Per OP's statement post #1; You provided the typical problem sources! Easy to verify by just removing the vacuum hoses.

As another poster suggested….
Disconnect the big vacuum line for the brake booster and plug off the manifold connection. While you’re there, check out the 11 hose clamps and parts that make up the venturi mess.

You can check for vacuum leaks quickest by removing the oil filler cap. If the engine responds, probably no vacuum leak. If no response, probably a vacuum leak.

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I might have missed it, but did you check the runners gaskets?

Serge

I'm not on here very often these days but saw this thread.
You have some sort of idle speed control issue. Can we start with very basic simple test and I assume you have a decent WBO2 gauge.

From here on out disconnect the stock O2 sensor and leave it disconnected till you figure out your AFR issues.

- Engine dead cold
- Do not touch gas pedal
- Start the engine
- At initial startup it needs to idle at around 1100-1200RPM, does it do this?
- As it warms over next 3-5 minutes the idle speed must drop on its own down to 850-900 RPM. Do not touch gas pedal during this testing. Does the idle speed drop as it warms?

Also make note of AFR at initial cold start and then again as it warms it needs to lean out for about 3-5 minutes. After 5 minutes it should be at the target AFR for idle 13.8 to 14.5 range.

The target idle AFR fully warm is 13.8 to 14.2

The other important AFR test: fully warm engine drive in 4th gear at 3000RM on level road and the AFR should be in the 14.4 to 14.8 range. This test is super simple, very stable condition and gives us a good idea of what the mixture is. This test is important as it does not care about idle quality, we just want to know if mixture is in the correct ballpark at part throttle cruising load.

Report back on these tests and we can continue.
Also email me at sal.carceller@cox.net and I'll send you some docs that may be helpful.

One more test, get a timing light and check timing at idle fully warm. It should be set in the 0-10deg advance at idle. But I have no idea what aftermarket chips may be doing here. Do you have a stock chip and use it in the stock DME. The idle timing must be stable and not jumping all over the place. Let me know if you can check this.

Just saw your videos with LM1 WBO2 gauge. Please tell me that the WBO2 gauge is not in the tail pipe. The WBO2 sensor must be installed in the stock bung to get accurate readings. In the tailpipe it will read significantly leaner than in the bung.

Your suggestion is the easiest and best suggested in this thread as I implied up-thread, but appears to not having been tried.

Seems suggestions fall on deaf ears!

Agree, if either of those leak fuel from the vacuum port you will have false fuel entering the intake. Super easy to check and is worth checking.

From the first post this was stated:

Since making all the other changes, did this ever get put back to factory setting? Whole lot of changes made over the course of this "project" without returning to baseline.

I'm kind of confused because you've pointed out the big huge glaring problem right there. "Rebuilt DME runs like crap" and "original DME runs great (but needs idle adjusted)".

Almost all of the troubleshooting is done right there. Why mess around with a known crappy DME even if it is supposedly "rebuilt"? Go with the DME that is clearly running well.
- If you are set on some sort of mod like a 28 pin chip with a different map in it: Do that with the DME that works correctly. You can easily swap in and out a chip and you are changing one thing at a time so you KNOW what is causing the issue.
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I would get the original DME back in there with a stock chip, get the idle adjusted, and then you can mess around with whatever mod you want to play with and you will know that any changes are only caused by your mod.
If you want to retain the rebuilt DME as a spare or to swap it in at some point you need to put a stock chip into it and then get IT (not the rest of the car) to a point where it works well. Once the basic unit is working in a generic configuration then you can work on whatever mod it has on it.

Hi all,
Just catching up on the thread. Thank you for the great input. Here is where I am at (along with answers to the various questions).

Symptoms:
High idle when warm .. with SW chip idle is 1,200 to 1,300 when engine is fully warm. IACV is being closed by the DME. Idle bypass adjuster is full in.
Idle flux when warm with stock ’89 chip. Idle is ~ 1,000 before the engine warms enough to start fluxing. Mode would be something like this.. cold start would correctly fast idle .. then drop to just a little high .. ~950rpm … then as the car warms the idle will creep up. Fully warm, I get ~ 1,000 or so idle that fluxes until you “settle” it back dragging the engine down.
High RPM miss in 2nd gear at 6,100 rpm and will not rev higher (like a rev limiter).

