I HAVE A 1997 F150 4.6 ENGINE. THE DARN THING WILL TURN OVER AND START BUT WILL NOT IDLE. IF YOU HOLD THE GAS DOWN IT WILL RUN BUT AS SOON AS YOU LET YOUR FOOT OFF THE GAS IT DIES. THIS HAS HAPPENED TO ME FOUR TIMES. IT ALWAYS SEEMS TO BE IN THE MORNING. THE ENGINE WILL EVENTUALLY START IDLEING AFTER ABOUT TEN TO FIFTEEN MINUTES. IS THIS SOME SORT OF VAPOR LOCK OR A BAD SENSOR? HEP PLEASE.

 

https://www.f150online.com/forums/sh...&highlight=IAC

and

https://www.f150online.com/forums/sh...&highlight=IAC

 

What Raoul said. Plus you can hit the IAC with a wrench, hammer, etc. and it will start immediately.

 

I had the same problem on a 99 explorer. Took it to a mechanic & he cleaned the idle air control valve & ever since its been fine.

 

I have a 1990 F150 XLT 6 4.9 EFI. Having the common rough idle at startup and stalling. Takes 3 or 4 starts to keep her running with some help from the gas pedal. Read all the posts and found some great info on this problem so I tried the following to isolate the problem. First I disconnected the plug attached to the IAC solenoid. Started the engine to see any difference. Things were far worse which told me the solenoid was possibly working. Next, I undid the 2 bolts holding on the actual IAC valve and removed the valve. I found the spindle arm that moves in and out coated with black soot. Being curious, I fired up the engine with the IAC completely off the throttlle body, the engine sounded like a jet engine. Did this for a sec. This definetly led me to believe that the IAC valve was not moving in/out properly. Without having a volt meter, I am betting the IAC solenoid is doing its job. Next step is to get some of the Valvoline Syntec Carb/throttle body cleaner and clean the valve. Also use a small wire brush to remove the deposits. Hopefully this will work. If not, I will have to get a volt meter to verify that the solenoid is getting the right signakl strength. If it is, then its time to check the fuel pump.

I am gonna take some digital pics of this experiment and post them. From surfing the net, it appears that the IAC is a common problem in all cars.

 

A dirty or worn IAC usually causes an erratic idle but it usually will run.

I would suspect a fuel problem--clogged filter or lines or a weak pump. Badly worn spark plugs can cause this too. Your eng. coolant temp sensor may cause the eng to be hard to start when cold. Check for vacuum leaks too.

Dan

 

To follow up. I Cleaned the IAC valve with Carb cleaner. I also checked the volts on the wiring going into the IAC solenoid as well as checking the resistance on the solenoid leads itself. All were within suggested ranges. Hooked it all backed up, disconnected the negative battery cable and reattached. I was told this would cause the computer to re-learn its idle sequence. Truck started fine, but now it is acting up again. Next I will try replacing the IAC valve. If this doesn't work then I will move onto checking the fuel pump, filter, and plugs. Worse part of this is that I have to go to a ford parts department to get the part. I hate dealing with dealerships.

 

When you guys take the IAC and EGR off, are you replacing the gaskets that hold them on? Of course my EGR has a gasket (most do) put there also seems to be a gasket under the IAC. I have called several parts places and none seem to have one. Now either it's a Ford only part, it's not available seperately, or it's always reused. Can someone please shed some light on this for me?

Second has anyone who did clean the EGR, IAC, or TB experiance problems. Most everyone here states they soaked the EGR and/or the IAC in Carb cleaner and sprayed or even brushed out the TB. While the manuals say not to soak them because the of damage to the EGR diaphragm and that the IAC is a electrical part and the TB has a special coating. I want to clean these parts but if it's going to damage them or shorten their life, it's not worth it.

 

no clean for me. It was a replace under warranty. The dealer replaced it. All I did was bang on it to get down the road because they were on backorder for a month or so. It was intermittent 'no idle'. Only seemed to happen when I was parked next to a Chevy and the owner was around.

I thought service might be giving me line about the backorder but, sure enough a guy in CA posted that he was on backorder before I mentioned it here.

 

No, I did not replace the rubber gasket when I installed the new IAC valve. The new $80 IAC valve seems to have solved my rough start problem. I disconnected the battery for a few hours to reset the computer. After running the engine a bit the computer relearned the idle sequence and the starts and idle are now smooth. For general maintenance I also replaced the fuel filter.