4.0 OHV high idle problem

[boostranger]

ok i have 91 xlt auto and i've been chaseing this high idle for a while now, started out only when i was on the highway with the cruise on, if i stopped and put it in park it would idle at around 1500 rpm. but it has recently started to happen any time i put it in gear and drive it more than a couple blocks and then stop and put it in park it will sometimes idle as high as 1800 rpm, i have checked and replaced the IAC, cleaned the MAF, checked TPS and its at .93 volts, no vacuum leaks, replaced upper and lower intake as well as injector o- rings. it idles fine when first started and sometimes it will go for a few days without doing it. I am about tird of haseing it, anyone have any ides?

 

[Glacier991]

Certainly has the earmarks of a TPS problem or a vacuum leak.. things you checked. I wonder if the tps could be hanging up.

 

[boostranger]

possible ... i have a few sitting around ... might change it in the morn and see what happens

 

[Rhett]

Sounds like you are on the right track. Also check the throttle body for deposit buildup. Maybe the throttle plate is sticking open.

 

[91nut]

Same Problem

I had or have the same problem that happens once in awhile. Three years ago I changed the intake gasket (possible leak) and the mechanic who did it told me that Ford's intake manifolds from the 1991 have a tendency to warp over time. He was an ex-Ford mechanic for 10 years. Let me know if you find something different.
Joey