Hi all, looking for some thoughts on a problem I am going nuts over. At start, Bronco will hit 1500 rpms and immediately drop to about 1000. Once warm, the idle hunts between 500-1000 RPMs.

I've been working on this rig for almost a year fixing half a dozen codes and I can't seem to work this one out. I've replaced the EGR and EVP, TPS module, tested and cleaned the IAC (no bypass added), cleaned and cleared throttle body, replaced the neutral safety switch.

I only have one code 67 Neutral Safety Switch. I'm tracing that down still.

Anyone have any suggestions on what to test, where to go from here for the idle issue?

 

Have you checked to be certain that the throttle plate stop screw has not been tampered with? The RPM's you are talking about sound a touch on the high side for normal idle. There is a method for resetting the stop screw if you need the info, let me know.

 

I'm not sure what the stock position of the idle screw looks like but it appears to me to be screwed in some. There are only about 2-3 threads on the right side of screw. Would that have somethign to do with it hunting? I know the idle screws aren't supposed to be messed with, just no sure if the screw would be the cause of hunting or if it was an attempt to cure the symptom by the previous owner.

 

The common incorrect fix for a dead or dying IAC is to run the screw in enough that it holds the throttle butterflies open a bit. While this works to keep the truck from dying until the IAC can be properly replaced, it screws with the computer's ability to control fuel-air ratios at idle and consequently, it spends a lot of time calculating because more air is present than it is "expecting" to see due to the throttle being propped open.

IF the IAC is functioning properly AND you disconnect it from the wiring harness with the engine running, the engine should wind down and die within about 2-3 seconds. If it doesn't, the throttle screw needs to be reset.

 

Well, I need to put this issue on hold. I now have a NO START CONDITION. No spark so Coil tested bad, repalced, still No Spark. Checked voltage and ground at the ICM and it's good there. Signal switching to coil failed, PIP failed. I need to pull the distributor. Does the signal switching failure mean a bad ICM or does it just point you to the PIP. So many details I've read the last few days on this I'm confusing myself. Voltage is test 1, Ground is test 2, Signal Switching is test 3, PIP is 4. My thought is that it just points you to the PIP.

 

Rebuild entire distributor and replace the ICM, the fail of one leads to the fail of the other, it's a cycle, Rebuild complete is the solution.