Sudden Intermittent High Idle

[DPDISXR4Ti]

I'm still a firm believer that what you call "Sudden Intermittent High Idle" is simply the EECIV going into limp mode.

I agree. The PCM programming is saying, "I didn't like that input (or lack thereof) - better idle up to make sure the engine keeps running"

Next time it happens Brad, and while the engine is idling high, pull over to the side of the road and turn off the engine, wait a moment and the restart. If the idle goes back to normal then it's definitely limp mode.

That's exactly what I've done and that's exactly what happens.

[Ed Lijewski]

I'm still a firm believer that what you call "Sudden Intermittent High Idle" is simply the EECIV going into limp mode.

I agree. The PCM programming is saying, "I didn't like that input (or lack thereof) - better idle up to make sure the engine keeps running"

Next time it happens Brad, and while the engine is idling high, pull over to the side of the road and turn off the engine, wait a moment and the restart. If the idle goes back to normal then it's definitely limp mode.

That's exactly what I've done and that's exactly what happens.

'Splain why when the sudden high idle occurs the computer doesn't set the Check Engine light on the Scorpios.

And from what I've read so far re other Ford EECIVs, where the sudden high idle occurred, no Check Engine lights were set.

On each of my Scorpios on rare occasions while under power the CEL would illuminate, then after shut down and restart the CEL remained unlit. So, in those instances the ECU detected and responded to an anomaly, and during restart confirmed everything was AOK .

So the EECIV should illuminate the CEL as high idle episodes occur.

YMMV

[brokencase]

Don't know Ed.

But when I had the A/C diode fail, and the inductive spike of the A/C clutch engaging reset the EECIV, it was very obvious that the EECIV decided to go into limp mode and raise the idle. No CEL light illuminated. Pull off to the side of the road, restart the car and idle back to normal. It happened several times. But I think after the second time I realized it was coincidental with the clutch engagement and I immediately knew what was going on.
So I would turn off the EATC as soon as I started the car to avoid the problem until I could fix the diode.

But to be honest Ed, I've never seen the CEL light up on my dash, and I have pulled codes for failed ECT's, EGR etc...

Did the 88's have a CEL? Is my CEL burnt out? Is Ed's CEL burnt out?

If you guys haven't inspected/replaced your A/C diode as per the factory rework notice you are asking for trouble.
The factory recommendation is to clean the connections and test. I recommend replace and SOLDER in a new diode, otherwise the connections will just corrode again.

Not saying that is the de facto cause of high idle, just something you need to check.

Also keep in mind that the A/C can run in the winter. Defrost typically will turn on the A/C to dehumidify the air.

[DPDISXR4Ti]

'Splain why when the sudden high idle occurs the computer doesn't set the Check Engine light on the Scorpios.

No CEL on my '87 (USA early '88), so no first-hand experience. I think perhaps the logic to trigger a CEL needs to be more definitive - i.e. more failures and/or over a greater period of time. The whole idea of a CEL was new in the late 80's and so I could see them erring on the side of NOT triggering the idiot light unless there was a greater certainty that something was wrong. But this is all just speculation on my part.

[Ed Lijewski]

Yes, ^ speculation.

88's have the CEL.

On my 88 and 89 the CELs lit and remained lit after restarts due to defective ACT sensors.

On each car rarely and randomly the CEL might light during operation and stay dark on restart. I've not bothered to check for codes following those instances. As the FOMC might say, those were transient anomalies.

If I were Dean (thank you Lord...) I'd want to test the CEL bulb.

YMMV

[Ed Lijewski]

Also keep in mind that the A/C can run in the winter. Defrost typically will turn on the A/C to dehumidify the air.

Not surprising something re the A/C failed with it ready to engage so often.

I generally keep the AC off after summer ends and very occasionally switch it On during dry outside air conditions (November/December through March/April) unless the carpet got damp during rain or snow. I do actuate AC otherwise during those months just for a few minutes to circulate oil to keep seals lubricated.

YMMV

[brokencase]

Just an FYI

I was looking through EECIV Logic guide (circa 89') that I posted a while back.

