idle problems

[shoredune]

Hey everyone,I'm new here and after reading how everyone is so helpful I joined up.
I have an 85 vette,when first started it idles up and down when it's at operating temp
it runs fine. Changed wires cap,rotor etc. always take good care of this thing and I'm thinking maybe an electronic problem. Does anyone have any suggestions?
Thanks.
Also cleaned throttle body.
also changed coolant sensor

 

[Dougs91]

When you cleaned the throttlebody did you check the condition of the iac valve? It can get dirty and cause the idle hunting. Also, the butterflies in the throttlebody can get loose...Good Luck, Doug

 

[rrubel]

Also sounds like a possible vacuum leak that gets sealed when parts expand as they warm. TB gasket or intake gaskets?
[RICHR]

 

[cntrhub]

Also sounds like a possible vacuum leak that gets sealed when parts expand as they warm. TB gasket or intake gaskets?
[RICHR]

That is the first place I would look. You said it starts fine but when those parts move from the paper and that paper is now a leak to the air as parts expand, I have to rrubel the TB paper change is pretty much a single edge razor and basically 4 long bolts and have at it.

 

[shoredune]

Thanks everyone,I ordered the TB gasket today.......keepin' my fingers crossed.

 

[ibuyvettes]

The vacuum leak (if you have one) could come from numerous places. Check all vacuum lines, and spray F.I. or carb cleaner at the base all around the intake manifold (when cold) If the idle corrects while doing this or you actually see the cleaner get sucked in thats your problem.

The IAC would set off the check engine light.

Also check your fuel pressure and Fuel injectors.

And lastly, Have fun.

 

[onedef92]

Be sure and remove both the throttle body (TB) and Idle Air Control (IAC) motor pintle.

I like to clean both using a can of that Valvoline Synthetic TB Cleaner, an old toothbrush and a large plastic bowl to put the TB in while I'm cleaning it.

Don't forget to replace the IAC motor gasket. If your TB gasket kit doesn't contain one, you can cut one out of a sheet of gasket paper like I did. Put a dab of motor oil on the IAC gasket to ensure a tight, leak-free seal.

I like to clean my TB and IAC pintle annually. It really mellows the base idle and improves throttle response, too.

 

[gmjunkie]

I'd also check your temp sending unit!!Just because the gage works doesn't mean the sensor to the ECM is good!! It may be not telling the ECM that the engine is Cold,and be haunting all over the place for the right setting!!

 

[cntrhub]

The coolant temp will read say a 60 C or 80 centigrade... Depending on the code page or fuel injection in general, I the engine should run fine being it is now in backup mode, (if the coolant temp sensor was out of the loop... Yes or no the car will not 'hunt'?