BimmerM3_inGA

Forgive me if this topic has been covered already. I did a search but didn't find any matches for the particular problem I'm having. I found some that were similar, but nobody seemed to be having the exact same symptoms.

Anyway, I've been turning wrenches on BMWs for years, but never a Ford. This is my brother's vehicle and I'm trying to help him out because his wife is supposed to be having a baby on Monday.

Here's the situation: The vehicle is a 1997 Expedition with the 5.4 liter engine and about 170K miles. When started, it will immediately rev to about 2000rpm and then die. If I keep it revved up, it'll stay running but if I let the revs drop it will sputter and die. Sometimes it will hang at around 250rpm and backfire a little before dying. If I can keep it running long enough to get onto the road, it will run fine at highway speeds. But if I lift to slow down, it'll stall. Letting it warm up completely doesn't seem to make any difference.

What I've tried so far: Replaced the fuel filter; no difference. I can hear the fuel pump running and cleaned the MAF sensor. I checked for OBD-II error codes and none have been recorded and the Check Engine light is not coming on.

I am suspicious of the idle air control valve since a malfunctioning one can cause similar problems with a BMW. I checked the voltage going to the valve and it's 11.86v. Next, I checked the resistance across the terminals on the valve and it was 9.1ohms (in the middle of the spec range of 6.0 - 13.0 ohms). It looked a little dirty inside, so I cleaned it out with some electronics cleaner. I noticed that with no voltage going to it, there is a gap of about 3mm between the valve and its seat. Next, I applied 12v to the terminals and the valve responded by making clicking noises and I could feel something inside moving. But the visible portion of the valve wasn't moving. Should it be?

Can somebody explain how the idle air control valve is supposed to operate? Does my story describe abnormal operation? Needless to say, we don't want to just throw money at the problem until it goes away. If a new IACV will fix it, no problem. But I don't want to buy one just to see if it helps.

Any advice or suggestions would be most appreciated.

 

BimmerM3_inGA

Update: I replaced the IACV with a brand new one. No change whatsoever. I was convinced that would fix it right up.

This really has me stumped!

00gtr1

Do you hear any vacuum leaks? high mileage 5.4 pcv hoses like to deteriorate and cause a vacuum leak at the pcv valve or at the back of the intake. Does your scan tool show what your fuel trims are doing at idle? do you have a gauge to check fuel pressure? should be 30-35 psi. see what it does under a load. but after looking at your concern again I'd say you have some type of vacuum leak.

BimmerM3_inGA

And the winner is...

A loose hose! A friend came by this morning and put a set of fresh eyeballs on it. Within 5 minutes of popping the hood, he found the culprit. There is a black rubber elbow that connects to the back of the intake manifold just below the IACV. He put it back on and added a zip tie for good measure. It purrs like a kitten now.

I've been tearing my hair out for 2 days and it was literally a 5 minute fix. My bud was a little disappointed that it was so easy. He was all psyched up to change a fuel pump.

Needless to say, I'm just glad it's done! Thanks for all the tips and suggestions!