Idling high

[Chrispbrown36]

My 87 V10 seems to always idle high. I have set the idle as they say it should be (dead 0 with the wire unplugged) and it seems to idle high after the normal warm up. I have tried retarding timing and advancing timing and it still sounds high (no tach so I can't say for sure at what rpm). I am wondering if the aftermarket idle air control valve has something to do with it, but have not tried trading it out for an AC Delco IAC. Plugs, wires, cap and rotor are only about 6 months old. Anyone have any ideas?

[barry1982]

I had a similar problem with my 93 GMC. There is a gasket between your throttle body/intake that sometimes develops vacuum/air a leak. Your computer compensates for the extra air by giving it extra fuel, and the result is a high idle. No guarantees this is the problem, but it is common and wouldn't hurt to check. (this new gasket is cheap, and not overly hard to change)

[Chrispbrown36]

I rebuilt the throttle body back in the fall so I really don't think it is that, but I am going start looking for a vacuum leak again.

[87Skier]

Originally Posted by barry1982

I had a similar problem with my 93 GMC. There is a gasket between your throttle body/intake that sometimes develops vacuum/air a leak. Your computer compensates for the extra air by giving it extra fuel, and the result is a high idle. No guarantees this is the problem, but it is common and wouldn't hurt to check. (this new gasket is cheap, and not overly hard to change)

What other symptoms would this cause?

[ZacharyDouglas1992]

Have you checked the coolant temperature sensor by the thermostat housing at the front of the motor? I believe this is what the computer uses for cold start/idle. Your truck might be staying in that higher idle if that sensor is out. looks like this...

[CSHADES]

like Barry said the gasket between the throttle body and intake was famous for failing and causing higher than normal idle speeds. I would still look at it even if I had just replaced it a while back.