idle speed too fast

[Boydskyking]

I have 1980 sc nd it idles fast. It was running lean and an I adjusted it by using the 3 mm wrench and turning the screw a quarter of turn untill you could push down on the wrench and it would not effect the engine .I then continued the turnning until the engine becane to hunt ,I then turned the wrench back until the engine ran smooth. I runs smooth and speeds up with out popping or snapping.The problem is now it idles at bout 1800 and I cant seems to slow it down. I have adjusted the air justment screw behind the air valve to no vail . Any suggustions

[Targalid]

At this point you have adjusted the fuel/air mix as best you can. This tells me you have an air leak somewhere. You need to diagnose the source of this leak. You have too much volume through the metering plate. Check all the hose connections which is not easy because many of them are hidden. I found one on the back of my airbox that had a loose clamp. When I tightened the clamp another major air leak was discovered and fixed. At that point I had to go through the fuel/air adjustment again. Just be persistent. You will find it and you will be a CIS adjustment expert by the end of it. Spraying carb cleaner or starter fluid can help to find leaks though maybe not so easy to detect at 1800 rpm.

[ossiblue]

+1 on an air leak.

You've already messed with the mixture screw which, typically, should be the last thing adjusted in dealing with CIS issues. High idle that cannot be adjusted via the bypass screw is classic air leak symptom. Follow all the suggestions mentioned above for possible locations of the leak. Best method is to do a smoke test, if possible (do a search--here's an example: Help with CIS test numbers (new guy)) to locate the leak.

Once the leak has been found and corrected, you will need to test your fuel pressures to see if they're in spec, and reset you mixture screw using a gas analyzer if at all possible.

[al lkosmal]

+2 on the vacuum leak.

Don't forget to check that your pop off valve is still bonded in and sealed and that the lid/o-ring is properly seated/sealed. (have any backfires lately?)

regards,
al

[Brett San diego]

Do you have cruise control? I had a fast idle on my 1978 911 that I couldn't solve until my father-in-law jiggled the cruise control cable. Turned out the cable was adjusted too tight and was keeping the throttle open slightly. Prior to the problem I had had the heater ducts removed and such, and I ended up re-routing the cruise control cable when I put it back together which caused it to be a little tighter.

If you don't have cruise control, I'd recommend touching the throttle linkage anyway and confirming that the throttle plate is being allowed to fully close. Manually push it to the closed position and see if the idle drops. If it does, then adjust the throttle linkage appropriately to allow the throttle to close. If the throttle isn't the problem, then look for an air leak and check that your auxiliary air regulator is closing properly when the engine warms.

I suppose your "running lean" comments also indicates that you have an air leak already, though...

Brett

[boyt911sc]

Originally Posted by Boydskyking

I have 1980 sc nd it idles fast. It was running lean and an I adjusted it by using the 3 mm wrench and turning the screw a quarter of turn untill you could push down on the wrench and it would not effect the engine .I then continued the turnning until the engine becane to hunt ,I then turned the wrench back until the engine ran smooth. I runs smooth and speeds up with out popping or snapping.The problem is now it idles at bout 1800 and I cant seems to slow it down. I have adjusted the air justment screw behind the air valve to no vail . Any suggustions

Boydskyking,

Now that you have altered the setting of the air mixture screw without verifying the absence of a vacuum/air leak makes the troubleshooting more interesting. It was lean because of less fuel or more air? Why people adjust the mixture setting without knowing the root cause of the problem still amazes me even in spite of the vast discussions about this subject.

While there are some posts about adjusting the air mixture without gauges, the author/s failed to emphasized the need to verify the vacuum/air leak side of the equation. Chances are the LEAN condition is caused by unmetered air into the system than lower fuel pressure. Or the other way around.

My only suggestion to you is test and verify. Avoid troubleshooting work that depends on guess-work and your car will run on demand. Keep us posted.

Tony

[Boydskyking]

Sorry Tony but you know I am newbie and am feeling my way on CIS . I love my car and am getting a lot of good informtion from form. So if I do things that is not quite right for you I am sorry.