Where to look next? Feedback/advice?

[944er]

"Im also wondering if an old reference sensor could cause incorrect RPM readings?"

Highly unlikely. The car would not run well, or at all. In your car, the tach is driven by a digital pulse signal from the ECU. Given it is off, perhaps it is sometimes off at times more than other times. Have you confirmed the change in idle RPM with your external tachometer? If it indeed changes, then the engine has to be getting more air in order for the actual RPM to change. Whether that is a subtle intermittent vacuum leak, or the ISV or throttle failing to close completely, something is letting in more air.

[spacecad3t]

"Im also wondering if an old reference sensor could cause incorrect RPM readings?"

Highly unlikely. The car would not run well, or at all. In your car, the tach is driven by a digital pulse signal from the ECU. Given it is off, perhaps it is sometimes off at times more than other times. Have you confirmed the change in idle RPM with your external tachometer? If it indeed changes, then the engine has to be getting more air in order for the actual RPM to change. Whether that is a subtle intermittent vacuum leak, or the ISV or throttle failing to close completely, something is letting in more air.

Yeah. Im aware of all of this- and agree. Just grasping at straws. I'll see how my pressure test pans out.

[danmartinic]

Touch a hot solder-tipped iron to DME & KLR joints with any lines on them

Solved a recent sudden surging issue I had and overall driveability improved noticeably

(I have done this twice now in 7 years on my daily and only driver & each time solved issues I didn't know I had

[spacecad3t]

Touch a hot solder-tipped iron to DME & KLR joints with any lines on them

Solved a recent sudden surging issue I had and overall driveability improved noticeably

(I have done this twice now in 7 years on my daily and only driver & each time solved issues I didn't know I had

No KLR in the NA and my DME is a F9Tech, so its solid-state/refurbished. It would be a loom issue I imagine.

[spacecad3t]

My two cents... I agree with the alternator comment and would want to have the alternator load tested. Some voltage drop is normal when you turn on all the lights, but in that video it just keeps dropping and went as low as 12.2v -- something's not right there. If you have cleaned the terminals and all the grounds, and the battery is healthy, then the alternator is the prime suspect.

On the intermittent high idle, my hunch would be a harness issue -- specifically the wires under the rubber boot on the ISV. That connector is a classic Junior timer just like the speed and ref sensors, injectors, etc., and they all eventually suffer from frayed and cracked wires under the boot. See more than you ever wanted to know about them here:

https://www.carpokes.com/viewtopic.php?t=565

Also, have you reset the base idle? If it is close to the limit of the ISV's ability to control, there may be circumstances where the ISV is able to bring the idle down to spec, and circumstances where it is not. The fact that the idle goes down when you block if off suggests the ISV is not closing as much as it could/should when the idle is high.... My first guess is the connector though...

And I didn't mean to completely discount the throttle body. I doubt it's the cause of the high idle, but I'd still want to reseal it. 944online carries our reseal kits, and the instructions are posted here on Carpokes if you want to get a sense for what's involved.

https://www.carpokes.com/viewtopic.php?t=4972

I have tried resetting base idle several times. Its still nearly closed. Its open 1/4 turn, as I dont see a change between closed and 1/4 turn, and I dont want to bottom it out. If I open it any more, idle just climbs.

[spacecad3t]

Welllll, after a year of testing and fighting my idle, it was my "aftermarket" Idle Stabilizer after all... Im not sure why I had not come across this advice before last week, but I guess you can test the 3 pins for resistance and they should be relatively close, +/- 2 ohm. So I tested the unit in the car, which I installed last summer, 300/21, eek. I ordered a used original Bosch unit from Plyhammer, 20/22, interesting! Installed it today, the car idles perfectly. I can even adjust the idle bypass.

IMG_3281.jpg (1.88 MiB) Viewed 24 times

While I was in there, I took the time to finally replace my AOS, which was disintegrating and had me venting it to atmosphere to avoid the vacuum leak. I reinstalled the hose to the jboot. I also installed the manifold stud kit from 944online because last time I pulled my manifold, I stripped one of the holes. Went all out today, chased the threads with a thread cleaner, red locktite, new gaskets.

IMG_3282.jpg (1.97 MiB) Viewed 24 times

Finally, a rebuilt throttle body, also with studs.
Curtesy of @rheidtman (Sorry Rick, didnt know your username on here)

IMG_3239.jpg (1.26 MiB) Viewed 24 times

Thanks for all the help along the way, very appreciative of the Carpoke community and knowledge!