1988 350 tbi Rough Idle When Warm

[Tristen]

I recently acquired a 1988 Chevy 2500 with the 350 tbi in it that has about 80k miles and had been sitting for a very long time. When I got the truck it had a miss fire, back fire, and very poor throttle response. Since getting it I replaced the fuel pump, leaking fuel lines, Idle air control valve, MAP sensor, EGR valve, both injectors are new(not reman), and new spark plugs. After replacing these the throttle response is working correctly and there’s no longer backfires at idle or on the gas. But when driving the truck to work and parking getting ready to turn the truck off it’ll start misfiring and essentially sounds like it has a cam in it, sometimes even completely shutting off. But 8/10 times if I shut it off and turn it back on it’ll stop doing it. it also idles high when warm and stopping at stop signs or stop lights it seems, but this could be I’m not used to driving a vehicle with this big of an engine considering I’ve been driving a ford escort for the previous two years but I had a 97 with spider injection and don’t recall it trying to pull away like this. I figured I got a faulty idle air control valve so I warrantied out the part and installed a new one and the morning after I went to start it wanted to idle rough, so I shut it off to restart it seeing if it would stop like it normally would and it just sat there and cranked. It only started when I gave it some throttle. I’m thinking on getting maybe a different brand idle air control valve to see if this would help but figured I’d ask to see if anyone has insight on what else would cause this

 

[Das Hatt]

How old are the plug wires, cap, and rotor? When you installed the IAC valve, did you perform the relearn procedure that's in the factory manual? Have you checked for any vacuum leaks?

Before replacing the fuel pump, MAP sensor, and EGR valve, did you verify they were not working? The stuff you can get today at the parts store is hit or miss as far as quality.

 

[Tristen]

plug wires and cap are newer, I don’t know about the rotor I didn’t take it apart. I didn’t know there was a relearn procedure for the iac and I don’t have the manual that came with the truck. Fuel pump was replaced because it was leaking out of the metal lines, with the research I did when trying to figure everything out the first time I figured it would be worth it to replace the edge valve and the map sensor at the same time because they looked original and I didn’t want to have issues further down the road

 

[PlayingWithTBI]

I didn’t know there was a relearn procedure for the iac and I don’t have the manual that came with the truck.

Here's a procedure that talks about the IAC and the TPS. It's old but is still informative.

 

[Tristen]

Copy, thank you.