Fast idle fixed easy repair

[BeeBeeper]

First of all I have a 1982, SC Targa, 3.0 Engine with CIS with Lambda. Original 46,000 miles and in perfect showroom condition.

Well folks, I have worked 6 months to fix the fast idle problem with my 911. First of all I must say that when I bought the car it sat up for about 4 years in a wharehouse. This is not good for a Porshce.

I started the diagnosis for the fast idle using many of the suggestions from the forum and other books I have obtained. These were great suggestions and I learned a lot in the process, even though my solution was never suggested and I did not read this anywhere. I discovered it myself after many months of trying to get it right. Hopefully some one can use this solution and save themselves a lot of grief, time and money.

My diagnostiic work went through the process of checking out the WUR, AUX, Decel Valve, cleaning the distrubutor, trying to find air leaks, dismantling the air box, changing all the rubber boots, changing the coil, perma tune box, changing the chain tensioners to hydraulic, changing the vacuum hoses, changing all the boots ont he CIS injection system ,experimenting with the timing and of course experimenting with the CO.

The solution ending up being a little easier and cost me nothing. I notice that the idle of my car varied from time to time. One time I would stop at a light and it would be 1800 RPM'ds, the next time it was 1200, the next it was 2200. I noticed however that if I put my foot on the brake and let out the clutch while in first that the idle would always go to around 950 RPM.. I figured that it was something sticking but could not figure out what.

When I opened the air box and took out the filter I would notice that when I was trying the set the CO with a CO meter that I was getting varying results. When I moved the allen wrench, the RPM's would change. I did notice that if I pulled down on the part that hangs down in the air box that I felt that I could have set the idle if I could keep it there. I also noticed that when I would take the allen wrench out of the set screw area that the idle would change. By reaching up under the air box I could feel the round sensor plate that allows the mixture of air and fuel. I felt around the edge of the cylinder with my finger with the car not running and noticed a gummy substance all around the edge. I wondered if this was causing my problem. I got some "Gunk"(degreaser) on a rag and wiped all around the outside area of the cylinder. Voila, there was a lot of gook around this area. I notice immediatley that that the sensor plate moved freely and would travel further south in the cylinderwith no resistance. Infact, it cleaned up things so well that my car would not run. I had to reset the CO and the idle screw on the car.

Long story short , this fixed 6 months of diagnosing a fast idle problem. I guess there was enough gook to prevent the sensor plate to set right and not allow the proper air flow and was difficult if not impossible to set the proper idle or CO for the car.
I also unscrewed the idle srcew and took it completely out and noticed the same kind of gook on it. I took a wire brush and cleaned this also and reinstalled. This helped the setting of the idle.

I know that this process worked for my car and may not work for all because after 6 months of diagnosing the CIS system it is complicated enough to get a little frustrated. There are other areas that can cause a high idle problem. If you have gone through the diagnostics and can't find a leak and all the valves, etc seem to be working, and can't find any leaks ,try this. It takes about one minute and can save a lot of money and greif.

The good news is that when I set the timing , set the CO per my analyser I not only get a perfect idle, but also the car performed like a scalded rabbit.

I knew that if I worked on this long enought, I would get it. . Try this procedure and you may get lucky and have the same problem. If you have any questions, please contact me at : Lanscor@cox.net.[img]

Ron

[Paulporsche]

Congratulations on an easy and cheap fix. Sometimes the obvious things get overlooked when discussing diagnoses on the board. We'll have to always include "Make sure the sensor plate is clean and able to move freely".

[steven polaski]

Hi Ron

Just a question about the idle problem you had. My 930 does the same thing until I let out the clutch a little . If I tap the gas it still stays high do you think it's the same for a turbo ? My car sat five years also.

Thanks Steven

[BeeBeeper]

Steven,

I am sure the throat of the 930 intake manifold is similar. I would seem to me that if you can let out the clutch which is putting a load on the car and the idle goes to where it suppose to be, this would indicate something sticking. Also if a car sits up for a long time the fuel turns to varnish which quite sticky. There is a control piston in the fuel injection manifold. This is the black piece that all your injectors tie into. The middle of this mechanism has a control piston, however you would have to take off all the injector lines to remove it. If this is sticking in various positions, this could be your problem also.

