Up & down idle 88 Duke when warm

[Raydar]

Doesn't the MAP sensor also control the fuel pressure regulator, or are they just both connected to the same intake vacuum port?

On a V6, they're just connected to the same vacuum source. Not even sure about the Duke.

[Donster]

I think I've asked this before; does a bad MAP "always" throw a code?? If I disconnect the MAP cables (not the vacuum), the car idles fine and stable. Unfortunately, it lights up the Check Wallet light and sets code 33 or 34. I plug it back in, the hunting idle returns, but no codes.  

Doesn't this sound like a bad MAP sensor??

[GTRS Fiero]

Yes.

[Donster]

OK, please help me out here. I've got a new scanner, which works for ALL models of Fiero, Firebird, P6000, Camaro, Cavalier, Celebrity, Citation & Corvette (yes, also for the 87-88 DIS Duke  ).
Below are the scans from the warm engine, no trouble codes, what am I missing?



Thnx!

[TopNotch]

I'd like to know where you got the scanner.

[Raydar]

"IAC 34/34", I would sort of expect that to be moving around, as the ECM attempts to adjust the idle.
I don't know exactly what the reading means. Could be 34 of 34 "steps" (which would seem to indicate that something is maxed out) or 34 steps one way, and 34 steps the other way. (34 is a strange number to be a maximum. I would expect 16, or 32, or 64... something like that. Just thinking out loud.) 

For what it's worth, when the engine is cold, the O2 sensor reading should read a steady ~.445 volts. It should also show "not ready", I would think.
Once the engine is warmed up, the O2 sensor should bounce around between .1 volts and .7 volts. Probably too rapidly for you to even read it.
If it's just sitting at .106, the O2 is either lying, or the engine is running very lean. I notice the "Mix / lean" reading. I would think it should be bouncing around, too. But if the O2 is sitting at .106, the "lean" flag would be expected.
(I had an O2 sensor to fail, in that manner. Was reporting "full lean". In reality the ECM was just dumping fuel in. It was running so rich that it would burn my eyes when I stood behind the car.)   
 
I wish Ron was checking in. He could provide some valuable insight.

[Donster]

Items with two readings = 1st at engine start up, 2nd actual value
Hence, IAC was at 34 steps at engine start-up and at 34 when measured.

[Donster]

I'd like to know where you got the scanner.

Home made by a member of the German Fiero club.
Kewl thing is, it gets its power via ALDL port while scanning OR via USB port, but also has batteries.

[TopNotch]

[Home made by a member of the German Fiero club.

Oliver Scholtz?

[Donster]

Oliver Scholtz?

Who else? 
This way I could be assured that it works. And it is very professional looking!

[Donster]

As awesome as it may be, it is worthless to me, if it won't help me narrow down my issue!

[Raydar]

As awesome as it may be, it is worthless to me, if it won't help me narrow down my issue!

Pay attention to what the O2 sensor is doing, as posted above. It needs to be switching back and forth.
Assuming the scanner reports readings in real time.

[Donster]

Rained all day, so I couldn't really do any engine work. I'll run another diagnostics tomorrow.
Also was told, an incorrect thermostat can possibly cause hunting idle. Weird. 

[Fierofool]

I saw your question and the answer about the thermostat.  The temperature is usually on the bottom of the thermal bulb.  I think I've only seen 1 where it was on the flange.  It has become a common practice to drill a 1/8 hole in the flange if it doesn't already have a little weep valve pin in it.  I don't remember why, but I pulled both of mine and did the mod. 

[Donster]

It has become a common practice to drill a 1/8 hole in the flange if it doesn't already have a little weep valve pin in it.  I don't remember why, but I pulled both of mine and did the mod. 

Can somebody post a picture, of where exactly the little hole needs to be drilled?