high rpm

[Nhaz]

Ok I will try to make this short. its not but I I'll try.

When my truck gets to up the operating temperature the rpm goes up to 3k. the first mechanic i took this too told me the error code was 22 which is the Map sensor.

I went over that engine compartment very carefully .. there isn't a map sensor on that truck that i could find.

so I brought it to another mechanic with the story. he siad he would find the map sensor and that the ford people had possible hid it under the intake manifold or under the air box. so. i went and got a map sensor for the truck since the auto parts store listed one for it.

Got back and the mechanic also swore up and down there wasn't a map sensor on that truck.

Now once he had definably determined that there was no map sensor he pinned down the problem in under 4 minutes. he took the wire off the computer controlled choke on the front of the intake and the idle dropped right back to 600 rpm.

he tells me up front that theres nothing wrong with this choke and that the computer is telling the choke to turn on all the time.

And the quick dirty fix was to put in a dash mounted switch to manually control the choke and take the computer out of the loop.

He also told me that he has a f150 that also doesn't have a map sensor never did and reports the exact same code.

Now the question is. what is the underlying problem which is telling the computer to turn the choke on all the time?

 

[constant_projecttruck]

my old 92 4.0 did that all the time. It was only on startup and I would just redline it for 3 to 5 seconds and then it would drop back to normal 750 to 1000. Although when it was less than 0 degrees celcius it would stay high. My coolant temperature sensor and sending unit were both bad so I replaced those and the 3 weeks I had it after that it never idled high again.