Benjemin Bale

Hello all, I finally brought home a 1986 930 wednsday and I have a bit of a problem. After starting the car and driving for a while (at least fifteen or twenty minutes) and turning the car off for any amount of time. When the motor restarts it idles to 2200-2400 RPMs for about a minute and then settles back down to between 900-1100 RPMs. It acts like it is in the cold start mode. The car has the following mods,rebuilt motor with approx 2000 mls,leakdown was 0-3% accross the board,twin plugged heads,electromotive tec 3 direct ign,38mm ported heads,sc cams,k-27,1 bar spring, Andial IC,new injectors. The high idle seems strange to me. When I had the PPI done on the car I asked the mechanic if this was normal and he said thry all do that. Any input would be helpful, Thanks Ben

Mark Houghton

It's normal for the 930's to return to a higher idle even after shutting off the engine for only a few minutes, but maybe not so high as yours. The symptom is caused by your auxillary air valve. It's located to the right rear of the intercooler, connected to the intercooler via about a 1" diameter air hose. It's function is to let in a small amount of air to the intake when cold, leaning the mixture just slightly and raising the idle. It has an electric heating element that will usually within 3 minutes begin to close the source of air and drop the idle. 2400 rpms sounds a little high, but I have heard of others whos cars idled that high. Mine settles in at around 1800 initially. Yours sounds like it's working as intended, but idling a bit too high.

Pull the hose off the front of the AAV, and look inside with a flashlight. When hot, you should see only a small notch on the flat disc in there, letting minimal amount of air in. When cold, the disc will have rotated sufficiently to open up a larger area of the hole.

You can also bench test the unit by removing it, placing in the refrigerator for awhile to make sure it's cold, then view the slot inside. Hook up 12 DC to the electric plug and see if the disc moves closed. Alternately, put the whole thing in a warm oven.

As far as adjustment, I understand that there is a drift pin on the AAV that can be driven in or out to change the spring tension which governs how much it opens. Risky experimentaion in my mind. Another option that should work (though I've never tried it), is to put an air valve in the hose leading to the AAV, and simply close it off as needed when cold to achieve the idle that you're comfortable with (you can demonstrate the effect on a cold engine by clamping the hose closed after starting the engine...the rpms will drop way off).

Finally, make sure your mixture at idle isn't running too lean. The additional added air from the AAV may be just enough to lean it out even more and cause higher-than-you want-idle. Oh, and don't forget to set your basic idle to factory specs (for your '86 I think it's 900). If you're motor is settling in at 1100, you can effectively shave off at least 100 rpms or so.

Benjemin Bale

thanks Mark, I will try your suggestions today. I just cant wait to get it out again, I know I have only had the car a few days but the bug has bit me hard. Thanks again, Ben

Cajun

I agree with Mark, and your mechanic is also on the money. My car does the exact same thing, but the "high idle" is around 1500-1800rpm.

Post pics when you get a chance!

Benjemin Bale

Ok, I checked the aac and it appears to be working as intended. The idle gets progressivly higher the warmer the motor gets or the longer I drive it. When warm it starts fine at about 1800 rpm,s and steadily climbs to now 2700-3000 rpms. I will try putting a valve in the line today to close off the air supply and see how that works.

jetskied

you probably have addition air coming in through some type of vacum leak. Make sure all conections are tight. One other thing a CSI engine may have a problem with is the CSI weight balance or some will call it the fuel metering plate. If it is not adjusted properly or is very dirty on top it will keep the idle up. I had a dirty top on mine and it would have similar symptoms to yours, but may was at a lower RPM 1800.

Benjemin Bale

What would the csi weight balance look like? Is it the plunger under the air box intake? I started taking things apart Monday (cant help it I like to know how things work) and found a bad seal at the intercooler-turbo up-pipe connection. Its the orange oring around the ic neck, I only had half of the seal left. Could that be a vacum leak source, I was probably loosing boost also from that. It will be a week or so untill the car is running again due to mods on the way. I thank every one for the advice and will post some pics of the car as soon as I can. Ben

DougM

Ben
You should mention that the idle slowly fluctuates up and down while it sits and idles.

