Hi all it’s been a very long time on here.lm trying to repair My 1986 Bullnose 5.0 mfi. My second driver.
My question: proper curb idle adjustments. I do know it’s been messed with😎 The rpm,s take off very very high when first started hot or cold. 30 seconds later rpm,s return to an expectable level. I’ve messed with set it a few years ago w/ no luck. I believe the timing is set (I’ll have to recheck). New idle air valve. No vacuum leaks. I think I checked and replaced the TPS. It’s been a couple of years. Will check for DTC,s. I’ve read that the ECM. controls the idle circuit. ANY THOUGHTS 💁. I’ve got to get this repaired the main bearings don’t like the very high rpm,s (knock)😂 It’s my daily driver now. My other truck needs head gaskets. Thanks for listening.
Its been a while since I messed with these systems and for good reason, from what I remember the butterfly valves should be essentially closed or just slightly open as at idle the IAC is controlling idle speed. If the butterfly valves were cranked open then it will be like holding the throttle open. What you can do is turn the stop screw to allow the plates to close more if they are cranked open some. One problem you may run into how ever is having to adjust the TPS as it may go below minimum voltage for the system and may or may not throw a code for TPS low voltage.
Since you cant read live data from OBD I systems you will have to back probe the wire going to the ECM for the voltage return and loosen the TPS and rotate it till it is above minimum value then lock it in place.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2