On page 419 in the FAILURE MODE MANAGEMENT section there was a table that I thought was interesting (see below)

The way I read this table is as follows, for example, If ECT fails then the following happens...
Adaptive fuel - No learning
EGR is disabled
Thermactor Air is bypassed (does not apply to Scorpio)
Decel Fuel Shutoff disabled
Managed Fuel Air disabled (I presume this means O2 sensor compensation is turned off)
ECAD - Full Speed mode (does not apply to Scorpio)
EDF - Electical Fan Mode (don't think this applies to Scorpio)

What is interesting is the only failure that turns on "Idle Speed - Fixed duty cycle" for the Scorpio is failed Throttle position Sensor.
This is no surprise, it is a potentiometer and the wiper contact wears. I have replace more than one TPS. Moreover it fails
intermittently. So if you have sudden high idle then I would put a fresh TPS in, and don't swap in another old one.

I could not find anything (yet) regarding power loss or glitching as would happen for the failed A/C diode.
But it could be when this occurs erroneous sensor value are read across the board and the EECIV behaves as I have observed.
There is also a EECIV error code for power fail detection.

It is also worth mentioning that EGR system is turned off in the case of any sensor failure. That is important because you might be trying to figure out a problem and you may have determined that your EGR is not working, not realizing that the EECIV disabled it because some other sensor is bad.

Take this all a bit lightly as this document is circa 89. Strategies changed over the years. But it is in the ballpark timewise.

CEL started in the 88 model year. But I would suspect that some 88 Scorpios do not have CEL. I still need to check mine.
CEL will illuminate at startup for bulb check and turn off after the engine starts to turn over.

[DPDISXR4Ti]

What is interesting is the only failure that turns on "Idle Speed - Fixed duty cycle" for the Scorpio is failed Throttle position Sensor.
This is no surprise, it is a potentiometer and the wiper contact wears. I have replace more than one TPS. Moreover it fails
intermittently. So if you have sudden high idle then I would put a fresh TPS in, and don't swap in another old one.

Interesting info. Not terribly surprisingly (given the oddball nature of this issue), I've never gotten a TPS error code. I also have a relatively new TPS installed. That said, I could see where a power glitch might be seen as a TPS failure (among other things) and thus trigger the "Fixed duty cycle" (i.e. high idle) response.

CEL started in the 88 model year. But I would suspect that some 88 Scorpios do not have CEL.

I refer to my car as a 1987, as that's what it is everywhere but North America. The Merkur Scorpios built from Jan to July 1987 have lots of different "features" vs. the cars built from Aug 1987 onwards. The CEL was added starting with the Aug 1987 and later built cars. All North American Scorpios built from Jan 1987 to July 1988 get lumped in as "Model year 1988", and that has created issues. It's been a problem especially in California where the C.A.R.B. database indicates that all Scorpios are supposed to have a CEL, but the early cars clearly do not.

[Ed Lijewski]

On my '88 which experienced 3X sudden high idles I had installed a new Ford/Motorcraft TPS with the gold plated pigtail/harness connections. I made no notations of dates for any of the foregoing.

I'm certain I installed the new TPS not because of any idle issues but because the exiting TPS likely was original equipment and had 100K or more miles on it.

Yes, even new parts can develop glitches.

Data points.

The sudden high idle occurring on my '88 Scorpio would have RPMs race to and hold at ~2K+.

On one of my '88 XR4Tis the sudden high idle would rise and hold to ~1K/1.2/1.5K rpms. But never 2K+

I installed and set new TPS units on the XR4T but the sudden high idle issue recurred.

Both Scorpio and XR4Ti are EECIV managed. So why the differences between their high idle RPMs?

The Scorpio sudden high idle was scary as each occured in heavy traffic while slowing/stopping at a semaphore stoplight.

So, I doubt the sudden high idle is EECIV's controlled FMEM mode. More probable is the IAC somehow receiving 4.5v (causing it to open fully) via a cross-wire harness "short-circuit"; the ACT wiring on the Scorpio is bundled along with the IAC and TPS.

YMMV

[DPDISXR4Ti]

Took the Scorpio in for it's annual inspection this morning. About a mile out, I briefly had the car in neutral and noticed the idle was ~2200 RPM. I was on a straight downhill so I decided it was time for a rolling test... Shut the engine off and immediately re-started - idle calmed right down to ~1K and proceeded to destination and then home without event.

Thinking back on when I've had this issue occur, I think it has often (always?) been during warm-up. Once the engine is fully warmed up it does NOT go away - there needs to be a re-set.

Just adding another data-point.

[Ed Lijewski]

Additional sudden high idle data points: the 3X it occurred on my '88 the engine had been fully up to temperature for quite a while.

YMMV