Replaced list:
DME, IACV, Head temp sensor, Crank speed and Ref sensors (re-set gap to flywheel), 02 sensor, oil cap, various vacuum and vent lines, spark plugs, FPR and Fuel Damper

AFR testing: I am using a tailpipe mount for the WB sensor. I do not have a catalytic converter (Fabspeed test pipe installed), so my thought is the Innovate tailpipe mount should be OK?

DME: Car came with the original DME but was chipped with an Automotion chip from the 90’s. I ordered a “rebuilt” DME that was clearly defective .. that’s why when I put the original DME back in, the car ran “better”.
I now have a correctly working Focus 9 DME with both a stock ’89 chip program and a SW Chip. I’ve been running the SW Chip because .. 1) no idle flux and 2) the tune is sooooo much better than stock. The new DME did not correct the high idle issue.
For further testing I’ll put the ’89 stock chip back in.

Updates:
I replaced both the fuel pressure regulator and fuel damper .. cause I’m thick headed that way. Both parts removed appeared to be original to the car… and I believe both were operating just fine. With both the FPR and Fuel Damper, the idle is still too high .. although a little smoother (or my wallet is telling me the idle is smoother).

While changing the fuel damper I found the vacuum line to the … err … “carb de-icing” / ambient air valve was very loose (oversized vacuum line). Sorry .. I don’t know the proper name, but it is a vacuum line + valve + vent line setup that as I understand brings in an alternate air port (from the oil tank) into the throttle body when temps are below 50 degs to prevent icing. I took the whole kit out for my testing and plugged up the ports. Sadly .. no impact to the high idle. I do plan to put this all back once I have the issue sorted. I assume the engineers put that mess in there for a reason.

I tested the idle switch .. works as expected and measures in spec. Removing the connector the idle jumps up from +500 rpm (to ~ 1,700 or so) .. putting the connector back on brings the idle back to the 1,200/1,300.

I disconnected the throttle linkage at the transmission .. no impact.

I disconnected the brake booster hose (and cruise control line) and plugged the open line. No impact (and happy to see the brake booster line has been replaced)

So … where is the engine getting the extra air from to idle high?!? I’m back on the vacuum leak train of thought ….
I broke out the smoke tester I got from Amazon. New videos posted for your enjoyment (same link):
https://www.icloud.com/sharedalbum/#B0mGGXqixG0EmhB

I did find smoke leaking at the elbow to throttle body connection .. I’ve had this off a few times, looks like that clamp needs to be tighter than I thought. I tightened and no more smoke leaking there.

My new (OEM) cap is leaking a lot. Seems odd. I put the original back on, and it leaks much less .. but still seems to leak a little when I have the intake fully pressurized (via the smoke tester). Is this normal? I put a little oil on the cap threads and a little oil on the gasket and that reduced the smoke coming out some .. but still a little coming out.

I was expecting to find something more .. but that’s it. Note, the video’s may be a little misleading and there are few times the intake plug came loose letting some smoke out (not leak related).

The hunt continues!

scarceller, thank you for chiming in!

Next:
Put ’89 chip back in. Resent FQS to stock (position 1). Disconnect the 02 sensor. I’ll adjust the idle bypass 1/2 turn out. Leave the AFM as it (~1 turn out on the idle mix adjustment .. as I recall) .. monitor the current A/F ratios and rpms at cold start and warm up.

Other troubleshooting ideas…
What is the purpose the “U” vacuum line that connects the thermo switch on the back of the throttle body back to throttle body again. Is that for cold start or just for additional air when the throttle body alt air / de-icing is engaged? I’m thinking of removing that and plugging up both ports to see what happens.

AFM .. could a bad AFM cause these issues? That’s on my parts to replace list.

Timing … could the distributor be installed incorrectly causing the timing to be advanced? I may get my timing light out and see what the idle timing is showing as.

