arpunk

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Feb 6 EDIT: After spraying everything down with carb cleaner to check for vacuum leaks, tightening down intake manifold bolts, and trying different TPS output voltages, I finally gave the throttle stop plate that rests against the screw the TINIEST little bend and now it idles perfect at 600 or so as per FSM.
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Edit: ISA, not IAC

Removed and cleaned throttle body & ISA with CRC Throttle Body cleaner. Went gentle on the ISA.
Reassembled with same rubber gasket from ISA
Put throttle body back on with new Fel-Pro gasket

Checked B terminal for continuity to negative battery terminal: no resistance
Wiggled harnesses: no change
Adjusted TPS to 17% reference reading (.827 for 4.87 reference)
Started Jeep and it idles at about 1,000/1,100 after warming up
OK - started car, turned TPS with voltmeter attached as per @cruiser54’s instructions: idle didn’t move
Disconnected ISA to see what would happen: idle didn’t move

I have the battery unplugged to see if that will reset anything but in the meantime - any thoughts? All vacuum hoses are connected.

cruiser54

How many times have you started it since this work? Driven it?

arpunk

@cruiser54 I started it a few times and let it idle for 15 minutes or so. I took it for a ten minute drive.

After letting it sit with the battery disconnected for an hour or so the cold engine is idling around 875. Let’s see what happens when she warms up.

The FSM appears to show a different ISA with a plunger that sits against the throttle lever. What vehicle is that referring to? Not mine.

cruiser54

4 cylinder.

arpunk

Thanks for the info.

So… idle is steady but a high (1,000ish). ISA appears to be functioning:

Engine on

Engine off

cruiser54

With the engine ON, does the ISA move in and out if you give it throttle and let off?

arpunk

Yes: https://imgur.com/a/lAv9n7S

arpunk

Alright - checked TPS again. It was very close to where it should be but I wanted to get it a little closer and stripped the top torx in the tightening process. Not an easy screw to get to thanks to vacuum harness and 3-pin connector. Anyway - I am still within 1% of spec. Started the Jeep up and it was idling at 3k. Let it idle for a minute or so. Turned off and on. Let it idle for another minute. Started up and still at about 1k. Took it for a drive on the highway and it's still at about 1k.

I'm at a loss for things to try. ISA appears to be functioning as per the video I posted. TPS is within spec.

Is a steady 1k idle consider high for a 5spd 1990? It actually felt a little better on the road with the higher idle RPMs when taking off from a light in 1st.

lawsoncl

The TPS value does change when you move the throttle right? It is possible to get the tab on the TPS on the wrong side of the tab on the throttle shaft, causing it to hold the throttle open and it won't move when the throttle opens. Otherwise, I'd say you have a vacuum leak somewhere now.

arpunk

@lawsoncl I haven’t checked that but I will. I never removed the TPS so I don’t think the lever could have gotten moved. I’m wondering if I could have damaged the TPS by cleaning the throttle body with it attached? I tried to stay away from it and have it facing up so no cleaner would drip down towards it.

Should the tip of the ISA plunger be visible through the hole at idle? I can see the tip at idle and it retracts a bit upon giving throttle and fully when the Jeep is turned off.

lawsoncl

The TPS is very sensitive to aggressive solvents and water intrusion. It's basically the same construction as the volume **** on an old stereo, which can wear out and get "noisy". I would verify that it's still working smoothly with a meter. I'm not familiar with the 4-cyl throttle body and the 6-cyl has the IAC opening a bypass that isn't visible when assemble, but it does sound like yours is working if it's moving.

arpunk

@lawsoncl ok once I get all the dogs I’ll go check the TPS with a multimeter while changing RPMs.

I have a 4.0.

Does this function look right? I thought the plunger was supposed to be retracted at idle to allow air in but this seems to be the reverse.
At idle:

Engine off:

cruiser54

Ever do the throttle body to MAP sensor fix?
throttle body cleaning needs to be focused on the bore, the butterfly and the ISA. You likely messed up your TPS.

74Plb

Or perhaps this one? It worked for me

arpunk

@lawsoncl TPS appears to be functioning properly. What do you think? Ignore the car starting sound - that’s a different car.
https://imgur.com/a/KsbykVJ