warm up regulator ?s on 81sc

I've got a 81SC and the thing backfires through the pop off valve in the airbox. It runs(barely) when it is just started until it is warm then it seems to run ok. I just had the trans rebuilt and was wondering if this is something that my shop could have caused or just nutty coincedence. Is this in fact a bad warm up regulator or something else. Are there ways to test this or the thermotime switch and stuff.

As always, thanks for the great advice.

Dave
1981 911sc

Dave,

I had similar symtoms with my '82 Euro SC about two years ago, it turned out to be the Auxilary Air Regulator (AAR). Often times when they go bad in the closed position you will get low or rough idle (even stalling) until the engine is warmed up, then it will run OK. If it fails in the open position you will get a very high idle that will not go down at all. You will find this lovely device located on the passenger side of the engine between the #5 and #6 intake runners. Although there are many ways to test this and others on this list should be able to help, a simple way will be to undo the hose clamp on the right side and pull off the hose, with the engine cold and plug both AAR and the hose (those little plastic feet for folding tables sold at K-Mart and others work great,cost about a dollar) and do a cold start. If the car acts the same as it has been your problem is in the AAR. It may not be bad, just have a bad connection or may be dirty. But at 19 years old the AAR is probably bad. Give it a try, should only take you about 5 minutes.

Good Luck,

Seth

Maybe they accidently left a vacuum hose disconnected, or hit one just enough so it soon came off, or cracked it (brittle hoses).
If you don't have a CIS test kit (JC Whitney for about $60). Pull the electrical plug off of the WUR, and with a multimeter, measure the resistance across the terminals on the WUR. You should get around 20 Ohms. The value isn't that important, they vary a lot, just ensure the heater isn't an open circuit. If that's good, make sure it's getting voltage to the heating element. Setup the mulimeter to read DC voltage, and connect it to the plug on the wiring harness. Start the car and you should see around 12vdc. There are obviously a lot of things that can cause your symptoms.Thats just a simple test of the WUR heater circuit. I would invest in the CIS test kit. It will allow you to troubleshoot any fuel, and control pressure problems prior to the fuel distributor.

Hope this helps,
Leon 78SC

[This message has been edited by leon (edited 08-19-2000).]