Sudden Intermittent High Idle

[DPDISXR4Ti]

He wrapped some insulating tape around wire connectors coming out of Air Bypass Valve. Each time the RPM's would go up, I simply opened the hood and gave them a squeeze using my fingers. That's all and the engine reverted back to normal on idle.

This sounds like a harness problem and by squeezing the wires you were re-setting the IAC. You could have done the same thing by disconnecting and reconnecting the quick-connector.

[DPDISXR4Ti]

deteriorating capacitors in an "EEC" sounds reasonable.

There's no question that failing capacitors are a problem with the Ford PCM's of this era. Some are more prone to failure than others - early 90's F-150 PCM's are almost always failing. In general, our computers seem to be holding up a little better, but that doesn't mean they're exempt from this problem.

My experience with this issue leads me to mostly agree with Dean... The strategy is commanding the high-idle as a fail-safe reaction to some sort of error. However, what I believe to be the case is that the strategy is needlessly kicking in too readily, with just the smallest, shortest of errors. I'm optimistically thinking they may have "fixed" this issue with the 1989 Scorpio PCM, much the same as I've witnessed with early 90's 2.3 PCM's NOT displaying the high idle response.

[brokencase]

You must have an intermittent harness/connector issue if the codes 21 and 24 appeared and then went away.
It is of no surprise that the EECIV raises the idle if abruptly it no longer knows what the temperature is.
It also comes as no surprise that this happen in the cold temperatures. Things contract when they are cold. So a marginal connector might not make good contact when it is cold.

When you shut the engine off and then restarted it the intermittent was gone.

Limp mode is not a single state, it is a series of distinct strategies employed to workaround individual sensors that have failed (or connections to them failed). One such strategy the EECIV code might do is to use the ECT temp value if the ACT had failed (or vis versa). Another would be to use rpm, throttle position, and math to estimate the manifold pressure if the MAP sensor failed. The idle may or may not be raised in the various cases of "limp home modes"

And...what, pray tell, is code 52 on the Scorpio?

Lets make it a rule that if you post eeciv error codes on the forum you have to post the descriptions (or at very least what you think they are).

[Ed Lijewski]

I just don't believe the SSHI syndrome () is limp home mode/strategy. Elsewhere I suggested several reasons why the excessive high idle mode is illogical, from the view point of ground-truthed computer engineers and most importantly vehicle operators.

Another reason is that in my experience nor in anyone else's who has written about it (to my knowledge) has limp home mode ever/EVER illuminated the Check Engine Light.

Ergo, the ECU didn't detect a sensor fault, yet the high idle resulted.

That uh doesn't compute.

YMMV

[andyofcolumbusmerkur]

I think we are calling it limp mode, but it is totally different than say a 2005 BMW that goes into limp mode. In which the car will not rev beyond a certain rpm, it may not shift into higher gears or reach highway speeds, plenty of dash lights glowing etc. I like the "get you home at all costs" engineering strategy that the Ford engineers used. Seems totally opposite to the thinking of more modern cars.

[Bob Weir]

"limp mode" same thing in my 94 Benz e320 Wagon. It would run, but only at slow speed. It had self destructing wire insulation in the throttle body. I was lucky and found a small shop in FL that only charged $500 compared to the VA firm that wanted ≈ $1500.

[DPDISXR4Ti]

You must have an intermittent harness/connector issue if the codes 21 and 24 appeared and then went away.

That's been my assumption as well. And since they always return together, it seems much more likely to be a shared GND or PWR circuit. Keep in mind, they "went away" after I changed PCM's, so clearly a power re-set occurred when I did that.
My wife drove the car about 100 miles on Thursday with a 8-hour park and cold start in 15 degree temps. No high-idle issues. However, I pulled codes today and 21 & 24 reappeared. I've cleared them. Let's see how long it takes for their return this time.

