Closed loop stall? Hanging/high idle? Miss?

Any ideas would be appreciated to help me diagnose and finally fix this thing. It's been running well and I just live with it. I've had this car about 12 years now and it's always stumbled some here and there. I can live with it, but if it's fixable, let's get it gone! It has a PC1 ('86) ECU and a set of cleaned/flowed brown tops. Runs strong.

- High hanging idle, 1.5k to 2k rpm. Usually will go down or go away if I goose the throttle. Happens more often, by far, when hot than when cold.
- Slight stumble/miss when hot, seemingly more when hanging high idle, seemingly less tumbles when in what I call the normal 900 range or so.
- STALL if I go heavy throttle above 3k rpm and then let off the gas. Starts right back up. Doesn't stall if I go past 3k, and then coast back down a few seconds before taking it out of gear.

I did a half ass job cleaning the VAM a while back. No change
Cleaned the IAC, then replaced the IAC, no change.
Reset the TPS, got a new TPS and reset it, no change.

Any other ideas? Some thoughts:

I've never checked the throttle plate in the TB, there is some slop in the throttle cable. I could probably pull and thoroughly clean the VAM, and redo the TPS again. I still have an OE dual fuel pump setup.

Any codes? Does it do these things only when warm/hot?

Did you replace the IAC with a Motorcraft unit or some aftermarket POS? It is well known that Motorcraft IAC's are the only ones that work correctly.

Cleaning the TB around the throttle plate may help.

I have had the best results with my old Fords by unplugging the IAC and using the throttle stop screw to st the hot no load idle speed around 100 RPM below the PCM's "target" idle speed of 1000 RPM, plugging in the IAC, and clearing the PCM's KAM by running the codes and clearing them by disconnecting the STI while code are being outputted.

Also be ure the closed throttle TPS volts are under 1.0 V.

The idle will hang when cold, but does it almost all the time once hot. A high rev then stall in coasting only happens after being under load. Revving parked won't stall.

No codes in the past but I just ran both. KOEO 11, and a KOER 25, 77 (my KO is unplugged and I didn't open the throttle during test)

Sounds like at the very least I should do more careful cleaning and try the TPS setting for a third time Is there any chance it's something out of ordinary like the MAP/BARO sensor or something? Anyway I can check for healthy operation? The only thing I would like to throw at it right now would be a fuel pump upgrade, but I would like to sort these small issues out first...

sounds like mixture issues. i'd look at your coolant temp sensor. obviously not the one that displays temp on the dash, but the one for the PCM. make sure you order one for an 86, if you decide to replace it. i don't know if theres any difference, but i'd still get one for the PCM your using. what TFI module do you have in there? base timing setting? plug gap and type? ever had the intake manifold off? check for vac leaks at seals and vac lines, especially ones that go to sensors and the FPR.

-J0N

Only way to check the BARO is to use a DMM that reads frequency. BARO output is a square wave with about 5 V amplitude. At sea level pressure output should be right round 159 Hertz. Freq drops with altitude. With 20" or so vacuum applied to the BARO freq is around 90 Hz.

All good thoughts, thanks!!

My temp sensor is a motorcraft, replaced it already before, but it was listed for the 84. Both 84 and 86 ECTs looks to be the same motorcraft DY1145 according to rockauto.

TFI is motorcraft, as is the rest of the ignition, all new motorcraft. Timing is at 12deg or so, I believe. Plugs are motorcraft, don't remember the gap, should probably check, it's been a while.

Upper intake has been off before, when I put in the Kirban AFPR a few years back after the original one failed. This is also why I was kinda thinking fuel pump(s) may not be helping the issue.

What was wrong with it did you ever find out?

Did you ever figure out the problom i have having about the same exact issues

Reading back through trying to remember everything, sorry for the slow reply.

I went ahead with the fuel pump upgrade to an inline Walboro 255HP, keeping the original in-tank pump for dual pump setup. That's the only change I recollect. I don't think it stumbles and dies as much as it used to from a high rpm throttle lift, but the occasional miss has never fully gone away. The only other thing that's changed was replacing some lengths of wire that had dissolving insulation near the TFI pigtail shielding, particularly, the SPOUT wire was pretty much toast. Trimmed the loom and shielding back an inch or two and spliced in fresh. This had to have been a year to two years ago, I haven't put hardly any miles on the bird in that time.

It runs the smoothest now that it ever has since I've owned it. But of course, it's now developed a pretty serious oil leak *facepalm* also needs new clutch and tires. lol