This is for a '91 L98 TPI. Not quite sure where to go with this. It has been overheated once...did a full compression check and all cylinders checked fine...

Idle remains constant in the 3000, 3500 range. Any ideas?


Also, I don't see any evidence of coolant leaking over...so, it couldn't be a head and/or gasket, right? Or could it? Anything else that might be causeing this issue.

 

Wow that is high!

With an above usual idle I usually look for vaccum hoses that have either cracked or broken off and give my throttle body a clean..

Look at the routing diagram under to hood, you should see where all the vac hoses goto. Most goto the plenum on the TPI.

Check the PCV hoses (the ones going to the valve covers), the brake servo hose (back left of the tpi to the black brake booster), theres also a hose on the right side and left side of the throttle body (small ones to egr valve and cruise control).

Take the black dual snorkel off the front of the throttle body, and make sure that the butterfly valve is closing all the way by moving the throttle with your hand. In the throttlebody sometimes gunk will let air bleed past. It might be a combination of cracks or disconnected hoses.

I live i AZ, vaccum hoses dont stand a chance in this dry heat, I am constantly finding ones to replace.

Has it always done this, did anything change? If so what?