Yesterday my the while driving the rpm on my 150 van slowly started to increase to the point of over halyway to full throttle. Just made it back home (very quickly) and shut it off. The engine was rebuilt about two years ago and only has abot 20k miles on it. I checked the throttle linkage and butterflies were closed. When I started it back up it's was still almost at full throttle. Today before trying to start it I turned the key several times to and looked for fuel leaks,non found. I started it back up (engine cold) and had a hard time getting it to start, had to depress the gas pedal to keep it running. Normally I start it by just turning the key without pressing the pedal. It smoothed out after about a minute so I checked for vacuum leaks but didn't notice any. The engine continued to warm up and as it did the rpm increased to the point where it flooded out and Quit. Can anyone suggest where to look for the problem I would greatly appreciate any help.

Lon

 

You're throttle position sensor has died. THe computer thinks that the throttle is open that far and pours fuel into the engine. This raises the RPMS. The problem is that when it reaches a certain point and the butterflies are still closed it floods.

 

pfogle
Thanks for the quick reply I thnk I have a spare one I'll go replace and check it out
Lon

 

I have a similar problem, high rpms at idle and overall, probably about 1/4 throttle above what it should be. I had the codes pulled at autozone and two codes relating to the egr came up. Could a bad egr valve be the cause of this excessive idle...makes for tricky driving on ice & snow. Its a '91 5.0L E150

thanks,
jeremy

 

It depends, if the diaphragm inside the EGR valve has ruptured then yes as it's causing a vacuum leak. I'd test the TPS first, if it's still in operating range then it won't set a code. It should have ~.9 volts at the idle position and ~4.5v at wide open throttle (WOT). If it's choppy at all in it's sweep then replace it. You may also have a sticking IAC, which would cause an idle of about 1500rpms.

 

I replaced the IAC a few months ago to try and fix the problem but no such luck. I will look into the TPS.

 

I replaced the tps (which had two wires bare at the base) with a new one from advanced auto parts. Drove the van yesterday for over 40 miles with no problem, then the high RPM problem came back again but not as bad as the last time only about 1/3 full throttle. I stopped the vehicle and removed the battery cable for about a minute , thinking that if the computer was reading a bad sensor it would restart at a low RPM. It didn't work. I was lucky that it restarted without flooding. Any suggestions on where to look next would be appreciated.
Thanks Lon

 

I am a complete novice at testing voltages. Is there an online resource that explains step by step how to test the votage on the TPS? Thanks!

 

Also, is there a way to test if the egr is responsible for the leak by removing it and blocking off the opening on the engine?

 

Vacuum leaks usually kill idle speed-not over rev an engine. RPM is controlled electronically, opening the butterfly doesn't rev an EFI motor, the fuel is injected, not drawn in under vacuum.

I've grown to respect the onboard diagnostics & got my own fault code reader. AZ & ADV parts stores could not pull codes, gave me a song & dance that the check engine light had to be lit. My $30 Equus digital code reader, bought on eBay, recently ferreted out the TPS that I had dismissed b/c it was fairly new replacement. The maddening intermittent symptoms were dramatically different from when the TPS had failed before. I destroyed the faulty TPS & confirmed the bad internal connection.

These simple code readers initiate test series, 1st with a warmed up motor, not running, but w/key on to check a large number of components & values. The 2nd test requires the motor to be running which can be a challenge if your symptoms include stalling or over revving. In my case a TPS code showed in each test. Not suggesting your problem is the TPS, just recommending the value of having your own fault code reader & drawing attention to the diagnostic software in the FORD computer.