Mechanics

FAST IDLE

1987 Ford F-150 • 6 cylinder 2WD Manual • 164,000 miles

On July 26 I asked "1987 Ford f-150, straight six. Starts but I have to keep reving the engine until it warms up. Once it warms up it will idle at 550 to 700 rpm for a few seconds, and then slowly (3 to 4 seconds) idle up to 2500 to 3000. When I turn it off and restart, it idles at 1500, quickly goes to 550 to 700, then slowly climbs to 2500 to 3000. Over and over. When I disconnect the iac it wont idle at all, but will run if I pedal the gas. Actually changed the iac, but no different. Not sure what to check next. Old dirty engine."

hmac300 replied "clean the throttle plate with choke cleaner and check for vacuum leaks with the choke cleaner around intake ports andthrotle plate connections. Then taek out your egr vvalve and see ifit's all gunked up around the pintle valve inside. It may bestuck open ornotworking right."

pretty sucky answer. I guess thats all I get for $20. Anyway, I did a little more tinkering. Changed a bunch of vacuum hoses. No different. Changed pvc valve. No difference. Unplugged green hose from egr. No difference. Upplugged the electronics from the egr. No difference. Pinched off difference hoses (brake booster, cruise control, heater control) to see if engine would change noises. Nothing. The idle pattern is extremely repeatable. Once warmed up, on restart without pressing gas pedal, engine starts at 1500, settles at 550 to 650 for 2 or 3 seconds, then climbs to about 2500 in about 4 seconds and stays there. Over and over and over. Something is getting a rotten signal from somewhere. I even unplugged the battery to see if it would reset. Could it be the pcm? If I take the pcm out can it be checked?



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Dickie
July 28, 2011.



Any luck yet. Have you watched throttle linkage at body when this happens to see if it moves at all?
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Tiny
Fixitmr
Oct 19, 2011.
And what about monitoring voltage to IAC?

Tiny
Fixitmr
Oct 19, 2011.

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