apart.