just went and started the bronco this morning and it reved all the way up to 3000 and has not came down for 25 miles of driving. i figured putting it in gear would eventually drop what its doing but no, after all that it still does it.

i checked all the obvious. fuses are all good, IAC is brand new 2 weeks ago, sprayed all gaskets on intake, sprayed all vacuum lines.

it was a perfectly running truck friday night, but now on monday morning it doesn't work worth a ****.

my work suggested it was probably a bad computer. i dunno what to do. i can't drive it like this. i don't want to turn into a toyota accident scene.

help is greatly appreciated. 1989 ford bronco xlt 5.0 AOD trans and manual 4X4

 

PULL CODES

possibly the IAC, TPS or the throttle body/cable are freezing up.

 

i just started it up again at 5:25 and it worked fine. dunno why there was such a huge fluke today. dad came over and looked at it and it didn't act up.

still reads the 3 codes it has always had since last summer. 2 are nonsense and the other says fault but no definite location

do these trucks memorize the amount of starts between computer resets and tests?

 

What are the codes? Tell us the numbers you are getting... they aren't nonsense. Each one has a specific meaning. Each code is either two-digits or three-digits. The ONLY code that is a "passing grade" is code 11 or 111. (And your truck will either give two-digit OR three-digit codes not a mix of both.) Everything else is potentially a problem and needs to be dealt with. Run KOEO test first since you don't seem to have idle control. KOER test cannot be performed properly without idle control anyway.

And yes, the computer keeps count of the number of times the engine is started. KO (Key On)

 

i think i remember 31, 68, 21

where is the site i look these up on?

 

code 31-PFE circuit is below minimum, 21-ECT out of range, 68- AXOD trans temp switch open

 

Code 31 indicates that the EVP sensor showed a lower-than-expected voltage at pin 27 of the ECM. There IS NO PFE sensor in the Bronco. This is typically caused by either faulty wiring, poor connection at the sensor or a failed EVP sensor. There is a way to test the wiring if you need the procedure, let me know.

Code 21 indicates the engine was either too cold or too hot when the self test was administered. If you are certain the truck was at normal operating temp during the test, make certain you have +5VDC at the VREf terminal of the ECM (Pin 26) with the key on.

Code 68 is a code unique to the 1.9L, 2.5L, and 3.8L engines. It indicates absolutely NOTHING in the Bronco and will not even be generated in a Bronco ECM.

I would think it is far more likely that you got Code 67 which indicates that the air conditioning was not turned off during the KOEO test. Otherwise Code 67 only appears in the KOER test on trucks equipped with the E4OD and its a "terminal" code indicating mass failure of the transmission electronics.

Given these three Codes, your problem is rooted in the first one (Code 31). The ECM is hunting for control of the EGR system and failing that, it simply defaults. With the RPM's as high as you say, the FIRST thing I would check is the vacuum control line from the TAB solenoid around to the EGR valve. Your description would indicate not only a loss of EGR system control but an open vacuum source as well.

The other two Codes were most likely generated because the KOEO and KOER tests were not administered properly. Make certain you have the truck at normal operating temperature and that all of the electrical accessories are OFF when the test is administered. During the KOER test you must perform the "goose" test or it will generate a fault code as well.