Rough Idle

[Achilles]

I've had a rough idle issue with my '86 since I bought it a few months ago. It almost has a lope on cold start, but once it warms up it idles fine. There's no check engine light on to indicate a malfunction. Someone told me it could be the EGR or the switch and sometimes the switch goes bad. I'm not familiar with the switch or where it is even located. I though I would check with you fine folks first before I randomly start replacing parts.

Also, once this problem is resolved, I've been considering porting my stock plennum and runners. Has anyone tried this and how difficult of a job is this? And what were the results of this mod?

Thanks for any help....

John

 

[vetteboy86]

If it only happens on cold start, and since you have no engine light I would look at the Throttle body. Most times if the EGR switch is bad it will put the light on. I know for a fact my bro's car did. Check the TB for a gunk build up, at or around the butterflys. I dont know much about the funcion of the idle air control (IAC) but I am sure it could have some cause as well. Hopefully you will get an answer soon. About your porting question, I am going to buy a spare plenum and port that. This way if the results if any, aren't what I like I can change back.


Craig

 

[tkrphxr]

Egr

The egr temp switch is located in the egr pipe where it goes into the intake manifold at the back right side of the engine. The switch has a single wire going into it and sets straight up and down in relation to the engine. I was thinking that a bad egr temp switch would throw a code but can't remember for sure. Good luck!!! Charlie.

 

[Vettefan87]

If it only happens on cold start, and since you have no engine light I would look at the Throttle body. Most times if the EGR switch is bad it will put the light on. I know for a fact my bro's car did. Check the TB for a gunk build up, at or around the butterflys. I dont know much about the funcion of the idle air control (IAC) but I am sure it could have some cause as well. Hopefully you will get an answer soon. About your porting question, I am going to buy a spare plenum and port that. This way if the results if any, aren't what I like I can change back.

Mine does still idle a little rough, it is almost like it has a little mild of a cam in it, once I let it run for a couple mins it goes away. If you are not getting a code, I would not get to worried about it, and as long as it comes out of it when it gets to operating temperature. You are fine.

The egr temp switch is located in the egr pipe where it goes into the intake manifold at the back right side of the engine. The switch has a single wire going into it and sets straight up and down in relation to the engine. I was thinking that a bad egr temp switch would throw a code but can't remember for sure. Good luck!!! Charlie.

Yes it will throw a code.

Now to porting the plenum, If you use the search function You will find a ton of information on how to take the plenum off and what not. I did not have to take mine off, since I had to rebuild my motor. What I did was use a dremel and a drill with a grinding type bit to grind away the ridge right at the front of the plenum. The only bad part is, is that you will not notice anything on the "butt" dyno. Good luck

Justin

 

[jmccloud]

Rough Idle on start-up

Check the recent thread by Mad-Mac

 

[Achilles]

I appreciate everyone's help and I did check out the thread by Mad Mic. I also drove the car again today and upon paying closer attention, it still has a lope even after warm up. But not as bad as when cold. It really does seem like it has a mild cam in it. And it runs like a bat out of hell. Maybe I'll leave it alone. This weekend I'm replacing plugs, cap & Rotor, wires, etc. I may attempt to check out if there is grime in the TB and get that cleaned up.