Engine Idle Low When Cold, High When Warm

[mhjo]

When I start the car in the morning the idle is very low. After driving moderatly for a while it gets to normal operating rpm. If I drive the car hard and it's a hot day the idle rises way up (1500 rpm)

This has haunted me for years, and noone has given me an answer to what the problem is.

The carburator is an Edelbrock 500cfm with electrical choke.

 

[Jake2012]

It's possible your carby might have an air leak and is sucking air. Check the main gaskets first and if not, then check the carry itself .

 

[mhjo]

Yes, we will check this. Thanks.

 

[j69302]

Not sure if this can happen on edelbrock carbs, but the fact that you say it idles high after you drive it hard, makes me think the choke is re-engaging the high idle. I would check the adjustment of the choke. It is possible the spring is installed wrong or adjusted far enough out that it re-engages.

Next time it does this, take the air cleaner off and see if the choke flap is closed.

Taken from Edelbrocks website:

Q: I can’t get my idle below 1,000 RPM with your Edelbrock carburetor, what should I do?
A: Check for correct choke operation and adjustment. Make sure that the fast idle cam is not causing this. Verify the throttle arm rests on the idle speed screw. It is important to verify throttle linkage, and or throttle blades are not binding and have a free range of operation. Throttle return spring should be correctly located and adjusted. In most cases, the return spring should be positioned on the top of the throttle arm forward. This should have been confirmed when the Wide Open Throttle test was performed during the initial installation of the carburetor. Make sure all of the vacuum ports on the carburetor are being utilized or blocked off.

 

[mhjo]

Thanks, we will check this