You did not mention the year of your 930. I have never worked on a 930. Does your car have an intercooler??? I would assume if you have an intercooler , you can remove it check you sesor plate to make sure you have free movement. It should move freely up or down. If it seems a little sticky like mine when you push it up, clean around the inside of the intake manifold to make sure the plate sits all the way down with easy movement.

Good luck. If I can help in any way please let me know.

Ron

[steven polaski]

I have a new fuel distributor for my cis so it's o.k. I will take off my intercooler and clean up idle screw and sensor plate. Thank for the help Ron by the way I have a 86 930 found it in a barn sitting for fivr years paid $ 4,500. runs good !

[KCPSG]

Ron, Very nice car...I haven't seen you around Lafayette w/it yet.

I hope to soon,

[johnco]

BeeBeeper, nice looking car. I live in Morgan City and get over to Lafayette all the time. If you ever need some help with anything, let me know. I'm bored when I'm not working. Or if you're ever over this way, stop by our wine shop. it's called Le Bon Vin

[jbrinkley]

4.5k for '86 930? That just isn't fair, in fact it's cruel.

[BeeBeeper]

Steven,

Finding a 86 930 in a barn for $4,500??? You lucky dog!!
Find me one please. Did you find in an ad or did your car break down and had to be nice to the farmer's daughter. Come on! I got to hear this story.

Good luck on the car. I wll give $5,000 sight unseen!!!

Ron

[azasadny]

Ron,
Great writeup, thanks! My car is doing the same thing but the sensor plate is clean and moves freely, I'm going nuts trying to get my idle to stay around 950, but no luck so far...

[jgporsche]

Great write up RON!!!

[steven polaski]

My problem stems from being stupid, I left a blue cleaning rag in the intercoolers inlet pipe so when I put it back together no turbo so I pull open the turbo inlet and there is part of my rag the other part went through ( in small pieces ) the turbo and every so often getting stuck in the throttle body hence high idle. The car's story is here so do a search on my name and you should see a lead about the car and the price.

[azasadny]

Mr car now idles around 1000rpm, but as soon as the car reaches operating temp (180 degrees), she idles at 2000rpm...

[BeeBeeper]

Art,

Your problem sounds like your auxillary air valve is not closing. The auxillary air valve has a heating element in it to enrich the mixture during warm up. After warm up however, the valve should close. If it does not close for some reason, the idle will remain high. Try plugging the auxillary air valve with a peice of rubber over the pipe and then reconnect. See if this helps. If it does, you can rebuilt your Auxillary valve. Look for the Post, "Auxillary Air Valve revisited". Check your electrical connections before you go through the rebuild.

After your car has warmed up, take off the hose to the auxillary air valve and take a mirror and line it up so you can look in the valve. Your valve should be closed. If it is not then your valve is not closing or check your electrical connections to this device.

Also, I have heard that if your Warm Up REgulator (WUR) is not functioning, this can cause a similar problem. The CIS system is somewhat confusing in that some devices mimick others, so you have to diagnose one at a time.

Keep the chin up. These problems are sovable if you stick with it long enough.

Ron

[Paulporsche]

Aside from the Aux Air Regulator, check your Decel Valve. Try disconnecting the hose on the top and plugging it and the open nub. Also check for any other air leaks. And make sure your control pressures and mixture are correct (not too lean).

Ron, you are describing the AAR not the AAV. The AAR does not enrichen the mixture at all (that's what the WUR does). It regulates air bypassing the throttle to keep the revs up during warmup. The AAV does the same type of thing but only during starting.

[BeeBeeper]

Paul,

You are right. Thanks for the correction. I should have put AAR instead of AAV. Also I noticed that Art's car is a 1974 which may a completely different set up. Isn't the decel valve behind the air box??

Ron

[Paulporsche]

Check out this exploded view:

http://www.pelicanparts.com/911/911_Parts/1974-75/2-3-1.JPG

[azasadny]

Thanks for the info I have replaced my WUR, but I don't have a AAV on my car...