Mechanics

98 WON'T IDLE

1998 Ford Expedition

98 Ford Expedition, 5.4 Automatic 4x4.
The car will barely run at idle. It usually dies. Driving is ok. At a stop I have to keep it at about 1000 RPM to keep it from stalling.
The code scanner says P0171 bank A is running lean, P0174 bank B is running lean.
I have replaced:
Air Filter
Fuel Filter
Fuel Pressure Regulator Valve
Two O2 sensers on the engine side of the catolitic converter
Idle Air Bypass Valve.

Any suggestion or comments would be appreciated.
Avatar
Islandmariner
May 18, 2006.



Does it idle ok when it's cold? If it's only when warm, try testing the EGR. Or try cleaning out what you can of the intake system. (Throttle body, and accompanying vacuum holes) I'm assuming that you pulled the battery after replacing the idle air and o2's, to reset the computer. Sometimes that can make all the difference. Also, does it idle ok in park, and only low idle in gear?

Tiny
Mightymorbo
May 19, 2006.
Thanks for the help. No it does not idle when cold except for about the first 15 seconds. It doesn't idle in gear, park or neutral. Thanks for the segustion on resetting the computer by removing the battery. I assume, disconnecting the battery for about five minutes should be enough. I'll check and clean the air intake. How do you test the EGR? Could it be low fuel pressure? How do I test the fuel pressure?
Thanks again for your help.

Tiny
Islandmariner
May 20, 2006.
Well generally an EGR problem is only when the vehicle is already warm. And unfortunately i'm not familiar with your particular truck, but maybe this link might help a bit. http://autorepair.about.com/cs/troubleshooting/l/aa042603a_10.htm

And yeah, 5-10 minutes with the battery off should be good to make it relearn. Forgot to mention that you wanna let it idle for a few minutes afterwards to let it figure things out.

If it doesn't idle correctly ever, then i'd say it's most likely a vacuum leak, a fuel pressure problem like you said, or an ignition problem.

Fuel pressure can usually be checked at the fuel rail on newer cars, kinda looks like a tire stem. You might be able to borrow a pressure gauge from an auto store. But make sure you get a high PSI fuel one, and not one for a carbuerated engine. (lower psi) You'll have to see if you can find out what it's supposed to be at while running...sometimes you can check it without running the engine, and just putting the key to on to power up the pump. Obviously if it's out of range, and you've replaced the filter and regulator it pretty much leaves the pump or maybe even clogged injectors. Also a possiblity of a pinched fuel line. Did the fuel that came out of the old filter look funky?

Best of luck!

Tiny
Mightymorbo
May 20, 2006.