This has me stumped. I've been a backyard mechanic for years (really decades), prefer older vehicles that I can still work on, and have a pretty good track record.

This is a 1988 full size Bronco with a 5.8 L gas engine. It's run very well for years and years, with the usual minor maintenance and repair. This past summer it stated surging at idle, just now and then. The "Check Engine" light might come on, but would go off after a while. Then it starting surging more and more, and got to the point of annoyance. I pulled the codes: TP over voltage and bad HEGO. I replaced the oxygen sensor with an OEM Bosch. No help.

I gave in and took the Bronco to a local shop. They could not get any codes to come up, although it did surge a couple of times. With my agreement (and a few hundred bucks), they "cleaned" the fuel system from tank to injectors. They cleaned the air intake. Their report to me was the idle air control valve was gummed up and sticking. They cleaned it and declared it fixed. Well, if it were I wouldn't be writing this.

So, in the last few weeks I've purchased and installed:
a) Idle Air Control Valve
b) MAP sensor
c) new plugs, wires, distributor cap and rotor (why not?)

I've read and reread the manauls. I've gone through the inputs and outputs of the EEC-IV in my head. It seems I've covered most of the sensors. I think my next step is to unplug and clean all connectors.

All ideas, coments and magical sayings appreciated; thanks.

 

I would look closer at the TP overvoltage code that initially triggered. Thats the throttle positioning sensor mounted on the bottom of the throttle body. It tells the computer the relative position of the throttle plates and the computer adjusts spark timing and fuel/air mixture according to the reading it gets. If the voltage reading its getting from the TP sensor is beyond the predetermined parameters the computer "gets confused" and this can definitely cause the surging problem you are having. TP sensors are basically variable resistors and with age their resistance value changes eventually causing their failure.

 

Woody...if you do find a fix for it, please please please let us know. This idle surge is an elusive beast that many have been trying to tame. I've been able to make mine better, but not totally go away. Check out this thread that was started:

https://www.ford-trucks.com/forums/s...ht=idle+surge+

 

ditto woody...check the TPS. Cleared my problem with an '88 302

 

Same here, try the Throttle Position Sensor, made my 88 Bronco 302 stop surging also.

 

I just checked my records too...it cleared my C.E. light as well.