Hi everyone. I'm new here, and I appreciate this resource. I need it rather badly right now.

Got a 1999 V10 F350 automatic, 109,000 miles. First I will say what's right about it.

Starts right up, never fails.
Idles perfectly, always.
Above 20 MPH, it runs fine.
No CEL, no fault codes.

Now the problem...intermittent off idle stumble that continues up to about 20 MPH, (when this problem first showed up, it was OK after 5 MPH, so its getting worse). Started off doing this occasionally, now up to about 75 percent of the time, again, getting worse. Sometimes accompanied by extremely abrupt shifts, but not always.

So far, I have...changed the fuel filter
cleaned the MAF
drove with MAF disconnected, (this did trigger a fault code,
has since been reset).

Now when I say stumble, I mean a bad one. The engine quits completely but does not die all the way out, it resumes running back at idle speed. If you can manage to horse it up to about 15-20 MPH it runs fine after that, with the exception that it still shifts hard sometimes, but not always. Sometimes if you throw it in neutral and shut it off and restart it while you're still rolling, it "fixes" it, but not always. Sometimes if you take off by stepping on the gas VERY SLOWLY it will go, but not always.

It seems to be worse when cold, but will do it sometimes at operating temperature. A long warmup helps sometimes, but not always. If you throw it in neutral and step on the throttle while its having one of these spells, the engine revs up normally.

Any help at all will be very much appreciated.

 

Have you cleaned the IACV on the back of the throttle body? Checked for vacuum leaks at all?

I would try these first.
-Clean the IACV
-Check out the hose leading from the throttle body to the PCV valve

 

I have conducted a quick inspection of all hoses and they look OK. I will get the hand torch out and check further for vacuum leaks.

I have not cleaned the IACV. It is my understanding that problems involving this valve predominately occur at idle, not slightly off idle where my problem is.

But it may be worth a shot.

Thank you for the advice. Please keep it coming if you think of something else.

 

Check for a dead spot (just off idle) on the TPS.

Check for a sticky IAC valve. If it stays open as the throttle plate opens, it will allow too much air in for the calculated load.

 

I would almost first think TPS throttle position sensor based on how you described it.

 

To all who responded or even looked...thanks very much!

The IAC is a new idea to me, the TPS I've suspected for awhile. I will tear into these just as soon as the temperature goes back above zero, and I will report back.

Anyone else who has had a similar problem or knowledge of this condition, please post it here. I will be checking back often until this is fixed.

Thank again to all!

 

On my '99 V10 F250, I had a vehicle speed sensor go bad which caused abrupt shifts and a screwy speedometer. The VSS is located on the top of the rear axle and a new one was $25 from the dealer.

 

To CapriMikeC:

Hey thanks, that's a good thought. Was wondering, (if you get this reply, still not quite sure how this forum works), did it set off any codes/CEL?

 

No codes, no CEL. It just started rough shifts and erratic speedometer, but only at slower speeds. I figured it out by reading threads on this forum. This is a great place with helpful folks.

 

A faulty VSS will cause weird shifting, but that really doesn't match up well with the OP's symptoms.

Stay on course.

 

Problem appears to be fixed. I hope this will help someone else who is having similar problems.

After much screwing around that didn't seem to be getting me anywhere, I took it to a local shop. The truck finally showed me a little mercy by actually acting up for the mechanic. He had access to Ford service bulletins and figured it out.

Gotta say, I'm purdy fair with a wrench but I never would have found this.

It was the alternator putting out an alternating current ripple to the brain box/sensors that was causing all the trouble, plus the bulletin from Ford said to run new ground wires to the brain.

Not sure if the bad ground caused the diode problem or the other way around.

No matter, seems to be fixed. But oh my aching wallet!

I was told this is a common problem with the older V-10s.

Thanks again to all for the help. You have a very nice forum here.