Great forum, guys.

I have a 89 F150 4x4 and have had some idle problems and doggy. Just not running right.

I pulled the codes both thru a vohm meter and also did the engine light thing and kept coming up with these.

One is 22 and it says low MAP or BP volts and the other is 122 which says TP sensor is low voltage.

Any ideas if this would make for low idel and porr mileage and sluggish?

Someone said try the IAC first and it may not code. All these things are 17 years old. I bought the truck new.

Any info would be appreciated. I cleaned the IAC and a few months ago replaced the TP sensor...from Autozone.

Thanks for any info I can get...been a good truck.

 

Yes, it could explain poor mileage. I believe this is a speed density system. Newer trucks use a Mass Air Flow (MAF) sensor to measure the incoming air and inject the correct amount of fuel for that amount of air. These trucks measured the manifold absolute pressure (MAP) and RPM. Knowing that and the specifics of the engine (displacement and volumetric efficiency), they can calculate the air flow and then use that to calculate fuel required.

These two signals probably both require the regulated 5V from the computer. If the wiring from the 5V is open or the either wire is shorted to ground, it could cause this. I'd start with a thorough visual examination of the wiring and connections. In the wire look for bare wire, oily wire, bubbles in the insulation, etc.

 

Thanks for the response. My other question is even though the IAC is not throwing a code...some tell me to just replace it because after being so old it should be changed just to make sure and more times than not, the engine won't throw a code for it.

I have not put hardly any sensors or anything else on this truck for 16 years...just good maintenance of filters, pvc valves, etc. Guess I can put a few bucks in to it...maybe even a new 02 Sensor!

The code 22 seems to mean just replace it? I do not think mine is adjustable...so when it is showing a low voltage signal I don't think I can raise it by adjustement...or can I?

Thanks, any other input is appreciated.

 

Jeff,

Your 89 should be all 2-digit codes, no 3-digit ones (they were introduced around 1993). You might want to re-run the codes.

If you are getting a MAP code, then either there is a fault in the vacuum line or the sensor has gone bad.

The IAC is responsible for idle speed management. Given its age, I'd suggest replacement.

Steve

 

Steve, thanks for the info on the 2 codes vs 3. I did it over and over and it seems hard to read...the 22 are pretty clear with the pauses but the 2nd code which is what I thought was 122 could be 32? I plan on doing it again on Friday. I did the vohm meter and the engine light.

I do think it may be worth my money to spend the $66 to have it read from a Ford dealer...our dealer is pretty darn decent and fair.

Would a person be smart buying on of the better code readers?...wonder which one can be counted on to work right.

Thanks for the info....let em know if there are any shortcuts or info that can help read these things.