Recently, my truck has been revving around 1500 rpm in neutral and park and it runs on after letting off the gas (almost like a jet engine). The gas mileage went from ~220 miles on a tank to ~160 miles a tank. Its a 93 150 with the 5.0 Vacuum leak isn't it I don't believe because it did the same thing last winter, but stopped spring and summer only to return the last 2 weeks. Any common causes? MAP censor was replaced by ford this summer and I tried a new IAC last winter to no avail. Any suggestions on where to start? Throttle body is clean by the way.

 

Have you tried cleaning the throttle positioning sensor...

 

Error code scans! https://www.f150forum.com/f10/how-re...es-obdi-10907/
Also check for throttle cable bind & lube it.

 

It has a new TPS sensor from last spring and the cable seems to operate smoothly. Gonna try the code scan today

 

Also. clean & test your IAC. http://www.fordfuelinjection.com/?p=39

 

Im having the same problem, but mine is a 5sp manual. Sometimes when i pull up o a stoplight and push the clutch in the rpms go up until i blip the gas pedal then sometimes it comes back down to idle. This is a pain when it happens everytime i push in the clutch that it high revs. I have replace the throttle cable, IAC, and the TPS. I have aslo cleaned the throttle body and lubricated all of the linkages. If i shut the truck off going down the road and then turn it back on, it will go away until i restart the truck. Its like im reseting something then its all good. The only codes i get are for the egr valve. I am also getting around 10-12mpg. I am replacing the injectors next week. I have a couple thats cracked on the metal cone on the end.

 

IAC is new, throttle body is clean, TPS sensor is new. only thing I can think is something binding, but I haven't found anything yet. It isn't throwing any codes either. I feel like I'm on a wild goose chase

 

It doesn't drop when you tap the accelerator?

 

Nope doesn't stop. No codes still, and its weird, it will do it one day and then didn't do it at all Saturday and then started doing it again Sunday and today.

 

Fuel pressure regulator??? At idle pull the vacuum of of the regulator. If rpms go up then it should be ok. Also check to see if there is gas in the vacuum line. There should not be.