Up & down idle 88 Duke when warm

[Donster]

Unplugging the MAT sensor also did no good?

Also no change.

[GTRS Fiero]

Hmmm.  So it is apparently not a sensor.  It could be the ECM itself, a wiring issue, or...?

Hmmm.  What happens if you remove the thermostat?

[GTRS Fiero]

After thinking about this, have you run WinALDL on this?  I don't know if it works on the '88 Duke or not, but you need to know what values the ECU is reading.

[GTRS Fiero]

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

[Donster]

Question: Could an incorrectly wired Oil Pressure Sensor have an influence on the idle?

Anybody?

After thinking about this, have you run WinALDL on this?  I don't know if it works on the '88 Duke or not, but you need to know what values the ECU is reading.

Can't do WinALDL on an 87 or 88 Duke, software is not compatible.

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

Can you elaborate?
Thnx,
\D

[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.

[GTRS Fiero]

For the oil pressure sender wiring being the cause, just unplug the sender.  The wiring would have to have shorts or run to the wrong things to cause such an issue.

[Donster]

It is obviously NOT the OPS (All 3 wires now connected). Found some ground connections that look as if they could be flaky. But it was so freaking cold in the underground garage today, further work will just have to wake until it is a bit warmer.
\D

[Donster]

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

I don't think this would be temperature dependent. True?

\D

[Donster]

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

Well, I need pictures.

Let me know what to take pictures of, and I can provide.

\D

[GTRS Fiero]

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

I don't think this would be temperature dependent. True?

\D

Well, everything runs OK on pre-set values.  The issue obviously occurs after the ECU starts running things off of the sensors.  Since the sensors aren't the issue, the issue is somewhere with the ECU itself.  Unless the ECU is bad, the issue is voltage.  The ECU does not start running off the sensors until the engine has warmed up, so yes, something with the engine being warm.

Since voltage has a dramatic effect on the ECU, that is a highly likely source of the issue.

In theory, when you unplugged the CTS, resistance should have gone to infinite, as in cold.  Unless there is a short somewhere.

Keep in mind that the L4 is foreign to me.

[GTRS Fiero]

Let me know what to take pictures of, and I can provide.

\D

I sent you an email.  I can't do more than start on this, for now.  I have some content, but the L4 is much more difficult than the V6, because there are 3 different versions of the L4: 84, 85-86, and 87-88.  I am not enough of an expert to know all the differences.  Basically, I don't know what I don't know.

If you can help with this, that would be great.  I'm trying to show how things should be, so only stock, where possible.  I'm afraid that probably 90% of the pictures in the newsletters are my Fiero, or parts at the house.  Since my Fiero is no longer stock, getting pictures is difficult.

[Donster]

Got your list, thanks.You will need to give me a few days, as it is constantly between 28 - 30 °F here and makes doing anything on the car no fun.
\D

[GTRS Fiero]

No worries.

[Fierofool]

I sent David Brill an email earlier in the week asking what happened to The Phoenix and Purple Haze and haven't gotten a response, yet.