From "Ford Fuel Injection - How to Understand, Service, and Modify" Troubleshooting chapter.
What is interesting is the terminology. From 88-92 The term was ISC (Idle Speed Control)
But from 1993 on the terminology was changed to IAC (Idle Air Control)
The two columns on the left are the order of which things to check first. MECS is "MAZDA ELECTRONIC CONTROL SYSTEM"
"Quick Test" means pull codes by running EECIV self diagnostics.
Note that Andy's suggestion of a fuel quality issue is not outside of the realm of possibility.
A few days ago out of curiosity I Googled "EECIV stumble on cold idle".
That brought up the longest list of posts and threads I've seen from any problem issue search I've done. It covered many Ford models.
This kind of issue has been experienced by a truly large number of frustrated owners, seemingly from the posts without ultimate resolution, despite often AtoZ parts replacings.
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Ed, you make it all sound so hopeless. What do you do? Just buy a new Scorpio when yours breaks down?
Such poor success rate is easily attributable to several factors.
In the first place most folks "plea for a solution" but never get around to reporting their resolution to the problem.
In the second place, many folks don't have very good troubleshooting skills. Case in point - I am surprised to observe how many can't even use a multi meter properly!
You should read the posts I referred to. All of them.
My experience with random SSHIS was on my '88; after I replaced its engine for the one in my parts car (a 100K mile runner with a really strong engine) I haven't experienced another SSHIS episode in it. Of course prior to that I did everything you would have done to identify the cause, without finding anything to explain it. On IMON a few speculated distributor shaft wear might distort the PIP signal so that was on my mind in deciding to install the parts car engine.
It's true and frustrating that peeps might not report on how they resolved, if they did, head scratching issues.
I've posted about how after the engine change above SSHIS hasn't recurred, to date. No one else with this issue has reported it "resolved".
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
My AC20 Idle air control valve arrived this evening.
It is made in China. No surprise here.
I did not notice any discernable difference between my old valve and this one. Other than the side entry ports are a little bigger.
I measured resistance across the solenoid and I measured 10.8 ohms in both polarities. There was no diode stamping on this valve and my ohm measurement bears this out. Neither was there a diode in my original valve and it measured 11 ohms.
The only thing I see different between AC20 and AC22 (at least from Standard Motor Products Catalog) is that the AC20 comes with a new gasket and AC22 does not. The new gasket is a bit thicker that my old gasket.
In any case I installed it on the car (using the new gasket). Fired up the car and my hesitation problem is now gone.
Hurray!
Ed - I know that seems like a generic kitchen list, but had I followed it initially I would have not have changed the ECT, ACT. They are not even on the list!
From prior experience with a failed ECT and the fact that the problem had a temperature related aspect I thought for sure it would have been one of those items.
I suspect your original IAC valve/valve seat had carbon deposits that didn't dissolve from your cleaning. You might disprove that by using your flexible boroscope. I found that cleaning the IAC is always more than spritzing brake cleaner in it, covering the holes, and shake shake shake. That pretty well cleans carbon from the chambers but may not loosen deposits on the valve seat or valve head.
I've not seen weak IAC solenoid or valve springs so far. Given how critical a good seating valve is I depress it and spritz cleaner on it/its seat multiple times. Maybe you did that. Maybe it needed even more of that.
At this point it's academic since the new unit solved the problem.
My eraser is at hand if after a couple more cold starts with no stumble to say Sayonara to DSOCI
syndrome.
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
I don't know. I haven't thrown the old one away. But it's going on 35 years old.
I guess it has some sort of hard polymer seat on the valve? How long can that last? Especially considering the ever increasing alcohol they have been adding to the gasoline since 1988?
Not sure how long the "Premium - Made in China" valve will last. But one could at least hope that some sort of accommodation of high ethanol fuel has been built into it.
Early winter-like temps now shiver the timbers in Hatboro and most parts of the country. So, your audience (me) is eager to know if installing the AC20 eliminated acceleration stumble. We know it aced cold start, but how about while driving before the engine warms up fully which is definitive.
YMMV
P.S. Nice spanking given by the Commanders to the Eagles last night.
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
I searched wide and deep for any difference between AC20/22. SMP catalog for AC20 is ~45 internet pages with no listing for Merkur(s). SMP catalog for AC22 is 20 pages with Merkurs on the last page.
Only PepBoys has product info on AC22, related to the magnet:
Screenshot_20221115-084115_Chrome.jpg (367.92 KiB) Viewed 2333 times
I found nothing, anywhere, re AC20 magnet.
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Not sure why you are digging this old topic up again.
The AC20 works fine Ed. The only difference I saw in the catalog was that one comes with a gasket and the other does not.
I saw no outstanding differences between AC20 and the stock solenoid, including measuring the resistance of the coils.
It's just a simple valve. The ECU controls it via closed loop and PWM. So even if there was some sort of variance between solenoid valves the ECU would automatically compensate.
The solenoid could be different in some way. Or the spring. Or the pintle and seat coatings.
Even selected Rangers and Broncos with the 2.9 of 88-90 period call for AC20 in the SMP catalog. Why not the AC22? Is the included gasket special in some way?
Have you operated your Scorpio in recent cooler temps, not just starting but also driving until warmed up?
I want to know definitively. What you pointed out I observed and tested for myself years ago on my stash of almost a dozen from JYs or parts cars. But you also noted the bores were a bit larger on the AC20 IIRC. Why?
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Well, at least to where it seems to be the latest situation. Since my XR4 is down for the time being and each cars shares the same idle valve, it's going to be a swap-for-test candidate.
1987 XR4Ti with about 62,000 miles, Azure Blue.
T-5, Mustang front brakes, T-bird rear disks
mc2racing: full/new suspension and all bushings.
stock turbo, T-bird VAM and LA2, ~ 15-17 lbs boost, Rapido intercooler
40-Bob log header, full 3" exhaust
But I don't think you understand the very simple operation of the device and how wide a tolerance there is.
It's just a bypass around the butterflys. If the port was slightly larger or smaller the ECU will just set a different PWM value in order to maintain the idle where it wants. It's working range is a something like 300 rpm so it's not a big deal.
You seem to think it is some sort of esoteric and highly calibrated carburetor jet...or something...and it isn't.
Joe62Tampa wrote: ↑Thu Nov 17, 2022 2:39 pm
Some aspects of this seem to overlap with my posting of "Dr. Jekyll... rough running",
Joe study table 8 post above. Follow the steps from top to bottom.
Make sure the EGR valve is not stuck open as it will then behave as a vacuum leak. It is possible it may stick when cold and frees up as the car warms up.
A quick check is too feel the pipe from EGR to throttle body. If it gets hot right away after starting the car while idling then it is leaking.
It is very easy to have a "user installed" vacuum leak where the EGR tube attaches to the throttle body.
If you need to replace EGR then make sure you get the more expensive STANDARD MOTOR PRODUCTS EGV271 and not the T-series garbage one.
