Recently my 94 f150 4.9 with a 5spd has been starting with a high rev at initial start. it comes down after a couple of seconds and then jumps to a high idle (same as initial start) and then returns to idle within seconds again .. any thoughts would be helpful. thanks

 

How high does it go? As additional air is metered in by the AIC, a cold start will have a higher idle speed. A vacuum leak would cause a fluctuating idle speed as you describe.So can many other systems.

 

i don't have a tach in it so i don't know how high it revs at start up, but it seems excessive to me. It only lasts for about 10 seconds and has no fluctuation in idle after that. Even when i shut off and restart the truck it is normal. it basically does it when it sits overnight. I am going to check for vacuum leaks and the tps. thank you for the suggestions

 

I would doubt the TPS has a problem. If there's a problem, you will have symptoms all or most of the time. It won't be bad for just ten seconds and all is well.You could make sure your IAC solenoid is functioning, its pintle and bore on the throttle body is not carboned up.

 

Test the TPS, ACT, ECT...

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