Up & down idle 88 Duke when warm

[Donster]

Part arrived within 4 day. Not bad from US to Germany. No additional customs/duties. Only problem is.....it did not resolve the idle issue.
So here is what has been done:
All vacuum lines checked
New plugs
AGR valve blocked
New MAP sensor
New IAC valve
New TPS
New Throttle Body Housing gasket (today)
New TB injector (today, identical)
..........now I'll replace the ignition cables (Monday)....then I have checked or replaced just about everything I can think of.

[GTRS Fiero]

"AGR valve"?

I don't know about the TB injector.

Have you replaced the CTS or MAT sensors?  If it runs OK when cold, but has issues when warm, that means that the preset values are fine, but the problem is sensor input.  The master sensor is the CTS sensor.  The CTS and MAT sensors work as a pair.  I don't know if you could test the CTS by unplugging it or shorting it.  Basically, make the ECU think that the engine is cold.

The ignition cables should not be the issue, because they do not go bad when the engine gets warm.

[Donster]

MAT or MAP sensor?

[GTRS Fiero]

MAT = Manifold Air Temperature

Also called IAT = Intake Air Temperature

If this fixes the problem, I'd like a pic of the sensor installed.

The MAP = Manifold Air Pressure sensor probably isn't the problem, although it is a possibility.

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.

[Donster]

"AGR valve"?

Got German and English mixed up there. ARG = Abgas-Rücklauf-Ventil, in English that would be Exhaust Gas Recirculation Valve, so AGR=EGR :-)


\D

[Raydar]

  I don't know if you could test the CTS by unplugging it or shorting it.  Basically, make the ECU think that the engine is cold.
...

Unplugging a sensor will (of course) set the code for that particular sensor.
If I understand correctly, it will also cause a pre-programmed "nominal" value to be plugged in to the operating program. Something that may not be optimal, but will allow the engine to at least run safely, and not damage itself. It will also make a "best guess" as to what it should be doing, based upon input from the other sensors.

[GTRS Fiero]

So, unplugging the CTS would force the ECU to continue running on pre-set values.  If the problem persists, the issue is likely not the CTS.  Inexpensive, easy, and effective.

You can also test with a multimeter, with key on after the engine is hot.

[Donster]

OK, CTS replaced, no change in symptoms, idle is still hunting (up/down) when hot.Next, as soon as they arrive, I'll replace all spark plug cables. Then the only thing left, based on the recommendations here, is the MAT.
Question: Could an incorrectly wired Oil Pressure Sensor have an influence on the idle?
Thnx.
\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

[Donster]

Unplugging a sensor will (of course) set the code for that particular sensor.

BTW: I unplugged the CTS while the engine was running, but it did not throw a code. Should I unplug it when the engine is still off and then run the motor for a while?

\D

[Fierofool]

The CTS circuit seems a little odd to me.  It probably doesn't matter if the engine is running or not when it's unplugged.  I have never seen a failed CTS set a trouble code.  It really doesn't know what the temperature is.  Just that it's sending info to the ECM to control the fuel/air ratio based on what it thinks the engine temp is.  It has nothing to compare to.  It might cause an O-2 code to come up.  My 87 CTS failed while sitting at the traffic light at Ga. 316 and Ga. 20.  Just suddenly was trying to die and clouds of black smoke coming out. 

I got to a shop here in town and a scan showed the CTS was reading 28*f and there had been no trouble code set.  I unplugged it and drove down to the parts store and got a new CTS.  Only during the drive did the light come on and set a code. 

[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

Well, I need pictures.

[GTRS Fiero]

Unplugging a sensor will (of course) set the code for that particular sensor.

BTW: I unplugged the CTS while the engine was running, but it did not throw a code. Should I unplug it when the engine is still off and then run the motor for a while?

\D

Did unplugging the CTS make any difference in the idle?

[Donster]

Did unplugging the CTS make any difference in the idle?

None.

[GTRS Fiero]

Unplugging the MAT sensor also did no good?