Continuous Very Rough Idle

[Marccus]

I have a very rough idle. I open the throttle body up at idle with that little screw throttle body stop and the roughness goes away. But the idle is about 1200 rpm.

Now I thought that the IAB valve would negate my opening up the idle when the computer adjusts the IAB valve to get back to normal RPM.

So that I don't understand.

I did a search and one of the most popular reasons for the rough idle is coil failure. I replaced the coil about 6 months ago.

I cleaned the throttle body, MAF, and the IAB valve.

Same problem.



All new wires, plugs about 1 year ago. So I don't believe there would be any oil in the plug wells especially with new plug well gaskets.

(Also FWIW, I sealed the rubber gasket, washer, and bolt with silicon gasket sealer as I assembled the items on the valve cover. This is the way to go as NO oil has shown up on the outside of the valve covers.)

Any ideas? Another new coil?

Go figure, original coil lasts 360,000 miles and this one may be gone in 10-12K.

'89 SHO.

 

[Bizzy]

Have you checked for any vacuum leaks? That's the direction I'd be leaning in.

 

[SHOtimer]

How are your o2's? I noticed before my CE light indicated mine where going bad, my idle quality was very poor.

That screw is not a proper way to adjust the idle....

What type of plugs are you using, I'd pull a plug to check on the quality of the plug - that can tell you a lot there.

Doug

 

[F-22 Raptor SHO]

Have you checked for any vacuum leaks? That's the direction I'd be leaning in.

I get it! Vacuum leaks...leaning

1: dont mess with that screw, you are making things worse.
2: Run the codes, see if it things the TPC or IAC is bad.
3: reset the idle first http://www.shoforum.com/showthread.php?t=75458
4: Suggest cleaning the IAC....that tubular thing next to the throttle body.