I just bought a 1990 F-150 with a 5.0. The rpms rev up to 3000 and stay there on 1990 Ford F-150

It really stresses the transmission and brakes but the rpm's go to about 1500 when I put it in gear and race back up when I put it back in park.

by in Darlington, SC on November 23, 2012
3 answers 6 comments
ANSWER by on November 23, 2012
Vacuum leak, idle air control troubles. That is a good place to start.
ANSWER by on November 23, 2012
I would cheak your throttle position sensor unplug it and see how the rpm is if it drops down than that might be your problem.
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ANSWER by on November 23, 2012
Another example of taking to the mechanic BEFORE you buy, not AFTER...anyway, you need to take it to a mechanic this time so he/she can tell you what is wrong...
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COMMENT by on November 24, 2012
Thanks for some worthless advice about taking it to a mechanic. I bought the truck to tinker with and try to learn about minor repairs with.
COMMENT by on November 24, 2012
That is the best way to learn is get your hands dirty. Go for it and let us know what you find.
COMMENT by on November 24, 2012
I removed and cleaned the AIC and also replaced the temperature control sensor but neither worked to bring the rpm's down. The idle is so high that it makes it hard to listen for a vacuum leak. Any suggestions?
COMMENT by on November 24, 2012
Check pcv hose under intake plenum on right side to see if it is intact. Also booster hose as if it is a vac. leak it is a big one. I guess throttle stop screw is not cranked down? If no vac. leaks found i say it is iac problem.
COMMENT by on November 24, 2012
Well...lamecock man will have a lot of time and moments tinkering with his new truck...while he is at it, he should check a cocked throttle cable, or a cocked idle screw...maybe he might find something hard we missed. good luck.
COMMENT by on November 25, 2012
It's idiots like "your.mechanic" that give this industry a bad name and that I am trying to avoid! Quit sucking on those tail pipes and come up for air. I replaced the pcv valve, the egr valve, and the aic valve and still have a problem. It looks like the previous owner tried to give it a tune up because the plug wires are run in a disorganized manner so could it be a timing issue or does it still sound like a vacuum problem. When I crank it the rpm's are about 2800 and they drop to about 1300 when I put it in gear.