Mysterious idle problem

I have this problem where the engine idle speed raises and lowers on its own. It only occurrs when the engine is hot, the transmission is in drive and my foot is on the brake. Also, the problem goes away when the outside temperature is below 32F. I changed the idle air control valve and it did not help. If the normal idle speed is 600, it suddenly raises to about 900 then overcompensates and goes to 300 before stabilizing out at 600 again. What is the problem?

hey, i had the same problem the chevy dealer said it was a computer problem on my 1999 c/k 2500
and needed to be reprogrammed per gm

hey, i had the same problem the chevy dealer said it was a computer problem on my 1999 c/k 2500
and needed to be reprogrammed per gm


Tommy-

Check your fuel pressure regulator. This is a common problem on '99-up C/Ks.

The fuel pressure regulator is located on the driver's side of the intake manifold, it's a little cannister about the size of a large walnut, held onto the manifold with a clip and it has an vacuum line coming out of it.

Start your truck for a few minutes, shut it off, wait five minutes, remove the regulator and vacuum line, turn it over to see if you have fuel coming out of the vacuum port. If you have fuel present, then you need to replace the regulator.

This should clear up your idle problems. Shop cost for the part is around $69.00. Also shop the price, you'll find GM cheaper than the parts stores.

-slacker