5.0 Engine problems

[mjbtv]

My 87 5.0 runs weird. At start up the idle will lope, then run at 800 rpm then shoot up to 1500 rpm and stay there. If i drive it the car will stall when i let off the gas pedal. Any thoughts on this one? There are no codes present and the fuel filter has been replaced along with a new cold air intake tube and filter.

[squeeeg]

What mods have you done to the car? This sounds like the surge demon that is present in many foxes.

[mjbtv]

This is a stock 302. OBDI scan shows no codes so it has to be a mechanical problem.

[squeeeg]

Have you done any tinkering or anything lately. It kind of sounds like a TPS but that should throw a code at you. What did you use to test the codes.

[SNW BLUE BY YOU]

It sounds like an idle air control [IAC] valve issue. This may or may not set a DTC.
This is the valve on the front of the intake manifold. It allows for proper idle when the throttle is closed,by allowing air to bypass the throttle plate.
It is common,especially on high milage cars for them to get carboned up and stick closed.
This can sometimes be verified by causing a vacuum leak[for testing only] If the vehicle idles, that is your problem, or have the IAC monitored for proper op, duty cycle should be around 35% with a good idle.
I may also be reading this incorrectly. Make sure you have no vacuum leaks due to that cold air you installed and all connectors/hoses are properly installed and secured.
Hope this helps.