2 911 SC issues, cold start idle and switch

mikeferg75 · mikeferg75's Garage

New to me 911 SC 1980, Issues I'm having is no cold idle, will start and run easy enough with me keeping the revs at 1500 or better, but won't idle until I warm it up for a minute or 2. System Pressure's checked out ok. I've also checked the AAR and it's open cold and closed warm. I have not yet checked the the CSV or the any of the wiring from the Thermo Time Swtich? Once warm car idles perfect, CO measure is correct ect. What should I look at next?

Second issue is ignition switch, I replaced my switch first day because it was getting up, Found out somebody had been in there before and it's actually a 964 switch, now with new switch, I have had one instance where both the stater and the car would not shut off! Even took the key completely out! Once started I can also move the key one position backwards and car still runs.

I've done some searching this here this am, any input?

Bob Kontak · Bob Kontak's Garage

If it starts, pass review on the thermo-time and CSV.. It is working.

Is it a US car? Meaning does it have an O2 sensor? How did you check the CO?

There are four places air can bypass the throttle by design Idle air bypass, AAR, AAV and decel valve. With vacuum leaks, car usually runs better when rich (cold) and then as the WUR leans it out it will not be as happy.

How does it smell when cold?

mikeferg75 · mikeferg75's Garage

02 sensor is hooked up and working, CO and fuel pressure were checked at my buddys shop, we checked the CO using his sniffer so it would pass our emissions, and yes, US car.

psalt · 12-03-2011, 11:56 AM

Mike,

With the engine hot at idle, remove and plug the grey braided vacuum retard line at the back of the distributor. Reset the idle speed to 950 rpm with your fingers on the large screw at the throttle body. This alone may solve your problem. If not, test for vacuum leaks at the injectors and boots with propane or carb cleaner. Repair any vacuum leaks. Hook up an analog dwell meter to the lambda test connector and adjust the mixture to 30-40 dwell with an allen wrench. If everything is working as designed , your car should fire on the first crank. settle into a 1500-2000 rpm cold idle and drop down to 950 after a few minutes warm up driving.

If the starter runs with the key in the ON position, check the A/C relay in the smugglers box. Research the starter and fuel pump circuits on the wiring diagram. They are complex and confusing because they include the A/C, alarm, rev limiter, air flow sensor switch and are often hacked by PO's that don't understand that Porsche saved $.12 in wiring and created several bizarre failure modes.

Bob Kontak · Bob Kontak's Garage

Thanks Paul.

Paul suggested I do the disconnect trick a while back and it makes a favorable difference in helping the car start as described in his post. It is probably masking a few little issues but I am happy. Note the car will start a little differently in varying temperatures but will still follow the pattern.

56 nomad · 56 nomad's Garage

Quote:

Originally Posted by psalt

Mike,

With the engine hot at idle, remove and plug the grey braided vacuum retard line at the back of the distributor. Reset the idle speed to 950 rpm with your fingers on the large screw at the throttle body. This alone may solve your problem. If not, test for vacuum leaks at the injectors and boots with propane or carb cleaner. Repair any vacuum leaks. Hook up an analog dwell meter to the lambda test connector and adjust the mixture to 30-40 dwell with an allen wrench. If everything is working as designed , your car should fire on the first crank. settle into a 1500-2000 rpm cold idle and drop down to 950 after a few minutes warm up driving.

If the starter runs with the key in the ON position, check the A/C relay in the smugglers box. Research the starter and fuel pump circuits on the wiring diagram. They are complex and confusing because they include the A/C, alarm, rev limiter, air flow sensor switch and are often hacked by PO's that don't understand that Porsche saved $.12 in wiring and created several bizarre failure modes.

paul , how do you check this...cann you direct me to a source on the net that has some photos? thanks , ben

psalt · 12-03-2011, 01:59 PM

Ben,

Everything you need to know should be right on this site, search for lambda CIS. The test connector is a loose wire with a black rubber cap under the plastic cover on the right side of the engine compartment. Remove the two wing nuts, cover and start fishing around. You want to hook up the dwell meter to the green/white stripe wire without touching the other two pins.

Paul