I have an 86 Bronco 302EFI with AOD with 214,000 mi. Nothing replaced.I had a really low idle, I cleaned the airbypass valve. Then I had a really high idle, especially when starting cold. I then replaced the air bypass valve with a new Borg Warner. The high idle persists. I replaced the throttle position sensor and cleaned the throttle body. Still high idle. I read the codes and got a 31. I replaced the EGR valve and sensor. Read the codes again. KOEO 11 and KOER 13. Still a high idle. The only thing I haven't replaced is the O2 sensor. Any ideas?


Steve

 

Not sure this is the answer but....I had the same problem on my 88. I replaced the temperature sensor and my problem went away. My theory was that the temp sensor was tricking the computer into thinking it was really cold and needed to keep a high-speed idle going.

 

I'll be interested in what you come up with..... I've replaced the same parts, including the O2 sensor, on my '85..... my problem is more of an annoyance - when slowing to a red light, I'll push the clutch in, and the truck will rev up to 1200 rpm. After about five seconds of this, the truck will go into that lovely idle surge I'm sure all of us first generation EFI owners are familiar with. I can pat the gas and it will immediately idle down to 750-800 rpm and stay there, no questions asked, until I leave for the next light. I only noticed this after cleaning (and then replacing) the air bypass valve, though it could be unrelated. I have also, in the course of rebuilding the truck, replaced the EGR valve and gasket, the throttle position sensor, both upper and lower intake gaskets, throttle cable, kept it completely tuned up (including O2), and to the best of my searching believe it has no vacuum leaks. I heard the temp sensor can go and cause problems, yet still be operational, so I bought one, but haven't replaced it.... only around $17.00 aftermarket. Question - can timing chain slack cause something like this? With 142K miles, I can picture mine having slack, and perhaps varying cam timing under load versus at idle? Replacing this is on my to-do list, also, but so is a new engine at some point!