Limp mode is not a single state, it is a series of distinct strategies employed to workaround individual sensors that have failed

Agreed. Maybe we shouldn't even be calling it "limp mode" as that implies a "barely able to make it home" sort of state. I was just surprised to see that it never went out of closed-loop operation during the high idle mode.

And...what, pray tell, is code 52 on the Scorpio?
Lets make it a rule that if you post eeciv error codes on the forum you have to post the descriptions

Agreed, that's why I posted this on the first page of this thread.
"52 Power Steering Pressure Switch/circuit open"

[brokencase]

Sorry I didn't recall the earlier mention of code 52.

Problem is Scorpios don't have a power steering pressure switch...Right?

Are you sure it is a code 52?

Either the code was a miss-read or the EECIV is from a vehicle that has a power steering pressure switch.

[Ed Lijewski]

Yeah ^.

Possible code reading mistake for 51, or 53?

Screenshot_20220130-183811_Chrome.jpg (68.4 KiB) Viewed 4867 times

YMMV

[DPDISXR4Ti]

Are you sure it is a code 52?

Definitely 52. The car got exercised yesterday for a relatively short trip - 15 minutes in each direction but with an ~8 hour sit in 20 degree temps. No high idle and I just now pulled the usual codes - 21, 24, & 52.

I agree that the code 52 is a bit of a mystery. Just re-checked the schematic and indeed there is no P/S pressure switch indicated. The 8GHB and 8GHC are the only PCM's I have had in the car under my ownership.

Regardless of whether or not 21 & 24 are responsible for the high idle, I want to address that issue. Looking at the schematic, I need to tear into the harness and inspect splice S111, which is shared across a bunch of devices. Then I need to check Connectors C1935 and C1936, which seems to be located behind the instrument cluster, if I'm reading things correctly. Lastly, I need to check the proper operation of diodes WOT Cutoff Relay Diode and Throttle Air Bypass Valve Solenoid Diode.

[brokencase]

That harness to ECT and ACT are in a hot area under the manifold. I would bet this area is where your problem resides.

I would also apply a small dab of Kopr-Shield grease to the associated connector prongs at the sensors.
It goes without saying that I have already done this.

Is this EECIV module original or some kind of aftermarket unit? The code 52 would seem to indicate it is from some other Ford vehicle.

[brokencase]

Perhaps EECIV is from an 88 or 89 Ranger, which did have a power steering pressure switch?

Maybe somebody fooled you by swapping the label? Cheapo aftermarket unit?

[DPDISXR4Ti]

Perhaps EECIV is from an 88 or 89 Ranger, which did have a power steering pressure switch?

Maybe somebody fooled you by swapping the label? Cheapo aftermarket unit?

Both the 8GHB and 8GHC are Merkur Scorpio only PCM's. Both are factory original - I've been inside both of them and the ID on the EPROM confirms their originality. While I'm not really concerned, it is odd that nobody else has reported this. I think I'll start it as a new thread though, as I'm pretty certain it is unrelated to the high idle "issue".

[DPDISXR4Ti]

That harness to ECT and ACT are in a hot area under the manifold. I would bet this area is where your problem resides.

Myself and others have experienced issues with the similar shared GND circuit on the XR (it's just a big ugly splice within the harness). It's even more typically an issue with that car as the splice is right in the neighborhood with the battery which is so nicely heated by the turbo.

I know I won't get to this until Spring, and there's a benefit to that. At this point I've swapped in the '89 PCM and while the 21/24 errors have continued to return, the high idle has not. This would support Ed's suggestion that the high idle issue was "fixed" for the '89 cars. "Fixed" is probably too strong a word though; I suspect whatever is commanding the high idle on the '87/8 strategy (SD100 & SD101) was changed for '89 with the SD102 strategy, and no longer is a high idle commanded for whatever series of events triggers it on the SD100/101 strategy.

[Ed Lijewski]

Screenshot_20220201-132940_Lite.jpg (403.29 KiB) Viewed 4847 times

...

Screenshot_20220201-132919_Lite.jpg (332.13 KiB) Viewed 4847 times

YMMV