Sudden Intermittent High Idle

[Ed Lijewski]

This points to something that hasn't been considered before.

Screenshot_20220201-175031_Lite.jpg (588.43 KiB) Viewed 4449 times

YMMV

[DPDISXR4Ti]

I don't see any smoking guns here Ed. The first comment about a factory service bulletin is lacking any real data at all. I'd classify it as hearsay unless something that looks more like evidence is provided.

As for the comment relating to the 2.8 EFI, that setup was only offered for one year, and only in Europe. Lots of changes occurred between the 2.8 and 2.9, including the intake manifold. Regardless, while an intake manifold gasket leak COULD be responsible for a high idle, it would likely be a more consistent condition.

[Ed Lijewski]

IIRC your two experiences of SSHI syndrome occured after you changed injectors twice. If you R&R-ed the intake manifold to do that, it would be worth considering taking a clean look at manifold, gaskets and bolts torque. I would do that.

Re the Granada bulletins, I thought Dean might use his internet search skills on it.

YMMV

[DPDISXR4Ti]

IIRC your two experiences of SSHI syndrome occured after you changed injectors twice.

Nope, I first experienced the high idle in March of 2019. Injectors weren't changed until 2020. I don't think I ever had the intake off any way.

[DPDISXR4Ti]

An interesting development occurred today while driving the Scorpio.... After a ~10 minute drive I pulled off the highway and was greeted with a red light at the end of the exit ramp. What did I find, but a ~3000 RPM idle. HOWEVER, without me doing anything (engine still running), after about 8 seconds the idle returned to normal and was fine for the rest of the trip.

So here's my working theory... The high-idle routine got triggered, but with the SD102 strategy ('89 ) it's only implemented for a short period of time before "normal" operations resume if the trigger condition doesn't remain.

[Ed Lijewski]

The incidents I experienced were on my '88 and appeared also only after slow down/stop for a red light with the engine fully warmed after several or more minutes of normal driving.

My thoughts on cause have been focused on the EGR system, i.e. the EGR solenoid sticking open, the EGR valve sticking open, or both, or even an errant harness signal causing the system to actuate when operating conditions don't call for that.

As an experiment you might disconnect the EGR vacuum hose to the valve, drive as you want, and see if the syndrome recurs or not.

YMMV

[DPDISXR4Ti]

My thoughts on cause have been focused on the EGR system, i.e. the EGR solenoid sticking open, the EGR valve sticking open, or both, or even an errant harness signal causing the system to actuate when operating conditions don't call for that.

I don't think the EGR valve sticking open would cause this condition. I'm reasonably certain that the Idle Air Control Valve is being commanded to open by the strategy. As proof, if you disconnect the IAC I bet you'd never experience the high idle. Note, you'd need to raise the idle to conduct this test, and probably keep your foot into the accelerator a bit at cold start.

But again, I think the strategy changed in 1989, probably because they realized this routine was getting triggered too often, and mostly it was unneeded.

[Ed Lijewski]

Note that I didn't suggest a stuck open EGR valve, but rather an issue where the solenoid might stick in open command mode.

How many problem free duty cycles are left in a 34 y/o EGR solenoid?

Why I've moved on from the IAC is that I've postulated it's totally illogical from an EEC-IV computer engineering concept to code a ~2500/3000 sudden RPM idle as the response in a limp home strategy. Why not just the typical cold idle rpm mode, ~1200 rpm +/- ?

That the syndrome most commonly appeared on slow down/stop also is more consistent with an uncommanded vacuum leak. The EGR pipe opening is very near if not equal to max IAC air flow.

Peeps are quick to replace IACs with new units for addressing idling issues. They/we should also consider replacing EGR solenoids with new units.

YMMV

[andyofcolumbusmerkur]

It would be easy enough to wire in an interior mounted toggle switch/relay to the IAC. That way you could test these thoughts without having to stop to disconnect the IAC.

[DPDISXR4Ti]

It would be easy enough to wire in an interior mounted toggle switch/relay to the IAC. That way you could test these thoughts without having to stop to disconnect the IAC.

True, but that seems like a bad idea for three reasons:

1) Cutting into the harness - especially for a circuit exposed to the elements - should always be a last resort.
2) You really only need to do this once to verify that it's the IAC that is creating the high idle.
3) The engine would most likely stall when you toggle the IAC fully off.

[DPDISXR4Ti]

That the syndrome most commonly appeared on slow down/stop also is more consistent with an uncommanded vacuum leak. The EGR pipe opening is very near if not equal to max IAC air flow.

Except that a leak of inert exhaust gases would have a very different effect from "fresh air".

[andyofcolumbusmerkur]

Well if you don't want to physically disable the IAC maybe there's a way to simply observe it while driving. Without going as far as running real time diagnostics aka data logging. Maybe modify a good tested spare IAC somehow, so you wouldn't do anything permanent to either the IAC or the cars wiring. Maybe do the EGR as well.

[brokencase]

Ed, I have a big collection of Merkur TSB's and I have never seen any regarding ESIHI.

There was one re-work that not all early cars may have had done and that was where they drilled out the hole in the throttle plate and swapped in a new ECCIV. The revised EECIV part number that was installed was E8RY-12A650-YA

This was part of the massive "M57" update that dealers did to address multiple TSB issues

"ISSUE: A rolling idle or surging condition may be
caused by an imbalanced airflow
between the cylinder banks and the
strategy of the EEC IV processor.
ACTION: To correct this, modify the diameter of
the air bleed hole in the throttle plate,
reset the idle speed and install a new
level EEC IV processor. Refer to the
following service procedure.

I'll bet most of the early cars had this change performed.

Another issue that was addressed during the M57 rework was the bad connections to A/C clutch "back EMF" diode.
The TSB only had the techs clean the connection to the diode. The permanent solution is to SOLDER the connections to the diode. If any of you have not done this then I suggest you do so. Given the car's age I suggest soldering in a NEW diode.

I had mine fail and the car's idle did suddenly jump up until I pulled the car to the side of the road and shut it off and re-started it (as well as turning off the A/C)

This is the only instance of sudden high idle I have ever experienced.

[DPDISXR4Ti]

Lots of good info in the above ^^^ post. A couple comments/questions...

- The E8RY.... part# indicates a North American service part for a Merkur. I've never seen this one - I wonder what the strategy number is? EFI-SD102 perhaps?

- Is the size of the over-bore of the hole in the throttle plate indicated?

- You may note earlier that I have the A/C diode on my list of things to test. If it tests okay I'd probably just refresh the contacts and then coat with Kopr-Shield. Some guy told me it's pretty good stuff.

[Ed Lijewski]

Ed, I have a big collection of Merkur TSB's and I have never seen any regarding ESIHI.

It's SSHIS.

It's not covered in your collection cuz it appeared, Suddenly, later on in (some but not all of) these cars' lives.

YMMV