The pictures did not turn out like I had hoped. But here is the story.

A couple years ago I had my TB rebuilt. Yesterday I used a smoke machine on the FI system. Found nothing of real consequence.

The problem is that if the engine is not too hot, at idle it goes down to 1400. 90 seconds at a stop sign or coasting and the RPM will drop to about 1000. Now that is what happened today and has happened since I started driving. seems right, but takes a while.

If the engine is good and hot... OT around 240, air temp 90+ idle will quickly drop to under 1000 and sometimes die. Gonna drive tomorrow and see if that continues.

the pictures are the idle adjustment screw. I noticed today that it would turn with ZERO effort. it looks like the plastic in the threads is taken on the shape of the threads and no longer holds. Can I buy a brand new screw?

I did replace the o-ring today. You can see the btm picture, it is a bit fatter and seemed to hold slightly better. No real change.

What can I try next?

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Standard answer but is your advance plate in the dizzy free and moving easily,also make sure when you apply vacuum to the canister the advance plate snaps but quickly when you stop sucking on the hose.
The TB screw has the nylon insert to create friction on the screws thread,the oring is to prevent air leaking past the threads from memory.
Air you still running a deceleration valve?
L-jet is very sensitive to air leaks so if your TB screw isn't responding you may still have an issue there.

Thanks. I’ll check the disty. Decel is gone. Port on the air dist. iis plugged
As I mentioned, I did a smoke test on the fuel injection system. The few smoky spots I found I fixed.

I would try to heat up the plastic a bit to melt it and distort the threads. You can also try to turn it a bit.
Also, there is a thread locker that doesn't lock but just adds friction. I don't remember which one exactly.

I talked to Phil, the guy that rebuilt the TB. His info: the screw did not come with an oring. He machined a place for it and added one. He approved of my fat one. He also said i might drive the nylon plug out. Very carefully so as not to damage the fine threads. Then cut it in half and add a spacer. I like your idea of turning it. But 90 degrees will not leave it round. And these are un-obtain-able.

I also thought of the light duty thread locker which is easy.

You can replace the nylon insert pretty easily and I don't think you don't need to worry about not damaging the threads, in fact, it's probably better if you do. The nylon is soft so the threads get cut into it when you screw it in and lock the screw in place. Here's a link to how I added my own nylon thread locks for custom shift linkage bolts.

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I made some time to mess with this tonight. Help me out here... I pull "A" and give it a suck and the disty innards move quickly and decisively. Is that the advance? I gotta look up the plumbing, but is it correct?

"B" on the other hand DOES NOTHING. Sucking or Blowing. Almost like there is a hole inside the can. I pulled the whole hose and plugged one end and get suction, so it is not the hose.

Remember the OP here was about what the engine does at idle. Sometimes 1400 at a stop light, sometimes 1000, sometimes 800.

THoughts???

The pencil drawing is correct. This is me.... although I have removed the EGR and Decel. And never installed the charcoal canister.


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double post

I may have cleared this up. I started another post about the vacuum can and received an offer to try out a known good disty. So I did.

Got it installed today, timing and idle set and went for a drive. The idle drops to @1000 at every stop sign.... PERFECT.

There were several variables in this changeover, so I am not positive which one fixed it.

different Bosch model #s, non-leaking vacuum can, petronix vs hot spark..... But hey, it seems to have fixed the erratic idle condition.

We will see for sure as I drive to work next week.


Thanks Joe @porschef ,

Clark