90 Chevy 5.7 Idles Issues

I have a 90 Chevy with a 350 TBI sometimes the iac will just start opening by it's self and idle up and other times it will idle down to around 550 rpms and die. I have replaced the IAC,ECM,TPS,Ignition Module and checked all grounds anyone ever had anything like this? It will only do this when put in to gear in park it idles fine.Thanks

I have a 90 GMC K1500 5.7 Auto that had a rough idle in drive. It never stalled but drove me nuts. I eventually figured out that the vacuum hose to the MAP was leaking along with the PCV gromet not sealing. After replacing both the gromet and the vacuum hose. The idle quality greatly improved.

What helped me was using a scanner and watching what was happening when the idle got rough. I could see that the engine was running rich and the ECM was trying to lean it out. My theory was that the PCV valve was not doing it job along with the MAP vacuum hose leak caused it to run rich.

Other things to look at are EGR valve, EGR solenoid and O2 sensor.

//2000CAYukon

I had a similar issue in my 91 Chevy truck. It was the wiring that went to the ignition module at the base of the rear side of the distributor. There was something loose in that area and it only had a bad connection when I put it in gear and the motor twisted. I found this out by leaving it running and reaching behind there and giving every bit of harness I could get to a firm tug in several directions. Be careful not to pull too hard but if this is the case with yours, you'll surely get it to act up. Then it's just a matter of tracking it down from there. Hope this helps.

I tried pulling on the harness replaced the distributor and sprayed around with carb cleaner to try to find leak but still no luck.

It's no longer idleing up just dies when in gear will idle down then just dies. Thanks