Weird idle, what did I do wrong..
 

Hi 911er's,
So, I did a partial engine drop to fix an oil leak, that got fixed great, Yeah!!!
But, I now have a weird idle situation... When it's cold I need to turn the idle screw out a bit to keep it from stalling, then when it get hot, warmed up, the idle is way to fast, 1800-2000rpm's. If I set the idle down it stalls again at next cold start!!!

A few things, maybe narrow it down, when I lowered the engine during oil leak fix, I didn't notice a single wire connected between the upper and lower valve covers and through the tin to a plug right under the gas filter.. It still plugs in but not sure if it broke the plug some how... What is this wire call and for??

Any help where to look would be awesome..
Thanks much in advance............ :)
-Bill

TB, maybe include your location in your sig and post the year of your Targa. From your description sounds like 84-89; based on location & symptoms could be CHT sensor or O2 sensor. Pics and/or further description of plug socket would help . . . .

If you are setting the idle on motronic you must bridge the B and C on test socket with a wire. This is a round piece located on the left panel in the engine compartment. It has 5 holes. You want to bridge the top right hole with the bottom hole. With warmed up engine you then adjust idle with the bypass on the throttle housing. Be sure to remove jumper wire when done.

Yes, My BAD!!
It's an 82' Targa, 3.0 SC with CIS Injection.
I'm located in Meredith NH

Also, Don't see how to ad a signature to my profile??

@targabill -
On Profile page there’s a header tab Control Panel (CP), Sertings & Options - Edit Signature.

Not sure if we are talking about the wiring going through the firewall?

But I had a similar issue with idle and I cured my problems by securing this wiring plug.

So make sure this plug is properly seated:

https://forums.pelicanparts.com/porsche-911-technical-forum/1035497-afr-values-all-over-place-lamb-duh-connector.html

Re-reading your post - the O2 sensor wire comes up through the tin by the valve covers. This informs the Lambda relay located under the passenger seat (lean / rich status).

It should be plugged in - but I dont think it will cause the issue you speak of.

It could be an O2 sensor plug, I didn't note where it is plugged into on the bottom, it has what almost looks like a spark plug wire in a ribber cover similar to how a spark plug wire looks and it plugs in on the Left side right under the fuel filter can. Next time I'm near my car I'll get some pictures..

I looked up the O2 Sensor Here on PP and yes, that is the wire but I think I broke the Male end, the part on the car but I can'r find this?? Any link to this part??

thanks much,

The O2 sensor isn't causing your issue. The engine will run not great without the O2 connected, but it won't run like that with a super high idle. Did you disconnect any vacuum lines? Any other wiring?

I had the same problem with high idle and it was the vacuum lines connected to the distributor one was disconnected and the other had a crack in it. Check all vacuum lines carefully and if possible do a smoke test.

Unmetered Air………
 

Bill,

Test the integrity of your vacuum system. You have unmetered air going into your CIS and a smoke generator is good tool to use to locate these hard to find sources.

Tony

Here is an awesome video if you working on anything CIS related on these puppies..
https://www.youtube.com/watch?v=slCzVrrST2Q

Yes, The very first thing I did was check Vacuum Lines, But this video shows more than I may have looked for so I will be double checking all that...

SMOKE test sounds like a great idea.. maybe another youtube on how to do that.. I'm actually a diehard 356 guy, these engine's are a bit more complicated, but doable::
THANKS for the help guys,

-Bill

@targabill --- I've been watching this thread closely. They symptoms you describe for your '82 SC.

Upon cold start, the rev is a bit anemic at ~ 600 rpm. Then, I adjust the idle screw. CCW, back it out to increase rev to ~ 950 RPM. Then, after car gets to warm temp the idle goes higher ~ 1500 RPM.

I've made sure my timing is correct and all cylinders seem to be firing.

Looks like I should do a smoke test as well.

Have you acquired the equipment for the smoke test? Any suggestions?

Thanks!

Hi Guys,
Just an update on my problem, As mentioned by a few above it was a Vacuum leak.. CIS Fuel system is very finicky if it get some Un-Metered Air into the system. My initial inspection was just a visual look at the lines, one hose, from Distributor, was sitting right next to it male prong, covering it but not actually on it. I didn't feel like investing in a smoker so I went over everything very carefully, although a smoker would of fiunt it much quicker...
Thanks everybody, enjoy your day..

Your symptoms sound similar, except mine went from stalling to about 2500 RPM's. So you may have a smaller vacuum leak.. A smoker still might be a good investment!! Sometimes the AirBox seam might have a leak.. I'll continue watching this thread!! good luck

Yeah, looking at some budget smoke generators, with built in air pump. They are running ~ $150 on amazon. May be I'll just buy one, do the test, fix any leaks, test again to confirm. Then, offer for sale here to members.

If you don't have a good air compressor already I'd suggest picking one up along with a budget smoke tester. You'll use the tester once in a blue moon, but you'll use that compressor all of the time.

You should be able to find a tester kit with fittings and regulators for $60-$80, and a very good (but light duty) compressor will run $200.

@DavidInc - I was thinking about this option as well. Just took a quick look at Harbor Freight's July 4th sale if there are any air compressor deals. If I acquired a compressor, it will be useful for many other things. And, I could even build a DIY smoke generator.

What's a practical compressor capacity for automotive application, in terms of gallons, PSI, and CFM?

I looked at "pancake" style compressors (6 gal, 3.0 SCFM, and 175 psi peak) --- are these practical for automotive applications, or are they really for carpentry?

Thanks!

Compressor cfm should match the highest cfm of any continuous-use tool you have or will get.

an impact wrench, even used intermittently, pulls a lot of air, maybe start there.

Sent from my Pixel 7 using Tapatalk