Petza914

Since the high idle only occurs after the throttle is pressed, it really sounds like a mechanical binding of the throttle, but I know you said you already tested the mechanical part. I think ISV would be the next place I'd look or the MAF.

Boaf 32

Thanks Petza914. I have the old ISV (now working) and will install shortly.

@Petza914 Is there a Throttle Body rebuild kit out there in 928 International or 928 specialist? I'm checking but not seeing anything. In the very first post #1 I had a backfire that blew out 2 anchor screws. The backfire was strong enough to break my air filter and dislodge the intake tubes(the rubber attached mixing plenum) on the passenger side. While I'm ISVing, will see if I can check the butter fly for any wobble. Thanks.

Boaf

Petza914

I'm not sure. I'm a 16v 928r but my 944 S2 is essentially half a 32v 928 and has an ISV, but I know the older 928s much better.

Boaf 32

All,

Update: I had the LH Tested by Dave (see #30). I have a new and an old ICV. I tested both installed and both had the same results. Tested them outside with a car battery as follows

Old unit (cleaned out and lubricated):

• Red hot middle connector
• Valve 1/2 way closed
• Touch negative to the right side connector and the valve closes
• Touch the negative to the Left side and no movement. The negative test lead is a light tester

New unit:

Same results.

So the question, do I need to test the unit differently? Should it open when I connect the negative to the left side or is that governed by pin 33 and the other by a ground resistor in LH? See this great thread #13

I tested the Throttle body for air leaks, removed it and plugged the vacuums and blew into it and no leaks, my eyes almost popped out.

So will re-install the old ISV, (after responses to this thread) with the recently tested and working LH Unit. Will check for binding throttle cable by not connecting it to the Throttle Body. I'm about to send to the professionals but don't want them to repeat the exact same tests. Any other thoughts are really appreciated.

Boaf

Boaf 32

Hi gents, question.

As you know, been battling a high idle issue. Took these photos of the Throttle body with a flashlight underneath. 2 questions.

1. Is there suppose to be a gap in the butterfly? You can see the light in both photos. I think that gap is for an idle but not sure.
2. The photo from the bottom, there is some discoloration outside the rubber seal. Do not believe it is a leak and the rubber seal is in tact (replacing seal while it is off). Any thoughts on that discoloration?

Thanks all.

Boaf
TB Top

Looneybin

still following your progress as my '86 is still doing the same thing
currently have the intake off to replace the ISV

Boaf 32

Better picture of TB from Bottom. Notice the discoloration at the top. The rubber gasket is in tact, different though than the new one, the old one is square top. Believe that is correct.

Boaf

Petza914

I can't imagine that plate isn't supposed to be centered and the idle screw just opens it slightly. The way that looks there's no way to close down the airflow and lower the idle, but maybe they're all like that - just looks like it shouldn't be.

Following for those who've looked and can definitively say.

Mrmerlin

that gasket is a round O ring that compresses to a square after many heat cycles,
I use DC111 on them to prolong their life.

Its too hard to see whats going on with the throttle plate,
but I think it should be more closed than it is.

I would remove the TPS and place it on a few paper towels with the shaft opening facing down, see if its full of oil,

if so then you should replace the throttle shaft bearings with the new double O ringed versions ,
and consider replacing the TPS and the short harness to the TPS,
Roger sells them

sabres32

I had similar issues with my MY85, I replaced all the major parts, chasing a high idle. Obviously vacuum leaks also need sorted first. I also blamed the Lowe ISV and even purchased a Bosch from a 80s BWM that was the same as found in our 928s. No change in my situation still a high idle running rich. I became an expert in removing the intake chasing my issues. After watching videos and learning how to read the wiring diagrams and testing all my connections. My issue was the short TPS harness cable I purchased from one of our community vendors. The wires were revered where it plugged into the wiring harness next to the test port, one in a thousand I'm sure, but that was my final issue. Once I solved that, all my idle issues disappeared. I built a Porken Blink'R and tuned my air fuel mixture. Been enjoying the car taking in on a 6 hour round trip drive with no issues. Now I'm working on other issues like the HVAC, radiator leak, etc.

From my experience working on my car, make sure you're not just swapping parts, test the parts, check the cables and connections. The multimeter and the wiring diagram is your best friend! Good luck!

Boaf 32

I shall. @Roger do you have these o ringed throttle shaft bearings in stock? I have replaced the TPS.

Boaf

Mrmerlin

Roger sells the new O ringed bearings

Boaf 32

Fellow 928ers,

Update:
I decided to rebuild the throttle body based on not wanting to have to go through this again. The retainer was a challenge, my retainer removing tool was too big. Improvised using two scratch awes, very small screw driver, and taping the shaft out gently. (Patience Obi Wan)

@Mrmerlin do you have rogers contact information or forum name @Roger ? I do need to replace some parts (Plastic crumbled in my hand) including those o rings you indicated. See attached. I'm not sure how the shaft bearing comes out or if it is needed, not a lot of play. Any guidance there is greatly appreciated.

Boaf

Petza914

Roger is @ROG100 and his business is www.928sRus.com

Boaf 32

.
Ahh, Thanks I know him... Spoke to Roger today. that black piece that goes under the return springs is not available. He suggested 3D printer. Will update all after assembly.

Boaf