IAC Valve .. seems like I should be able to get correct idle speed with this at 1/2 open. What I’ve noticed, is the DME closing the valve as much as it can .. but I feel I can further close the valve a little bit more (manually) and further bring the idle down… this is like going from 98% closed to 100% closed. Could this just be my cheap IAC isn’t to spec?

I’ll report an update later this weekend.

Thank you!
Chris

http://forums.pelicanparts.com/porsche-911-technical-forum/360766-bench-testing-carrera-idle-control-valve.html

Yes, read post #20 for a very simple test.

Interesting update from latest idle testing.

FQS confirmed currently set to 0
DME back to using stock 1989 3.2 chip
O2 disconnected from DME
Wideband now properly mounted in the O2 port

Interesting finds:
Idle A/F ratio now looks good (or perhaps my pervious measurements were incorrect)
The drop from “fast - cold start idle” seems to not be happening as expected. Only about 100 rpm drop when warmed. Hummmmmm.

Cold start test (car has not been started in a few days .. about 60 degs out):
Two videos uploaded to the album …
https://www.icloud.com/sharedalbum/#B0mGGXqixG0EmhB

First is about a min after the cold start (I thought I started recording earlier .. but didn’t hit the button.. doh!). Anyway, the idle was still in the “high” mode .. and only drops about 100 rpm once warmed. You’ll note the A/F looks good starting at 13 to 1 during enrichment and running about 14.1 or so when warmed.

Second video is with the car warmed past cold start (but not fully hot). This is where the idle starts to flux. A/F looks good. Seems like the issue is fast idle isn’t dropping as it should. Thoughts? How does the fast idle work?

Thank you for the input on the IACV. I did test it per the other post and it works … opening and closing without any noticed sticking. It is a new unit (China mfg).

Next up: Running test of A/F ratio to see what that is.
I’ll be reading up on the fast idle circuit and see if I can manually disable that as see if that drops the idle.

Thank you!
Chris

Hunt. Try adjusting the idle down by turning the air screw CW in the throttle body, and not adjusting the idle screw per the jumper switch procedure.
If that doesn't solve the problem, then there's an air leak somewhere bypassing the throttle butterfly.

If you do use the idle setting procedure, i.e. jumper/switch, the DME ECM will set the idle valve at 50% allowing the idle to be set very low with the adjustment screw.
If the idle does not adjust to a very low RPM, this will further confirm an air leak.

Hi Dave,
I do have the air screw on the throttle body fully turned it. No adjustment left.

I agree .. somewhere air is getting past the throttle plate. I did an intake smoke test (videos available at the leak), and addressed the few small leaks found (no impact). Now I am thinking the issue is there is air bypassing the throttle body plate internal to the intake system. Throttle plate not adjusted correctly or throttle linkage hanging up the throttle return are possibilities .. although I have do some checks for these issues and the throttle plate seems to be fully closing (although I have yet to pull the throttle body for a more proper inspection).

My latest thought .. could the thermo switch be stuck open and would that cause air to bypass the throttle plate? I'm going to pull the vacuum line off the thermo switch and plug it to see what that does.

Thank you for the collective think on this. I feel when I figure it out it will have been obvious.
Chris

Just remove the air cleaner and cover the throttle body intake.

I helped Chris out figuring out this hi-idle issue. He had been using an aftermarket Idle Air Valve these valves do not function like the stock OEM Bosch valve. These valves when fully closed still allow significant amount of air through the valve while a properly functioning OEM valve seals completely when closed. The main cause of the hi-idle was the fact that the non-oem valve was flowing air even when closed. Even when fully closed and the idle speed screw on the throttle body fully closed the idle speed was not at 800RPM or less. If the valve is fully closed and the idle speed is still high you can't expect the DME idle control to do magic :(

Lesson learned here, that I already knew, non OEM parts often are not the same spec as the OEM part.

Also, do not just start throwing parts at the problem as you often can make things worse by introducing yet another new problem.

His original ICV was defective after years of use. But then he put a non oem valve into the mix.

I'm hopeful he's on his way to solving this.

The suggested tests in posts #33 & #34 would have indicated a bad valve. Obviously the OP didn't actually do the tests he claimed he did, or he did them incorrectly.