Up & down idle 88 Duke when warm

[GTRS Fiero]

Did you replace the screw to the TBI?

[Donster]

Did you replace the screw to the TBI?

The only way to do that would be to take out the entire TBI, put it on a bench and drill out the torn off screw, then cut new threads.
Instead, I got another angle-iron and fastened it to a hole with threads in the TBI right next to the torn off screw and to the alternator.
Unfortunately, it didn't seem to be the cause of my idle issue. 

[Donster]

.......and another 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 (good shape).
But shouldn't there also be one directly from the (-) battery to the body/frame??
I don't have that. Where would/should it be connected to the frame?

[Fierofool]

The V6 Negative cable has a secondary ground wire that attaches to the battery tray, down toward the shock tower.  Maybe the L4 has the same setup.  I have a new ground cable that I think is for the Duke, and it has the same ground wire as a V6 cable. 

[TopNotch]

But shouldn't there also be one directly from the (-) battery to the body/frame??
I don't have that. Where would/should it be connected to the frame?

You should definitely run a ground from the battery negative to the body. Who knows, it might even fix your idle problem.

[Donster]

The V6 Negative cable has a secondary ground wire that attaches to the battery tray, down toward the shock tower.  Maybe the L4 has the same setup.  I have a new ground cable that I think is for the Duke, and it has the same ground wire as a V6 cable. 

Replied on PFF........thnx

[GTRS Fiero]

Interesting.  Several posts on the fuel pump, the OPS, and fuel pressure, but I don't see that the pump was replaced.

[Donster]

new pump in 2017, recently checked fuel pressure, all good.

[Donster]

OK, the more ground / earth connections I replace or clean up (stainless steel bolts & nuts, grind to bare metal, new weaved copper or stainless steel ground cables), 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.
\D

[GTRS Fiero]

I did an article on sensors and locations for the V6, since that is what I have, but maybe should do one for the L4.  Much more difficult, though.

It would certainly help those unfortunate L4 owners. 
\D

I have to rely on people with an L4 to provide pictures/info.

[GTRS Fiero]

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.

[GTRS Fiero]

This is for the V6, but should be similar.

Have you ever checked their ECM supply voltage to see if it is changing?  Some people have reported that adding ground wires have help their idle.

In the ECM prom there is actually a section that controls idle speed depending on battery supply voltage.
If the voltage dropps to 8 volts, the idle speed would be adjusted to 1200 rpm.  At 14.4v it drops back to 900 rpm.


Here is a table:

Volts Idle
8.0 1000
9.6 1000
11.2 900
12.8 900
14.4 900

If the power to the ECM changes you could get into an loop where voltage drops, idle is increased, voltage comes up, idle is decreased. Sound familiar?

Try a battery charger to see what happens.  Maybe have the voltage regulator in the alternator tested.

Maybe feed a stable 12V to the ECM.
Put a Volt meter on the power to the ECM.

The question was sortof answered.

[Raydar]

OK, the more ground / earth connections I replace or clean up (stainless steel bolts & nuts, grind to bare metal, new weaved copper or stainless steel ground cables), 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.
\D

Interesting...
Now that you mention this, I seem to remember the "hunting idle" issue associated with using the disk-type injectors with the V6 Fiero ECM (3.4 swaps being the major culprit), being blamed on voltage fluctuations.

You might be on to something.

BTW... In every Fiero I've ever seen, there was a lighter weight pigtail coming off of the negative battery terminal, that is screwed into the frame, near the passenger side shock tower.
Since you have a large ground going from the battery to the block, and a strap going from the block to the hinge box on the frame, I wouldn't have thought this would be an issue, but stranger things have happened.

Edit - 87s and 88s have a built in stutter to the idle. Almost sounds like a random skip, several times a minute. It's quite normal (and has been commented on, before, elsewhere.)

[Fierofool]

Edit - 87s and 88s have a built in stutter to the idle. Almost sounds like a random skip, several times a minute. It's quite normal (and has been commented on, before, elsewhere.)

That's interesting.  My 87 does it.  I don't recall noticing it until the 3.4 swap.  I always assumed it was one of the injectors causing what sounds like a slight miss at idle.  Of course, that wouldn't be the case in the Duke, having just 1 injector. 

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. 

[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. 

That will be the next thing I check. Might as well, as I have done just about and replaced everything else. 

I'll update any changes, improvements.

\D