Bad / Hunting idle 88 Duke when warm / hot (Page 4/8)
fierofool APR 08, 08:05 AM
On the V6, the alternate ground comes off the negative terminal and bolts to the battery tray. Maybe the L4 is the same.
Donster APR 09, 01:22 AM

quote
Originally posted by fierofool:

On the V6, the alternate ground comes off the negative terminal and bolts to the battery tray. Maybe the L4 is the same.



Thanks Charlie. I think they are the same. Been looking thru the forum and I kept reading about the direct ground from (-) battery to the tray/frame/body, and it seems to be V6 AND L4.
Would be great if I had an 88 SM to flip thru. :-)

[This message has been edited by Donster (edited 04-09-2019).]

armos APR 12, 11:20 AM
Did you inherit this problem from the previous owner, or did it start doing this later on?
How warm does it have to get before it starts idling badly?

You mentioned replacing the injector, but have you checked if it's actually spraying okay and there's no dripping? Are you sure it's the right injector for the car?
I've read you can use a timing light to see the spray pattern as it idles (never tried it myself). Warm idle is when the injector is operating at it's minimum duty cycle and that's when they're most prone to be erratic. It's also when they're the hardest for the ECM to accurately control.
Warm idle is also sensitive to sensor/wiring issues for basically the same reason. Definitely review all the sensor data when you get your scanner.

Make sure the air passages for the IAC are clean.
Donster APR 12, 04:26 PM
Unfortunately, the issues were inherited.
Injectors were both tested by Bosch Services. I had no idea that they do that here in Germany. Tested out good.
I also have good fuel pressure.
Donster APR 14, 08:14 AM
OK, the more ground / earth connections I replace or clean up (stainless steel bolts & nuts, grind to bare metal), the better the car runs.
Seems almost perfect now, except for a slight stutter/drop in the idle every now and then.
I'm still waiting on the scanner, but I am obviously on the right track here.

As usual, I will update here every time I do something.
theogre APR 14, 12:05 PM
You adding SS hardware may not be helpful in the long run. Adding more different metals can make worse problems when polluted water get on whatever. Worse if you don't use silicone/brake grease to keep water off the metals. Even in the cabin you get enough water as condensate as wet air hits anything cool.
Just google: dissimilar metal corrosion
Donster APR 16, 02:43 AM
Ogre,
I DID heed your advice and used silicone / brake grease on all connections that I cleaned / replaced.
The stainless steel was more for troubleshooting than anything else, as you have better connections / conductivity when first used. In essence, I was just trying to find which ones would have the most impact. They can all be replaced again eventually, with regular bolts and screws.

And I'll say it again: Your insight and recommendations were vital in hunting down the hunting idle (no pun intended).
I'll update once I receive my scanner or have any changes / improvements.

THANK YOU!!
theogre APR 16, 11:25 AM
Grease should protect w/o tearing SS out then.

Hunting idle isn't only thing fixing ground will help.
Like front grounds near HL assem's effects most things in the front of car but will never set ECM codes, hunting idle, etc.

Note that you often Won't see iffy grounds and connectors w/ most Ω meters. Even 20awg wire and related connections are too heavy to see a difference using them.
Often can see brighter HL bulbs by cleaning front ground and bulb sockets. Other bulbs might not see a diff unless grounds etc are really rotten.
Rest often can see problem testing for voltage drop on a wire, more so w/ big amp loads say rad fan but easier just fix/clean all grounds.

Work thru ground etc in engine bay and two main ground in the cabin.
While sounds weird... the Fuel pump is grounded in the cabin.

Can try removing/replacing some plugs too even if they are "water proof."
Alt side plug, ECM, large one next to ECM, C500, and "Box" w/ bolts under C500 for a start.
Sound dumb but Replugging connectors a couple times often cleans minor corrosion and fixes a lot of issues.
This ECM more so because board edge connections sim to PCI etc in a computer but just plug connecting to solder on board edge. IOW Plugs works same as PCI but ECM doesn't have "gold fingers" like PCI does and solder will corrode over time alone.
Do Not disassemble the ECM beyond cover over PROM. This can cause problem just removing main cover because is bolted to part on the board and old ECM can "die" w/o warning.
Donster APR 17, 05:01 AM
I'm going to write a book with all the tips you have given me! :-)

BTW: I was told on the GA Fiero forum, that there is a ground connection in the rear right fender well that is notorious for causing issues / bad ground.
Where exactly is it located?

Thanks,

\D
olejoedad APR 17, 07:39 AM
Remove the right rear wheel well liner.
It's located on the outboard side of the upper frame rail at about 11 o'clock.
It is a clip that's bolted to the frame rail with a heavy black wire.