Mark Houghton

Ben, if you've got a leak in any of the orange o'rings, that will result in pressurized air leaking out. Now, realize that that air originated from the air box and as it passed over the plunger in the fuel distributor(and deflected it downwards), it set up the correct fuel delivery based on the air flow and deflection it experienced. So, your mixture is all set and balanced with the amount of air supposedly going to the engine. But wait!!!.......now some of that air is leaking out before it makes it to the engine. The fuel delivery hasn't changed, but the amount of air going to the engine has decreased. The result: We're running too rich now. That in itself should normally cause a lower stumbling idle. So, keep looking for an air entry point directly into the intake manifold someplace after the intercooler. These turbo CIS systems work opposite than standard non-turbo, where an air leak would normally cause a lean condition.
Hard to explain...maybe someone on the board can do a better job. Get your hands on Bosch's Fuel Injection and Engine Managment bookl (Bentley). It covers the K-Jetronic and other systems, full detail on how that mysterious marvel works.

nathanUK '81 930 G50

I would guess that at idle the car would run lean due to umetered air getting in to the engine. When on boost the car would run too rich due to metered air escaping the engine.

Benjemin Bale

Ok, I've been all over the car for the last week looking for problems like loose lines ,wire connections or anything else that could be a problem either now or the future.(4 days under the car with simple green and a garbage bag full of rags), And finally on Sunday I made it to the engine compartment to start going over it with a fine tooth comb looking for vacume leaks or anything loose. The car has the emission equipment removed and there are a few lines with screws in the ends of them( I should have known that was coming) and a few that Im not sure where they originally went, like the two in the drivers side rear wheel housing. Those two are just hanging there with custom screws in the ends. I have tightened all other lines on the motor that I have seen so far,and there were a couple loose ones, but not knowing what all was removed with the emission equipment makes tracking down what could be causing problems a little harder. Thank you for the suggestions Mark, after I get the car back to where I can start it again I will let all of you who have been helping me know if it all works. There have been many hands in this motor compartment so trying to figure out who did what and why is a big job for me being this is my first Porsche. This is a great community to be a part of and I am thankful of the knowledge I am gaining about these cars from all of you. I will keep everyone posted. Thanks again, Ben.

nathanUK '81 930 G50

At first the engine bays of these cars seem very complicated. The more time you spend on these boards & stripping down the car the less complicated they become.

Most of the stuff in the first picture will not be going back on my car.

srf506

Okay, working w/o a net here, but if one is about a 1/2' in diameter and the other about an 1/8, they're probably the oil tank vent line and the charcoal cannister vent line that comes off of a round "can" in front of the oil tank on the passenger's side. They usually attach to the airbox in order to pull the fumes back into the combustion chamber and burn them off. On the driver's side you might have another approx 1/2" size line coming up through the engine tins from an area near the turbo. Its a vent for the turbo's oil sump that also usually goes to the airbox. Do you have a non-stock airfilter and or airbox on your car? If not, you should be able to see where these hoses go on it. If you can take some digital photos and post them this forum will be more than able to help you I'm sure. From your description that's my best guess and assumption. Nothing I've mentioned so far would cause the problem you're experiencing as they are just vent lines for containing emissions.

Good luck and keep us posted,
Jim P.

Benjemin Bale

Nathen uk thats the kind of stuff I like yo see!, I havent gotten that far yet but at times I felt as though I might emerge through the glove box. Srf506 those are exactly the lines Im talking about, and both are capped off, I dont think either are turbo lines but I could be wrong. Im about to find out though because the new headers just arrived today and Im itchen to mount those up, any helpful tips on that subject would be greatly appreciated also. ( Six way adjustable wrist included), any how that still brings me back to the idle delima. As I said before the car isnt running (still waiting on ic o-ring),should be here today or thurs as soon as I get that I will put the car back to working order and check for all the suggestions, I did however find a fitting directly under the fuel head in the case , brass fitting with two black plastic lines comming out of it in the shape of a V with nothing hooked up to either plastic fitting. Can any one identify? I was thinking of putting on caps, they are very small but could be causing a problem. I will try to post pics asap in cars current condition. Thanks again, Ben