97 Expo won't stay running. Could it be the IACV?
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.