Bad / Hunting idle 88 Duke when warm / hot (Page 3/8)
Patrick MAR 28, 03:34 PM

quote
Originally posted by Donster:

Stalls / dies.........instantly.



Hmmm... I'm surprised. I had an idle hunting problem with a '94 Hyundai Elantra, and my solution (although inelegant) was to simply unplug the IAC while the engine was running (and at the low end of the hunting idle RPM range). Solved the problem. No trouble codes generated... and the engine continued to start, run and idle just fine. It's too bad a procedure this simple apparently won't work with an '88 duke.

[This message has been edited by Patrick (edited 03-28-2019).]

Donster MAR 30, 08:59 AM
Rebuilt TBI with new gaskets, O-rings and everything else, still hunting idle.
The only thing I have not yet replaced are the 2 ignition coils.
Could they be at fault??
Donster APR 01, 01:05 AM
So, does anybody think it could be the coils?
I've replaced so much, it really wouldn't matter to me if I need to replace the 2 coils, I just want to know if they could be the problem before I replace them, as it is rather difficult to get to them.
theogre APR 01, 05:40 PM
Ignition is Not likely for this problem.
See my Cave, DIS Ignition

You didn't scan the ECM all this time?
Should done this First.
Example: ECM reads Volts etc to ECM and will cause problems when ECM sees low or high volts often not setting "Codes." Crap wiring in a lot places can cause this problem even tho Alt putouts ~14.6 volts.
ECM can be "dying" or any wires to it can be crap.
Some sensors should read relatively constant while others charge every scan.
See my Cave, Scan Tool Help and rest of section.
reddevil has scan tool works w/ 87-88 duke.
Donster APR 02, 01:22 AM
Perhaps you can point me in the direction of possible bad wires/ground? Or are there too many?
I've taken apart the C500 next to the battery and redone all of the wires.
Wich are the ground wires that could have such an effect on the idle?

I ordered a scan and diagnostic kit for the 87-88 Duke yesterday, what exactly, when I scan, should I look for?

As always, your input and suggestions are much appreciated!

Thnx

\D
theogre APR 02, 03:23 PM
ECM read cave section.
Example: ECM should see and post to scan tool same or very close to same Volts as Volts measured at battery AND alt output terminal and red wire to alt's side plug.
IOW Alt should be ~ 14.6v when running then ECM should see and report ~ same.
If ECM see < than that like under 13.6v or worse 12v then have a major wiring problem(s) causing low volt.
Worse, Same problem is likely cause low volts to a lot of other things including fan motor, heat blower, etc, covered in Electric Motors that can kill them too.

Even if they match... Start check/clean/fix all grounds listed in cave. Take all apart not just look at the ends.
If rusty or painted clean to bare metal and coat the metal w/ brake/silicone grease. Don't over tighten and break things because grease make that easy.

Then do same for battery cables and alt output wires etc.
Better to just replace battery cables w/ ACDelco parts, not aftermarket cables w/ lead battery ends. Coat w/ brake/silicone grease. Use small 5/16" wrench and tighten just enough to deform the lead on battery and hold. Doesn't need much to "strip" the battery nuts inside the holes. Many fools wreck the battery using bigger wrenches. Big reason Why many sell "battery wrenches" just for this job.

Another example: If alt's mounting hardware is iffy... The hardware IS ground for the Alt. Crap hardware = Crap ground and often can see measure volts output to case then output to engine. Common to loose 1v or more just for crappy alt hardware. Then when you have other iffy ground and/or + side you can drop 2 or move Volts to any or all of car.
What More Fun? Try turning on HeadLights w/ engine running. Measure Volts alt output to case then output to frame then in front @ HL socket black wire to whatever wire is have power. (Leave socket on the bulb to measure. you need both bulbs amps load to see this better.)
I bet HL is 1 - 4v or more lower then back because likely have crap grounds in front and problems w/ HL main and/or dimmer Switches at minimum. 1v drop often won't matter and won't see dim light but higher V drop then likely will see dim lights and heat up the dimmer and/or main switches because they wear out and get more resistance.
Donster APR 05, 04:18 PM
Scanner / diagnostic kit has not arrived yet, but...........today I had the exhaust out to repair it (long story) and I noticed that from underneath, you can see a bracket from the alternator to the TBI. It was completely rusted and once I looked at it closer, I noticed the screw going into the TBI is torn off, hence, no real connection there. I remember the Ogre mentioning that the bracket itself functions as ground. Is it this one??
Could this be my issue??
Donster APR 07, 08:35 AM
Tore apart center console today, checked all ECM cables there, sanded down ground connector, used a stainless steel screw.
Went at the C500 connector again, replaced positive cable from battery to underneath C500 block, replaced negative cable to engine, replaced ground cable from engine to chassis, sanded all surfaces.
No change, idle still hunting. Scanner / diagnostic kit won't arrive until sometime next week. Had fun troubleshooting in the beginning, sort of a challenge. Now frustration is setting in.

[This message has been edited by Donster (edited 04-07-2019).]

theogre APR 07, 10:51 AM
Alt "Ground" is all mounting hardware to Alt case. If you have crap/damage/missing hardware then fix/clean all.

87-88 Alt uses 3 brackets...
top is belt tension case
bottom is bracket to block
back is bent/stamped rod to intake man

All should be there or tension part might break the hole because is some what weak.
Donster APR 08, 05:30 AM
Put in a RD belt tensioner 2 months ago.....
All alt grounds replaced.......but........
Quick question regarding the ground connections:
I have a heavy gauge wire that goes from the (-) battery to the engine block (good shape).
Then I have one that goes from the engine to the decklid frame (flat copper, good shape).
But shouldn't there also be one directly from the (-) battery to the body/frame??
Is it vital?
I don't have that. Where would/should it be connected to the frame?