I have a 99 E-350 V8 Triton 5.4 liter. I have put about 10,000 miles on the van in the last couple of months and its been running great. Today, whenever I take my foot off of the gas it stalls on me. I can't think of what could be wrong with it. Any ideas as to how to fix this would be appreciated.

 

the most common cause of this (across the board) is a failure of the idle air control valve (IAC). this valve controls how much air the engine gets while idling, and if stuck closed will choke off ALL the air to the engine, causing it to stall.
i dealt with this exact problem on a 98 buick yesterday. it was the IAC valve that had a problem, and the computer showed no DTCs

 

Just as Josh says the IAC is the #1 problem with symptoms like this. I've had it happen to a '97 E250 and a '99 E250, both with the 5.4 motors. No codes, stalled or wouldn't idle until the IAC was changed--not even a hiccup since.

 

Thank you, I will definitely be buying that part. By any chance do you all have instructions as to how to change the part out. Thank you again!!!

 

Haven't done it to a ford, but all the ones I have done are easy, find it, mounted to the throttle body in most cases, remove wire harness and 2 mounting screws, and pull it out, thats it.

 

Before you go replacing the IAC valve, you would be wise to try cleaning it if it is indeed the culprit.

Simply unplug it's electrical connector and remove the bolts (not sure how many on your year/model.... but typically 2) and pull it out and give it a good cleaning with spray solvent such as carb cleaner or something similar while scrubbing it out with a brush and working it's little pintle in and out. This treatment often restores proper function to a marginal IAC valve and in my opinion should be a yearly maintenance item. Especially considering how quick and easy it is to perform and the surprising difference it can make on the idle quality of your engine.

This can also help a lot of times with the "hunting" or unstable idle speed on EFI vehicles. (This valve does control the idle speed via it's operation afterall)

If the valve was fried I believe that the computer should be throwing a DTC indicating the open circuit???

In any case, the same treatment can be applied to your EGR valve if the IAC is found to not be the problem as a dirty EGR valve can also cause stalling due to sticking open after you let off the throttle causing the fuel/air charge to be excessively diluted and unable to be burned.

Good luck!!

 

Replace it, cleaning it is temporary, unless you like doing things more than once, I did mine at 90,000 miles and never had another issue.

 

Hey Dustmote--------I've had to replace two of the IAC's and oddly enough they both had never thrown a code. Not sure if that was a glitch in the OBD II system?

The two I changed were both in excess of 100K miles. I preferred changing them out after I knew for certain they were causing my idle problems. Cleaning probably works but like Maples says it might only be temporary unless the budget and time dictate its necessary at the time.

 

To throw a code, it has to be an electrical issue, the problem is that is NEVER the case, they fail from heat, corrosion and debris, just as the EGR fails from carbon build up, yeah, cleaning will get you a few days operation, but I know the trouble of getting the doghouse off, mine is easier that yours due to my handicap power seat base sliding back 2 feet, just replace it and be done. I have been on Ford forums for years, just about everyone tried to save a buck cleaning them, some were suckered enough to do it twice, but the end result was it needed replaced. Codes read faulty electrical circuits, either from the item needing replaced, or down stream, the IAC is receiving a signal, the solenoid is charged, but the plunger is stuck, there is NO probe indicating it's location to sense a fault. When your starter solenoid fails, do you get a code, it's the same principle?

 

Good points Maples!

Naturally the lure of saving the almost $100 for a new Ford OEM part is still there. Were it not for these forums I'd have tried cleaning the IAC but we've seen how its rarely a longer term benefit.

 

During the KOER test, the computer manipulates the IAC in order to check and see if the resulting change in RPM's shows that the valve is working properly doesn't it?

Or else, what would be the reason for the computer to play around with playing around with the IAC at all during the test?

Of course it doesn't set a regular DTC while the vehicle is running in normal mode..... I've got a Ford publication in .PDF format which details the operation and diagnosis of all kinds of sensor and actuator issues with these engines if you would like to see some more about running these tests....

I guess I kind of took it for granted that folks were doing the whole KOEO/KOER/Dynamic Response test rather than just looking for the check engine light during normal operation.

Also for what it's worth, I've gotten 100,000 miles and years of service out of cleaning a dirty and stuck EGR valve.... I used a small toothbrush and some carb cleaner, then lubricated the shaft with 3-in-1 oil and worked it with my finger until it was actuating smoothly.... I realize that the 3-in-1 oil is probably burnt up due to the high temperatures involved, so my thinking was that maybe it would break down to carbon powder and lubricate the shaft in a dry fashion like that special graphite powder that they make for spraying in lock cylinders??? Whether the lube helped or not, I am not sure....

As always, YMMV.

Good luck!

 

As much trouble as it is getting at engine parts, I'd rather replace them, when they hit 100,000 miles, it makes more sense to replace it than trying to see if it'll last forever. I'm all for saving money, but I'll not religiously remove, clean, lube, and replace components when they can be replaced, my time is money.
The ECM does not time the IAC function so it knows it's bad due to increased operation time, there is no sensor to read the flow on either side to see if it's functioning.

 

BTW I have 145,000 miles on my van and it has the factory EGR, when it fails, I'll replace it rather than clean it!

 

Hey Mr Dust is that .pdf file available to share via email? It sounds like a very useful bit of information!

 

I want the program and cable to hook my laptop to my vehicle, I just don't want to pay as much as a used pre-electronic vehicle sells for.