Revs to 2000-3000rpm on start up

Axle_tek · Feb 4, 2016

I updated my upper intake manifold to the 02 plastic style on my 96 and now it revs to 2000-3000rpm when started. Searched for vacuum leaks found nothing. Has anyone els tried the plastic upper manifold on a pre 97 ranger and had any issues? Wondering if the computer can't compensate and is causing the issue. I also did the heads, valves and cam position sensor. I tried unplugging different sensors to see if it would default with no luck. I hooked a scanner up and everything is reading normal. Any ideas? I'm stumped

ratdude747 · Feb 4, 2016

Sounds like a jammed IAC. Symptoms match and if you were doing intake work, it's a likely suspect.

Rearanger · Feb 5, 2016

Axle_tek said:
and now it revs to 2000-3000rpm when started.

How about RPMs after it warms up?

Axle_tek · Feb 5, 2016

ratdude747 said:
Sounds like a jammed IAC. Symptoms match and if you were doing intake work, it's a likely suspect.

I swapped in a known good IAC and nothing changed.

Axle_tek · Feb 5, 2016

Rearanger said:
How about RPMs after it warms up?

I honestly haven't gave it a chance to warm up. After all the head work I don't want to have it revving so high for long periods before I know everything is ok mechanicly.

stmitch · Feb 5, 2016

Is the throttle cable holding the throttle partially open?

Axle_tek · Feb 5, 2016

That was the first thing I checked... Ugh this is frustrating!

Rearanger · Feb 5, 2016

I'm not sure the IAC will rev it that high?? It does sound more like a throttle plate issue. It sounds like you're pulling in metered air which will raise the rpm.

TxGasRacer · Feb 5, 2016

Unplug your IAC while your engine is running and it should go down in RPM and it might even stall out because this is what adjusts your idle while the computer sends the command to open or close the IAC for idle control.If your engine stays with the high idle after you unplug your IAC then you have a vacuum leak somewhere and it is letting in unmetered air which causes a high idle condition.

Axle_tek · Feb 5, 2016

TxGasRacer said:
Unplug your IAC while your engine is running and it should go down in RPM and it might even stall out because this is what adjusts your idle while the computer sends the command to open or close the IAC for idle control.If your engine stays with the high idle after you unplug your IAC then you have a vacuum leak somewhere and it is letting in unmetered air which causes a high idle condition.

Please read the first post. I understand your trying to help but it is not a vacuum leak. Causing this issue. A vacuum leak that would cause it to rev that high would have to be 1/4" hole if not bigger.

Rearanger · Feb 5, 2016

Axle_tek said:
A vacuum leak that would cause it to rev that high would have to be 1/4" hole if not bigger.

Yes, I agree. Just adding air or just adding fuel would cause rough run and not that much rpm. Adding metered air and fuel would cause this.

Axle_tek · Feb 6, 2016

Figured it out. The IAC I got with the intake is apparently not the correct one for the truck application is basically backwards of the IAC that goes on the truck intake. It looks identical so until I compared the two I figured out 1. I had a bad IAC to begin with. 2. I was installing a good IAC backwards because I though that's the direction it was supposed to be. In my defense I didn't have anything to go off of. Thanks for trying to help tho guys!

Revs to 2000-3000rpm on start up

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