David0514

I've had this problem with my car idling between 0 and 3000 until the engine would die or level out at 900 rpm. There is a screw on the throttle body that faces the drivers side about the size of a nickel that has a flat head screwdriver slot (you can turn with fingers though). The car has a CIS system pre 82 or 83 (pre electronic). Well I turned this screw and got the idling rpms up to just shy of 1100, car runs great now. When I shift to neutral instead of the car dying the engine would actually go back to just below 1100 rpm's. Well as the car warmed up and I would drop into neutral, the engine would then sometimes settle back at 1100 rpms or settle at 2000 rpms. I can get the rpms back down to 1100 by just putting the car in first and releasing the clutch a bit so the engine starts to pull. What is this 2000 rpm a sign of. What is this screw I am turning? The warmup regulator is brand new. Also, this morning it was in the twenty's. How long does it take to warm up a 3.0 under normal driving?
Any suggestions, please let me know. Thanks and Happy New Years.

Bill Gregory

David,

It sounds like you are turning the idle speed or bypass screw to adjust the idle speed, which is correct. It also sounds like your deceleration valve may be going bad. When they do, the idles tend to stay on the high side. The purpose of the deceleration valve is to keep revs up during deceleration, for emissions purposes. Here's how you test for this. On the right side, back behind the a/c compressor towards the front of the engine, you'll see a round brass-colored fixture with two largish hoses entering on the left and one rubber or cloth covered hose on the right. Disconnect the rubber or cloth hose on the right and put a plug in it. Drive around. If the problem's gone, you have two choices. One, you can replace the valve (around $60), or two, like many owners, just leave it disconnected and plugged. You'll find the revs drop just fine between shifts.

Oh, and CIS went semi-electronic in 1980.

David0514

Thanks Bill. Why is this valve on the car if I can just disconnect? So if I disconnect the RPM's will go down to a reasonable number but will I then have to keep my foot on the gas when I deccelerate to keep the engine from dying. Oh yeh, 1980 thanks. Thanks again, you've helped me out before also.

Bill Gregory

David,

Sorry, I don't remember what emission in particular Porsche was try to control by limiting how quickly the revs dropped with the deceleration valve. The deceleration valve didn't have anything to do with how far the revs drop, only to artificially keep them up for a short period of time. If everything else is in working order, when the revs drop, they'll stabilize whereever your idle is set at. I believe mine was set around 950-1000 rpm. You shouldn't have to keep your foot on the gas during deceleration, either.

DohcV8

I believe that the dashpot is there to minimize the HC spike when the throttle is sharply closed and to help the Catalytic Converter have a longer life. The HC spike causes the Cat to get hotter, which isn't good for it's longevity.

Regards,

Jerry Kroeger
82 911SC Targa

Hladun1

In the previous messages I believe there is confusion between the deceleration valve (just to the left of the throttle body with three smaller hoses) and the auxiliary air valve (behind the a/c compressor at right front of the engine with two large hoses). I discussed the function of both in a posting I made Dec 29/01 titled "CIS cold surging and backfiring".

I agree that the deceleration valve would reduce HC on throttle closure and if it stays open the engine will have a high idle speed. But without the deceleration valve connected the engine may stall on throttle closure. On the other hand, the auxiliary air valve does nothing but cause trouble!

David0514

Bill, does the deceleration valve have a hose that runs to the backside of the rubber boot over the Air flow meter. If that is it, can I just plug the this hole. Also, I am not sure that it matters, but this is a 3.0 Euro. Where you said it was emissions related I thought I should throw that in. Please let me know what you think.

Thanks.

Hladun1

You asked Bill, but the answer to your question is no. The hose from the boot goes to the auxiliary air valve and not the deceleration valve. If you plug it at the boot you'll also close off your auxiliary air regulator which gives you a fast idle when the engine is cold. The fact that your engine is a Euro shouldn't matter. Since the auxiliary air valve closes the moment your engine fires and should stay closed it can hardly have much impact on emissions.