Up & down idle 88 Duke when warm

[Fierofool]

I don't know which is the primary path for power to the fuel pump.  The FP relay or the OPS.  I do know that if the oil pressure drops below a certain point, it should shut down the fuel pump, so maybe that's the primary path.  Since the relay shuts off after prime, that would leave the OPS as the primary voltage source for the FP. 

Look on the side just below the fuel pressure regulator and just to the left side of the IAC to see if the cap for the idle stop screw has been removed.  It may be that it's been tampered with since you're finding so many other things the OP 'tweaked'. 

[Donster]

Hey Charlie,
I've read about the idle stop screw, but I doubt that messing with it could cause my problems just like messing with it could also not eliminate my problems. I have read that screwing around with that screw can actually make things worse, hence the factory seal to prevent knuckle-heads like me from messing with it. 
I just have a hunch that there has probably always been an issue with the OPS and the PO couldn't figure it out so he, as you put it, "tweaked" the wiring and thereby messed things up even more. And why put in an 87 OPS, if you have an 88 OPS lying around?? Just a guess, but I'm starting to get desperate now.
\D

[Fierofool]

The thing about the two oil pressure sensors is that they have identical electrical circuits, just different connectors. 

[GTRS Fiero]

Somehow, I thought this was an L4.  Excuse my ignorance, but does the L4 have an idle adjustment screw?

[TopNotch]

The purpose of the idle adjustment screw is to maintain a slow idle should the idle air control not open. It is supposed to be adjusted to 600 RPM with the idle air control closed.

[Fierofool]

Somehow, I thought this was an L4.  Excuse my ignorance, but does the L4 have an idle adjustment screw?

They do.  It's used to set the opening of the throttle body butterfly valve on both L4 and V6.  A wire-type feeler gauge is inserted into the space between the lip of the butterfly valve and the side of the throttle body to set clearance. 

The adjustment screw isn't a metering needle, but a detent against the butterfly.  Like the old throttle set screws on carbureted engines. 

[GTRS Fiero]

I have been doing research on the harmonic balancer.  Supposedly, it can affect idle.  That is as far as I have gotten.  I know the '88 has one, but not if it is used for timing.  I have no idea how it could/would affect idle.

I also know that voltage can affect idle.  I have not gotten far in my research.

Here is a thought: the 2nd IAC seemed to fix things, for a bit.  Is it possible that the problem is the IAC, but something happens to the IAC, and then the symptoms return?  That would indicate either a wiring issue, or a lot of buildup causing the IAC not to function.  Not knowing the plumbing, I don't know how that would play out.  It would be easy to pull the IAC to check.  Probably the passages should be cleaned, if they have not been.

[Donster]

OK, turns out that now with the new ECM I'm getting error codes.
For the first time I got a 34 (MAP sensor) on 2 MAP sensors, plus the injector I just got is leaking.

Took a MAP off of an Opel, code went away.
Just an FYI: Pulling the battery DOES clear the codes on an 88 L4 ECM.

I did however notice that the PO didn't have a gasket (in addition to the O-ring) on the IAC valve. I found this out by looking at the pictures in the manual for the 87-88 700 TB.
I'll be putting one on today, as that actuall would make sense that it is sucking air around the IAC and causing idle issues when warm, as the IAC doesn't kick in until the engine is warm and comes out of closed loop.
The new IAC only came with an O-ring and I never thought of checking if any other gasket is needed.........so shame on me!
I'll update.

\D

[Raydar]

OK, turns out that now with the new ECM I'm getting error codes.
For the first time I got a 34 (MAP sensor) on 2 MAP sensors, plus the injector I just got is leaking.

Did you retain your same PROM? If not, what is the broadcast code on the chip in the new ECM?

[Donster]

OK, turns out that now with the new ECM I'm getting error codes.
For the first time I got a 34 (MAP sensor) on 2 MAP sensors, plus the injector I just got is leaking.

Did you retain your same PROM? If not, what is the broadcast code on the chip in the new ECM?

Don't know the numbers on the PROM or ECM by heart, as I'm at work at the moment, but I know it was from an 88 Duke automatic with A/C without cruise, so it is the correct one for the car, don't know if the other one was correct though.

\D

[Raydar]

Gotcha. Thanks.

I'll mention that one of the guys on the FB group has an Indy that (apparently) had a hunting idle. He mentioned, in passing, that the installation of the exhaust system from his 85 GT seemed to have fixed the hunting. Said it sounded better, too.

[GTRS Fiero]

Was the exhaust clogged, or something?

[Raydar]

Was the exhaust clogged, or something?

Seems like it, but I'm not sure.
This was a car that he wants to leave stock/original, so I can't see him changing out something, just to be changing it.

[Donster]

Look on the side just below the fuel pressure regulator and just to the left side of the IAC to see if the cap for the idle stop screw has been removed.  It may be that it's been tampered with since you're finding so many other things the OP 'tweaked'. 

Cap had been removed, so I figured, how much more damage can I do if I screw with the screw? LOL
I tried resetting the IAC valve using the procedures I found on PFF and in the manual.
But after taking it out of diagnostic mode with the IAC unplugged, the engine will not start, so I cannot adjust the idle air screw. Is this an indication of a bad IAC?
If I plug the IAC back in, engine starts, but of course with the symptoms again once it runs warm.
And yes, I disconnected the battery, reconnected it, drove for about 60 KM at 35 mph and more, with stop & go and full stops with engine off in between.

That Karmann Ghia is looking better and better! 

[GTRS Fiero]

Ghia not as gun as Fiere.