I have a 98 that won't idle to save your life. New sensors, new fuel pump, new throttle control, I can't remember what all has been done at this point. If you can get on the road the car runs like a beast. Get in town, stop at a light dead. You literally have to drive it with a foot on the gas and one on the brake. Suggestions please thank u

 

A clue of what engine is in it? We are going to waste a lot of time guessing stuff and you say We already did that.

I start off, EGR Valve leakage test?

I do not believe either V6 or V8 were drive by wire in 98 so what do you mean by throttle control? Last time I check your foot controlled the throttle. Did you mean the IAC motor, was the proper homeing procedure done to it after it was installed?

Was the fuel pressured tested?
How old are the plugs and wire?
If the plug where recent how do they look?
Are there any code stored in the PCM?
Do you have access to a infrared heat gun?

 

I don't have an infrared gun. It's a v6 motor. It was at the Chevy dealership over weekend getting things tuned n tested n they were suppose clear everything. I know they replaced somethings. Plugs n wires are new.on this car it has a throttle control valve and I replaced that. Egr has been tested I believe n should b good

 

I don't think I can help you, I am a former GM Master Tech and I know my way around the 3800, There is no such thing as a throttle control valve on a 1998 3800. Just goggle it, if it existed there would be 100 adds trying to sell you one and 20 youtube videos showing you how to replace it. Now search 1998 Camaro IAC, you will see what I mean. I would guess you are not a technical person. The only way this could work is if you have the ability and access to tools to preform tests. We tell you what to test and you report back with finding. Vague "I think the dealer did this or that" is not going to work. We will just go in circles. If the dealer is having trouble finding an issue its not going to be easy to track down. Honestly all you are going to get online is, that happened to my car and it was X, the problem is there is not just one thing that will cause an issue like this and if you just start swapping parts on a 20 year old car you can complicate the issue. Clips and connector tend to break on 20 year old cars.

Don't take it personally I have had friends that are car guys and I talked with them for hours trying to talk them through an issue on the phone. Then when I gave up and went to their house I found they where doing a test wrong and giving me bad info. In many cases I figured out the issue in less then 10 minutes.

Here is my list of the things that could be wrong.

Fuel pressure (most likely a regulator issue)
EGR valve leaking a small amount of exhaust into the intake.
Failing or dirty fuel injector(s)
Dirty IAC port
A lazy/failing IAC motor
IAC motor not homed
ICM internal issue
Secondary ignition system failure. (cracked plug or a bad crimp on a wire)
Vacuum leak into a single cylinder.
Sticking valve
Stretched timing chain.

I am sure I am forgetting something.