excessive high idle
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New User
Joined: Jul 2006
Posts: 7
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excessive high idle
can any one help me im actually stumped at the moment , i have a 1988 f150 302, runs excessive high idle hot or cold, i have replaced the idle control valve, temp sensor, can find no vacuum leaks, when temp sensor is plugged in it runs about 1800 to 2000 rpm , when unplugged runs 700, also engine intermittently cuts out and back in for no reason, could i have gotten a bad temp senor?, or could my computer sending wrong signals back out, or should i just replace all the sensors that are left.currently am driving with the temp sensor unplugged to avoid high idle and creating a hazzard by having to have to ride breaks alot and to keep from excessive speeds in town.
thanks rob
thanks rob
Freshman User
Joined: Jun 2006
Posts: 27
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its possible youve got a bad sensor out of the box its happened to me it could also be a bad ground in the wiring harness .But if unplugging the new sensor helps that much it might be the culpret . im fortunate enough to live by a u pull junk yard i grabbed a couple of iac valves and tried them out ther was a 150 rpm difference between the 2 i went with the lower one rpm wise . as far as the cutting out goes i think thats a ghost that everybody with speed density computers have tried to chase down if you look in the archives you will see that story over and over . i have an 1987 bronco that i have tried 3 computers in trying to get rid of the cutting out 1 out of an 87 1 out of an 88 and 1 out of an 89 they all work believe it or not and none of them threw codes other than a ok i went with the 1989 computer it gave me smoother shifts . If you dont live by a junk yard you can get a cheap $30.00 code reader and possibly be rid of youre trobles. sorry about all the jargin but you might also want to check youre fuel pressure regulator and see if theres gas in the line going to the intake manifold.
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Elder User
Joined: Jun 2006
Posts: 805
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Just a hunch, but did you disconnect the battery to install the sensor? You are talking about the engine coolant temperature sensor in the tree right behind the gooseneck, right? If it's the single wire unit, that's only for the gauge. If it was the 2 wire unit, that would be the ECT. Assuming we're talking EFI and not TBI for part location. Always a good idea to disconnect the battery for at least 10 minutes so the ECM can reset after a sensor replacement, and get re-educated. It will take several miles for it to figure everything out again, but mine did some pretty weird stuff when I replaced the plenum gaskets yesterday. It was pretty amazing to listen to it tuning itself to idle. Started out idling pretty fast, then slowed down real slow, and gradually climbed back up.
