Have a 98 Expedition with a 4.6 out of no where having an issue holing idle. If I hold my foot on the throttle its fine but as soon as I let off it doesn't idle at all it just shuts down. No codes showing. I changed the tps no result. changed fuel filter it was time anyway. and nothing. Fuel pump working fine and I have spark. Its not missing or anything and I can see nothing obvious. so any help would be appreciated. thanks!!

 

probably need to clean the throttle body and the IAC. And the MAF Sensor

 

Replace your idle air control valve. Don't waste your time cleaning it.

 

thanks for the help. that's what ill be doing.

 

new IAC made no difference. still doing exact same thing. help!!!!! please

 

No codes mean it's a process of elimination.

Clean your throttle body and the Mass Air Flow sensor as stated above. 20 bucks and 20 minutes of your time if you know what you're doing.

Disconnect your battery for a few minutes. Amazing how many electrical quirks it cures.

My old Bronco had a fouled O2 sensor and had very similar symptoms.

 

I will give it a shot. thanks

 

Make sure you use the correct cleaner for the correct parts. Do not use carb cleaner on anything. The MAF has a specific cleaner as well as the throttle body.

 

Also be sure your pcv valve isnt stuck.

 

Might be upper intake gasket. Mine would idle up and down in the colder weather, sometimes shut off.