I have a 91 Z28 305 TPI with manual transmission. The issue I am having is when the vehicle is in closed loop she has no power at acceleration, similar to having a bad vacuum leak. When the vehicle is in open loop (first drive of the day) she has a slightly higher idle (1000 -1200 RPMs) but she has plenty of pull and acceleration. Also, while in closed loop, idle is usually perfect and is steady. I have replaced all vacuum lines, searched for vacuum leaks, replaced plenum and TB gaskets, replaced O2 sensor, replaced EGR valve, replaced ICM, tested TPS, EGR solenoid, and MAP, and have inspected the entire wiring harness and repaired all problems I could find. I am starting to believe it is the knock sensor, which I plan to replace but I have to drill it out as it will not come out of the block and the sensor spins in its housing. Can someone please help me with this issue? One more tidbit - I bought one of those cheap splice-in-chips that splice to the IAT sensor leads that promise HP gains and better computer settings before I was wise enough to know better. Car ran great before hand and crappy after (actually she ran crappy until I found a vacuum hose cut and she ran great after I repaired it). I removed the chip and reset the ECM. Is it possible I damaged the ECM? This closed loop issue has been nagging me for about two years but it used to be a problem that was not constant and would rear its ugly head about once a month. Now this problem is constant. Again, I thank all of you that help in advance. There are so many tech savy and experience individuals here.

 

I know this thread is OLD but my 87 maf tpi car has the IDENTICAL problem, was wondering if there was ever a fix found on this...

 

It does sound like it could be knock sensor. Are there any codes? If it is the knock sensor it should throw a code.

I could also see the performance chip causing problems, usually those things are JUNK. lol (out of curiousity, did you see any difference?) how long ago did you remove it?

 

check for codes. Could be a bad ecm too. Check for codes first.

 

I imagine the opening poster is not going to reply since the thread is 3 years old. I had a code 44 the other day and my ecm is new, maf, ect are new, new engine.