So I just bought an 88 F-250 4x4, 351w and a C6. I test drove it and it ran fine, drove it home about 100 miles, no problem.

The next day I drive it down the street and it stalls when I bring it to a stop, right where the tranny downshifts into 1st. I drive it some more and it does the same thing. Once it's fully warm (about 15 miles or so) it runs fine, and the rest of the day it doesn't stall out when you stop.

However, between 10-20 miles from initial start it then wants to stall out when you press the gas pedal when leaving from a stop. Again, after you have driven about 20 miles it stops, and runs fine the rest of the day.

To recap - cold start to 10 miles it stalls when you bring it to a stop, 10-15 miles it stalls when you stop and leave from a stop, 15-20 miles it stalls when you leave from a stop, 20 miles on runs great.

Looks like the EGR valve and the idle control motor have both been replaced.

Any ideas?

 

Ford Fuel Injection How To Run a Self-Test Here is a link on how to check for trouble codes. Might be worth doing.
Also on that site it will tell you how to check the Engine Coolant Temperature sensor, might be worth checking that also.

 

Definitely worth doing! & one of these are definitely worth buying (digital numeric display w/ memory). http://www.handsontools.com/Equus-In...ol_p_5574.html

Is your engine Carbed or EFI?

 

It's EFI. I took the wiring off the IAC and it's looking a little frayed, and was twisted around and may have been shorting out. I straightened it out and just took the truck out (I have only driven the truck about 2 miles today) and it didn't display any of the aforementioned symptoms.

 

Heres how you test the IAC/IAB: Ford Fuel Injection Idle Air Bypass (IAB)

 

Well, I still been experiencing the problems listed above, but they aren't quite as bad now that I'm not using the AC. I worked on it some yesterday, and discovered a couple of things that might be the problem. The vacuum modulator on the tranmission was leaking, and all the lines connected to it all the way to the engine had very loose connections due to the trans fluid swelling the rubber. Furthermore, the PO had clamped the connection at the engine (due to the loose fit) and the vac line was almost cut in half at the clamp. On top of this, there was a cap on one of the manifold fittings at the vacuum tree that was the wrong size.

So I just went outside and replaced all the suspect parts with good ones. I think this could be the source of both problem. We'll find out in a couple of hours, as I am changing the rear diff fluid and once done with that I can take it on a test drive.

 

Thought I'd update now that I again have potentially found the problem(s). My valve cover gaskets were leaking, and I decided to put some shorty headers on the truck. Turns out both were good decisions. When I took the upper manifold off the engine, I discovered a couple of bolts were loose, I think this was causing a vacuum leak that might have been my stalling problem (leak was worse when warming up due to the expansion rates of the metals opening up the gap a little more until the temps equalized on both side of the manifold.) Plus while installing the headers I discovered about 1/2 the bolts were loose, 3 were missing, and the EGR tube was cracked in 1/2.

I fixed everything, replaced the EGR tube, got it all put back together, and it ran fine without stalling where it normally would have.