Why not just command it in and out with the laptop?

I don't have an iac noid light, but I do have a megasquirt I can test iacs with. These iac valves are good.

I'll check the wiring tomorrow.

Car has been messed with, who knows why wires were spliced.

 

Maybe that is the issue. We need to trace it from the ECM to the IAC since someone has some unique ideas of wiring.

 

Yup! I pulled back the loop and there are a lot of splices with electrical tape.. I'll trace and ohm the 4 wires tomorrow morning and see what I come up with.

My ABS light came on today too, but I don't know if that was from putting it in gear with it on the lift (tires off the ground).

-- Joe

 

Yep. I had a mechanic extend the wires for the IAC with butt connectors. One came loose and I could not get my idle right. From then on, I only use butt connectors to test. I will solder if possible, Shrink Wrap Butt Connectors if not. NEVER EVER will I use the regular butt connectors for anything semi-permanent. That thing took forever to hunt down.

I suspect so. One set of wheels were not moving and the other 2 were

 

The wires were fine from the PCM to the iac.

Playing with the laptop, sometimes the pintle moves sometimes it does not.

I re-flashed the PCM to a speed density tune (been wanting to remove the MAF sensor for a while), and verified that the air is all coming through the iac passage.

I dunno. I'm at a loss. I'll toss the new injectors in it when they show up and try again.

Took the car for a drive. Idles at 1200rpm when hot, 800 in park.

-- Joe

 

Injectors came in. Didn't make a difference.

I'm stumped. I'm tempted to try a PCM. I can't imagine what else it could be.

-- Joe

 

I've not read all these post so if this has already been covered I apologize. I had a wondering idle that I could not figure out for some time. I got one of Greg Banish's books and he states that the idle is managed by the timing in regards to keeping it stable by adding and retarding timing. The idle timing is set below peak torque so when adding timing it will increase idle and when retarding decrease idle. I use Tuner Pro and when looking thru my program I found two settings in the "Tables/Functions" section:

Idle Spark Advance versus RPM Error
Idle Spark Retard versus RPM Error

On all the BINS I had on the the 0 error setting in those charts it had 0 timing change. On the above setting 50 rpm error and above it had 5 degrees, even on a stock tune I have for reference. I input 5 degrees in the 0 block and it stabilized my idle. My thinking was if the idle changed 49 RPM up or down the timing didn't adjust, so with 5 degrees in that area if it moved at all the timing would adjust to correct it.

Sorry for the long explanation but I felt it necessary to explain my findings to suggest that your issue may not be air and fuel but maybe timing? Sounds like you've exhausted every possible possible problem in that area. I could be a setting that effects timing after it goes into closed loop.

Good luck and hope this helps. I understand your frustration in dealing with this.

Chuck

 

Interesting info Chuck. I learned something new today.

 

The RPM error table is being hit for sure, if you compare the target advance vs the spark advance table it's retarding timing by the number of degrees programmed in the error table.

The PCM is doing everything in it's power to try and reduce the idle.

I'm really starting to think the IAC driver in the PCM is just pooched. I'm tempted to just buy a used PCM and reflash it with my tune. They are only $200 or so.

-- Joe

 

My suggestion was going to be intake manifold leaks which LT1 are known to have. But in reading all the info it seems you replaced it already.

So out of left field and a guess, don’t be hard on me.

I have seen the opti vary the idle speed when they are going bad or are bad. But this usually comes with a stumble on heavy acceleration in high gear (and at operating temperatures). Don’t know if the opti can do this high idle effect, might be a stretch.

You’ve done all the logical things in all the logical areas. Maybe time to look elsewhere and entertain those lasting comments "it could never be that".

 

Did the opti last weekend. Haha .

Not much original left on this thing..

I took it for a 2 hour cruise today. It's fine driving, but at stop lights it's gonna cook the clutches in the transmission and it takes a lot of brake to hold the car stopped.

Really need to figure it out before I try driving the car in stop and go traffic.

 

Well I don’t mind being laughed at with the effort you put forward so far.


I always like going back to square 1. Did the problem just start one day by itself with no input from you?

How long does it have to be at operating temp before idle goes up?

Will the idle increase just sitting in your driveway as the temp goes up to normal operating?

Did you try this test with the hood open and closed.

If you can get it to do it in your driveway, put a cold pack on the PCM and see if results change.

Does it happen with the A/C on or off (you probably don’t use it in NH)

 

No, I bought the car like this in October. I know it had gremlins and the previous owner wasn't a mechanic, so I offered him $4,000 ('94 comp yellow coupe A4). The high Idle was the first thing I noticed, of course, and then the other issues.

He had wired the fans to the ignition, horns didn't work, some grounds were cut and spliced, aftermarket stereo of doom, a leaking freeze plug, nasty oil leaks, and a few misc things. I've done the following:

Alternator
Freeze plug (the one behind the motor mount, yeah that much fun!)
Intake gaskets (oil leak)
Valve cover gaskets (oil leak)
ASR + cruise delete
Throttle body (twice)
IAC
New rotors and pads
New stereo, proper wiring (haha)
Fixed spliced grounds (that I found - dude used wire nuts)
Ball joints on one side
PCV
New vac lines, and verified proper routing
Tested FPR for leak (sometimes they rupture and leak fuel into vac line)

Reflashed PCM (Fan temps lowered, disabled MAF - switched to speed density)


I think around 165 or so, give or take. It's well after it goes into closed loop, but if I force open loop it has the same issue. When I first start the car it's at about 800 RPM, give or take.

It's really strange..

Yeah, today is the first day the car has been off my lift in a few months.

Yup!

That leads me to an interesting topic. Why is the PCM so hot? Even with the hood open, I noticed the PCM is hot to touch.

A/C isn't charged. Crap, that reminds me, I need to fix the A/C too. haha


Thanks guys

-- Joe

 

Found a thread (3 pages) I had bookmarked on high idle. PCMs unlike ECMs are a much different unit, better and pretty reliable. I never usually suspect the PCMs and hardly remember Forum members replacing them. But there's a first time and you can't rule out anything, just keep them low on the list.

https://www.corvetteforum.com/forums...lue-why-3.html

I know there are voltage regulators, transistors and ICs which many use the chassis as a heat sink in the PCM. It's enclosed, no ventilation and things will run hot. I know with the hood down everything runs dam hot especially in FL. Next time I drive I will take an IR reading for temp.

 

That's a good thread, thank!

I'm gonna order a PCM today.

-- Joe