Stall sometimes after hard stop (due to low idle)

[tomballpkr]

I am planning to purchase a 2002 Explorer EB V8 from a friend. It has 95K miles on it but is immaculate and runs great.

However, on the way to pick up the check for him at the credit union, it stalled when I pulled up to a stop sign and made a hard stop. I have since been able to make it stall 10+ times by getting the RPMs up and then doing a hard stop, but it only stalls occassionally. My friend told me that the car stalled for his wife once about a month ago but they were never able to duplicate the problem.

Once warmed up, it idles at about 600 RPM. During most stops (soft or hard), the RPMs drop directly down to 600 and level out. Sometimes, however, the RPMs dip down below 600 towards 500 and then back up. On the occassions where it stalls, it dips down below 500 to around 450 and then stalls out.

My inclination is to think the IAC is the culprit. However, the IAC on this machine was replaced 1 year ago because of the infamous 'idle at 0 RPM' issue that plagues Explorers. It seems unlikely that it would have failed again and I am not even sure if this could be a symptom of that.

Any suggestions as to what the cause could be?

Yes, I took it to my mechanic to have it fixed but they 'could not duplicate' the problem. I am going over there tomorrow to show them but now I am not sure what they will magically do to fix it once I replicate it for them. I figured I should post a message on here and get some feedback. My friend would be handling all of this but he lives 45 minutes away and I have the car in my possession right now.

 

[ExplorerDMB]

That sure is odd. Hopefully a IAC is your only problem. Hope it all works out.

-Drew

 

[tomballpkr]

My mechanic said the problem would be difficult to resolve unless it got worse. I took it to the Ford dealer, they said a code showed up saying the IAC needed to be swapped and so they did that and said the car was fixed. Well, I picked the car up and there was no difference. They took another look at it and couldn't figure it out. I mentioned my friend had the torque converter swapped recently and then they started throwing out transmission-related items it could be.

I ultimately reproduced the problem for my friend and gave the car back to him. He is going to see what he can figure out.

Just wanted to close this out as NOT being the IAC.

 

[falls chic]

Check the EGR or the vaccum source to it.. Good luck.

 

[pj8847]

By any chance have you/anyone at the dealer reset the computer? After any sensor swap it is a good practice to reset the computer as it has to learn the behavior of the new sensor ( as it gets "used to" the old sensor and compensates voltages/signals as the sensor ages and it's electrical properties degrade)

The IAC, as I have found out recently is one of those things you need to reset the computer after changing. Mine was NEW and was faulty, it was drawing more power form the PCM to function than a "perfect" new part.

After replacing the IAC again, the truck idled exactly the same UNTIL i reset the computer.

What I did was start the truck with the old one, let it idle and warm up.
then I disconnected the plug from the IAC while it was running and of course the idle dropped to about 500 - 600 rpm...( from its unusually high idle )
I shut off the motor, and restarted it with the IAC still unplugged, the truck idled at 500 - 600 rmp, no more. ( if yours doesn't, you may need to "adjust" the idle on the throttlebody using the small adjustment screw underneath untill you are able to start the truck and have it idle WITHOUT the IAC connected at about 5 to 600 rpm, then proceed)

I then shut off the truck and disconnected the battery for approx. 15 mins ( I also turned on the headlight switch to drain whatever residual voltage that may have been left in the system)

While the battery was disconnected, I removed the bad IAC and installed the new one, and plugged it in. I then reconnected the battery, and started it up, and wouldn't you know it, no more drivability problems or idle problems.

Doing it this way in effect forces the PCM to "relearn" how to idle. works every time.

 

[n3hcp]

I came across this rather old thread while researching a problem I am having...in fact, the same problem described in the first post. Mine is an 03 XLT 4.6L 4X4 with 67K miles. I have cleaned the IAC and reset the computer. While cleaning the valve did smooth out the idle, the stalling problem still exists. Because of the very intermittent nature, I haven't had it to the dealer, I know I will get a "can not duplicate".
The stalling always happens immediately after the vehicle stops. Once stopped, if it is still idling, it will continue to do so...every time.
Just wondering if anyone else has seen and/or solved this problem.

 

[tomballpkr]

I am the original poster. The friend I was going to buy the car from 2.5 years ago never did sell it. He has been driving it as-is and just deals with the occasional stall. I guess the goal of my post is to point out that it did not get any worse over time.

 

[n3hcp]

I am the original poster. The friend I was going to buy the car from 2.5 years ago never did sell it. He has been driving it as-is and just deals with the occasional stall. I guess the goal of my post is to point out that it did not get any worse over time.

I was afraid you were going to say that!

 

[n3hcp]

New situation...my stalling problem has now become bad enough that I needed to take it to a Ford servicer. It's now doing the "stalls at red light" thing several times a day. I'll post if and when I get a fix.

 

[aznboi3644]

My 98 4.0 SOHC used to idle low like around 500-600 rpms....then I took off the throttle body and found out there was a pretty thick layer of carbon build up all over the inside...wire wheeled it clean and then it idled really high prolly around 1200-1400 rpms. had to lower the idle screw