Engine racing after start up

[GaryJ]

I recently purchased an 88 Cheyenne K series (1500) pick-up. It has 255,000 miles on it (110,000 with a reman engine). The truck runs fine after warmup but races when cold. It just seems like it won't kick down. After a few minutes of driving it kicks down to a normal idle and is fine. Any suggestions on where I might look. Thanks

[GaryJ]

I should have mentioned it has a 4.3 litre V-6.

[ChevyTech]

Hi GaryJ, I see you are new to the board, welcome.

The ECM and IAC (Idle Air Control) allow air to bypass the throttle plates to give a faster idle when the engine is cold and control the idle speed when warm. Being it does slow down warm, the IAC should be ok.

If you had access to a scan tool you could look at the idle air count when the engine was warm and you would know if you have a problm or not.

Being you most likely don't have a scan tool, check for any vacuum leak. If you have a cold idle, that is faster than it should be, look for items like a leaking TBI base gasket, leaking vacuum hose, leaking brake booster, stuck open pcv... If the engine can draw extra air in from any source it will effect the cold idle speed.

Sometimes the fan clutch will make the engine sound like it's running faster than it is. If the truck is real hot when you park it it will take a few minutes of running before the fan clutch lets go when you start it.

Unless you have a worn out TBI unit kicking the throotle will not change your fast idle speed. There is no fast idle cam like a carburater has.

Hope this helps
ChevyTech

[GaryJ]

Thanks for providing me with this info. Hopefully I will find time this weekend to start eliminating things. I am a backyard hack who doesn't mind getting his hands dirty but I am a tad bit short on knowledge. The power of the internet is there because of people like you. Thanks for being here. :p