Fast Idle- 96 F150

96 F150, 5L, auto not a daily driver but the other day I took it out and noticed the idle is over 2k. To the point when I put it in drive, I am afraid it with break a u-joint. Letting it warmup, no change. Going down the road shift to neutral and it goes to 2500 rpms.

Any thoughts or ideas on what to check would certainly be appreciated.
Thanks,
Gumby_CT

Check for a vacum leak first. The pcv valve on the 302 is on the rear of the right valve cover, under the intake plenum, and hard to see. The line to it is bad about cracking and leaking. Also the pcv valve can be pulled out of the grommet, if the line is disturbed because of other work or maintenence. Check all the lines and hoses, especially the molded rubber pieces, for cracks.

Try retarding your timeing.

I feel like I conquered the world :grinyes:
Problem solved. I hope it does not return.
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The short story -
I think fixing the vacuum leak followed by resetting the PCM fixed the problem.
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The details -
Note 1:
While looking for any vacuum leaks, I noticed a label which says clearly - "Engine idle speed, idle mixture, and ignition timing are NOT adjustable."

The truck has just been sitting so, I did not think an adjustment had just changed. I did find a vacuum line with a cracked rubber hose (90 elbow) just above the alternator going from the front of the throttle body back to the Vapor Management Valve (VMV).

Just the elbow, the 3in rubber hose, is not available w/o buying the plastic tube part which was not cracked. The next higher assembly was $50 from the dealer. I found something at the parts store for a lawnmower ($4) I was able to cut & make work.

But just replacing the cracked hose did not bring the idle down.

I sprayed water over every vacuum hose looking for more leaks. Searched the forums. Read almost every post concerning fast/high idle, idle air control (IAC), and throttle position sensor (TPS). Had no idea where these things were before, now I know. Is this baptism by fire? Even resorted to trying that USELESS CD I bought from Ebay. You can only search the page you are ON. Time consuming & USELESS. Need to find a paper repair manual.

Ended up making a platform to stand on (my poor back) to finish working on this thing. The dealer told me I would have to drive it to re-train the computer, maybe as much as 100mi. With a 2k+ idle I was afraid I would break a u-joint everytime I put it in gear.

I measured volts/ohms, sprayed water, squeezed & plugged vacuum lines, test drove some, & read some more. Even found the PCV valve. Following the hose back from the intake is probably the easiest way to locate it.

I remembered reading some problems do NOT turn the check engine light on. Some say to disconnect the battery to clear the computer (PCM). I avoided doing that because I didn't want to program the radio all over again. Plus I can never remember how to set the clock :confused:.

I thought the PCM has to have its own fuse. I found it in the owners manual. Tried a few more things then out of total frustration located the 30A PCM fuse in the engine compartment, pulled it for about 20 seconds, started it, like a "new truck". BINGO, had the big O.

The only thing I could figure is the vacuum leak did NOT turn on the Check Engine light but sent a code to the PCM causing it to idle FAST. Replacing the hose fixed the leak but the fault code remained in the PCM. Does that sound feasible?

In any case, my only regret right now is that I never pulled the codes, in case the problem reappears. Which, from reading the forums, sounds like the next step in the baptism by fire.

I feel like I conquered the world :grinyes:

Now if I could only find a temperature gauge at a reasonable price!!!

Glad you got it fixed. Checking for vacum leaks is always a good place to start, with those symptoms:


""The only thing I could figure is the vacuum leak did NOT turn on the Check Engine light but sent a code to the PCM causing it to idle FAST. Replacing the hose fixed the leak but the fault code remained in the PCM. Does that sound feasible?""

The vacum leak itself wont set a trouble code, but usually causes a code to be set for something else.(O2 sensor, iac valve, rich mixture, lean mixture...ect) This is because the computer will try to compensate for the vacum leak, and does everything it can think of to keep the engine running:( alter the timing, change the fuel delivery, change the iac valve trying to make it idle...ect) A large vacum leak is the equivelent of cracking the throttle open and not getting any extra fuel to go with the extra air. Sorta like a carbed engine on a cold morning with the choke not working. A carbed engine with a big vacum leak will usually just go dead because its too lean, the computer trys to keep these injected engines going. The computer will usually reset once the vacum leak is fixed, after a few restarts, but if it doesnt, you did the right thing pulling the fuse. I always hook a spare battery to the cables when i have to remove a battery for the same reason you pulled the fuse. I dont have manuals on all those radios and clocks, and some of em are a booger to get reset. People get mad when they have to reset all that stuff, especially their radio station presets. LOL