E150 5.8 Stuck on Fast Idle HELP!!

my 1994 E150 conversion van, decides to go to fast idle, then stays there. Like a stuck throttle cable, but the cable isn't stuck!! I don't know what to check! there are no error codes, the Ford dealer JUST installed and adjusted a TPS, so what's next??

Any ideas are apprecated!

On the side of the throttle body is an ISC which is Idle Speed Control. It will be mounted with 2 8 mm bolts. Remove this and clean this with a mild cleaner. A carb cleaner is too strong and will ruin it. I use Snapon Motor vac solution or Seafoam. Pour some in the 2 holes and put two fingers over the holes and shake and dump it out. Do this till the cleaner is no longer black. See what that does. It would not hurt to clean the throttle body the same way. or use a brush with soft bristles.

I have exactly the same problem with a 1992 E 150 with 5.8 L engine. I have replaced the idle air valve -- but no change. Did cleaning your throttle positioner as one person suggested, fix the problem?? Please let me know what you found.

Thanks
bob.james@pgn.com

Is the throttle plate closing? Do you have a check engine light? Do you have a volt meter? Check for any large vcacuum leaks. Try unhooking the ISC and see if Idle comes down.

Is the throttle plate closing? Do you have a check engine light? Do you have a volt meter? Check for any large vcacuum leaks. Try unhooking the ISC and see if Idle comes down.

I have checked for leaks with carb cleaner -- but none were aparent. I do have a volt meter. I replaced the idle air control valve with one from NAPA and it now seems to run even faster than it did before. I will have another look at the throttle plates -- although I hosed them down with Carb cleaner when I installed the new Idle air valve. There is no check engine light showing and no codes. I believe the idle air valve is open without any voltage -- so I don't think it should slow the idle speed by removing the connector -- but I will try that.

Thanks,

Bob

Never use carb cleaner it leaks down the shaft and fries the TP sensor. I was going to have you use the voltmeter to check for tp reading at idle. ISC unplugged should give you base idle of around 6 or 7 hundred rpms. All the ISC is is a fluctuating vacuumn leak. To rule it out loosen screws and slide cardboard under sensor to block holes and it should idle very low. If that works and unplugging it doesnt it is either on backward or it is bad. Is there a plate under it? Some had this and it can only go on one way.

It's possible to have an intermittent code. Try checking for codes while the engine is cold, then again at operating temperature.

Other possibilities is the computer is telling the engine to run at fast idle because of faults with temperature readings simulating cold weather. This would be the Air Charge Temperature sensor (ACT), located near the air filter or the Engine Coolant Temp sensor (ECT). You should have two of these located near the thermostat. The 2 wire one is for the gauge and the 3 wire one is for the computer. Sunpro sensor tester is a valuable tool in these situations. Easier to use than a volt meter.

ECTs and ACTs rarely fail on Fords but it could happen. More likely fried tps from old age or carb cleaner. Also make sure you have a FORD plastic PCV they dont like aftermarket ones.

Fixed!! The plates were not closing.. Seems the shaft that goes top to bottom was corroded, and preventing it from springing back to closed position! So, after dismantling the unit, and finally figuring out how to get the shaft out, polished it and put it back ( the dealer wanted MUCHO bucks for a new body) it returns to idle correctly.

Now I think I've trashed the position sensor. Oh well, here we go again!!

THANK you all for the posts!!!!!!

I'm having the same problem except that I put a new Idle Speed Control and changed some old vacuum lines and no results. It looks like the plates are closing. There's a valve on the opposite side of the ISC. The vacuum line to this valve was gone, which is why I changed all of the other vacuum lines to make sure I didn't have this problem with other lines. Could this valve be causing the problem? Update; I pulled the plug on the ISC valve and it did indeed drop to 6-7K r.p.m. What now and how long can I run it like this with what kind of results? Hey, gotta roll you know . . .

i HAD A FAST IDLE ON MY 1994 E-150 5.8l.
Turned out to be the Throttle positions sensor. Replaced it and idle is down and the hard shifting went away, but now it seems to have an intermittent miss and rough idle. 3 mechanics cannot figure it out!