Up & down idle 88 Duke when warm

[Donster]

I think I figured it out.  It's voltage to the ECU.  Either a bad power, or a bad ground.
Interesting how that worked out.

True statement Mike.
But after so many recommendations, I had to proceed systematically, especially not having a scanner.
Checking all the grounds would have been cheaper and faster, but in the beginning, the majority of recommendations suggested one of the sensors, so that is where I started my hunt.

Thnx!

\D

[GTRS Fiero]

I had happened to have been working on articles dealing with idle, the ECU, and grounds, at the time.  Since I've been continuing work on those articles now, I revisited that, because it again sounded like ground issues.  I thought surely that had been suggested, so I went back and looked.  Sure enough.

[Donster]

That pigtail ground is also very close to the ground that's on the outside of the frame rail.  It can be found by removing the right rear fenderwell liner.  It has been thought to be a major problem when the ground is poor. It's a black insulated wire so it probably comes out of a harness, unlike the braided grounds.

Could somebody please check the SM and let me know, exactly where this ground connection is?

Thanks.

\D

[Fierofool]

With the wheel well liner removed, it's attached to the outboard side of the upper frame rail, right about where it arches upward, or just a little behind it.  Once you expose the frame rail, it's very visible. 

I've done a search and have found pictures of rusted 87 and 88 frame rails but didn't see the ground wire.  I know I've seen pictures of the wire bolted to the upper frame rail.  I know you're getting some ground information from The Ogre.  Maybe he has a picture.  Or try Patrick.  He seems to have a good library.

[Donster]

No ground connection there.
Anyone know where it was supposed to come from? I'm assuming from the C500, inside the harness going to the passenger side rear lights?

\D

[Fierofool]

I saw Patrick's picture and that's on a Formula.  Other pictures I found of rusted 87 and 88 frame rails didn't show a ground in that location.  I'm wondering if it's located there only on the V6 and located elsewhere on the 4 cylinder because of the different harnesses. 

Just a suggestion for a solution.  While you have the fenderwell liner out, maybe install one there.  If they're available in Germany, secure one of those long post battery terminals, of the type that can be used to connect 2 batteries together.  Make your own heavy ground strap or purchase a good one and mount it to the frame rail.  The only unknown is from where the factory ground emanates.  What does it tie to the frame rail? 

[Donster]

From what I have heard today, the 88 Duke did not have a ground connection inside the passenger side rear fender well. Instead, that ground is under the center console, which is ALSO the ground for the fuel pump.

[Fierofool]

In that event, it may be allowing the fuel pump to fluctuate pressure. 

[TopNotch]

There's nothing wrong with adding grounds that are not documented.

[GTRS Fiero]

Hmmm.  I just got strongly criticized for suggesting that to someone.  They said to fix the problem, rather than add band-aids.

[TopNotch]

What if the problem is not enough grounds?

[GTRS Fiero]

Good question.  There were enough grounds from the factory, apparently.  Replacing a missing ground is fine.  If, however, a ground is no longer good, due to the frame rusting apart, for example, maybe the frame should be fixed.  My issue had to do with the wirinng mess left from the removal of an alarm system causing my gauges to be a bit erratic.  I'm tempted to pull the entire harness, and have the harness redone.

[Donster]

OK, finally got my diagnostic kit & cable.
Thought I had figured out TunerPro RT with the $48 definition file, but I don't trust myself and obviously, some of the readings don't make sense. I measured voltage with a DVM directly at the terminals and had 13.6 V!
Perhaps some of you can tell me what I am doing wrong.
Here is a screen-shot of the ALDL dash and the ALDL flags.



I also have the CSV file.

BTW-Idle is still hunting, matter of fact, getting worse..........thought I had it. 
HELP!

[TopNotch]

A low voltage reading at the ECM can be caused by leakage either on the supply side or the ground side. To check the supply side, measure with one meter lead on the battery + terminal, and the other on the 12V line into the ECM, with the car running. Any voltage you read at all is leakage somewhere -- possibly a bad connector somewhere. To check ground leakage, measure with one meter lead on the - battery terminal, and the other on the ECM case. Any reading here is ground leakage.
You'll probably need twp people to make these readings.

[Donster]

Thanks Pat.

Can somebody provide me with a wiring diagram, as I don't have a shop manual for the 88. 

Thanks.