IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

General discussion relating to club happenings and items related to Merkurs in general such as "Merkur sightings". If you just signed on, please feel to start a new thread and introduce yourself here. Posts specifically regarding either the XR4Ti or Scorpio should go in those specific forums. Feel free to make suggestions on improving this forum here as well.
Ed Lijewski
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Ed Lijewski » Tue Sep 25, 2018 12:44 pm

After three weeks of daily driving haven't had any sudden/high idle episodes. Idle currently is good in all situations.

The change of TPS unit made the difference.

YMMV
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Lijewski: "Sum Ergo Drive-O. Mucho!

my8950
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by my8950 » Tue Dec 04, 2018 12:57 pm

Interesting read....

dimswits
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by dimswits » Tue Dec 04, 2018 4:46 pm

Some years ago I inadvertently stumbled on the root cause of this while datalogging my turbo scorpio. I didn't have a bad TPS, rather, it was faulty wiring power distribution wiring, but the symptoms are exactly the same: The car drives fine for a while, then as if by magic, when coming to a stop during the drive, the idle revs up to 1500 rpm or so, and stays there. Cycling the car off and on fixes the issue for a short time, but it always returns.

The EEC-IV registers closed throttle as the lowest voltage reported by the TPS that is also greater than 0.49 V. Part throttle is a variable value that is 0.04 V higher than the closed throttle value. The closed throttle value is a continuous ratchet, meaning it's always the lowest value seen by the EEC for the current driving session.

What I was seeing in the datalog is my TPS would be at .85v closed. I'd drive and warm up the car. On decelerating to a stop the engine RPM would dip momentarily, causing an overall voltage drop in the whole car, and the TPS would correspondingly report just over 0.55v. Just for an instant. That 0.55v becomes the new closed throttle, and the normal closed TPS setting of 0.85 is 6 times the difference needed to trigger part throttle. Since the closed throttle voltage cannot increase, the car can never drop from part throttle mode down to closed throttle, and so the timing stays advanced and the IAC stays open.
Dimitri in NYC
88 Scorpio 2.5 Turbo
89 Scorpio 4.6 DOHC
02 E46 330Ci
17 MKC

Ed Lijewski
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Ed Lijewski » Tue Dec 04, 2018 6:17 pm

That seems to suggest an EEC failure of dashpot mode, which shouldn't occur, but randomly does. But why?

YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!

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Bob Weir
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Bob Weir » Fri Dec 07, 2018 1:53 am

Hi Ed

You already have Dimitri, but maybe you can contact Ken Kizer [http://www.aphenos.net/scorpio.htm] and Darren Needham for help. I have phone & email if needed.

my8950
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by my8950 » Fri Dec 07, 2018 9:37 am

Bob Weir wrote:
Fri Dec 07, 2018 1:53 am
Hi Ed

You already have Dimitri, but maybe you can contact Ken Kizer [http://www.aphenos.net/scorpio.htm] and Darren Needham for help. I have phone & email if needed.
The is 404'd....

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