Car won`t idle until its warm
 

Hey Pelicans, I`ve recently bought a 1975 911 that is using the stock CIS system on a 1987 3.3 turbo motor. It wont idle until its warmed up. It just stalls. When warm it runs great! The previous owner said he tried to install a new fast idle sensor (I think thats what it`s called...) but it didn`t work, so he wasn`t sure if the new part was faulty or if there was another problem. So he left is as is.

I`d like to try and fix it but not sure what to search out. Should I search for a parts diagram for an 1987 3.3 turbo motor and start trying to trouble shoot from there. Or should I be looking up info on a 1975 CIS system.

I`m a Porsche newbie and don`t know much about electronics but certainly not afraid to dig in a try and work on it. Any suggestions would be greatly appreciated.

Cheers, Chris

???
Is this on a turbo engine or a 2.7L 911 engine?

RarlyL8 - Its a 1987 3.3 Turbo motor in a 1975 911 Carrera with CIS

Sounds like a transplant to me.
Assuming so - the fuel pressures are likely out of spec - especially if using the stock 1975 system (on a 3.3 turbo motor).
I would l highly highly recommend getting 930 WUR (again assuming your car has a NA CIS system) and having it modified to be adjustable by either RarlyL8 or Brian Leask. You'll need to install AFR gauge in the exhaust and/or hook up fuel pressure gauges to tune. I used an AFR gauge. Lots of threads on adjustable WURs.

Another possibility is vacuum/boost leak.

There are surely other possibilities but those seem like most likely culprits to me.

HTH

Hi Brandon, the motor is a transplant. Its ignition is running off a TEC1 EMS and was properly tuned and running fine for years, at some point in the last couple years it started the stalling. The PO wasn`t driving it much so he wasn`t too concerned with fixing it. So I doubt its a tuning issue. Perhaps a vacuum leak somewhere but it does run great and when warmed up will idle smoothly at 600 rpm.

the way you worded it has some confused as to if the CIS is from the 75 or 87.

assuming it is the 87 CIS, was the ECU/electronics installed for the 87? O2 sensor?

sounds like he replaced the aux air regulator (AAR). all it does it let more air into the engine when it is cold, then it closes to bring the idle back down.
the first thing i would look at is the AAR. he may have replaced it but it could be stuck closed or stuck open and the PO adjusted the idle to compensate.
check for power at the plug going to the AAR. remove it and look for 12v across the 2 pins, with the key on.

the warm up regulator(WUR) could also be bad. mixture and/or control pressures could be set for when it is warm compensating for a bad WUR. that would make it run good hot and bad cold. you need fuel pressure gauges to check pressures.

check for air leaks.

The car has a Euro CIS system with larger lines, i`m not sure what yeat of car it is off.

I just googled the AAR and saw a picture, that is the item the PO said he replaced and it didn`t work. I have it sitting in my backseat now. So it is not installed at the moment. At least I know what it`s called now and can search for more info on it. I found a useful diagram too!

Thanks!

i would still check to make sure it has power and it works.
with it cold, remove one hose, turn the key on and the port inside should close.

next i would check fuel pressures and mixture setting and air leaks.

there is a screen on the input to the WUR. you could remove the line and make sure that screen is not clogged

The heater elements in the WUR and AAR are powered by the rear fuel pump relay so turning the key to on will do nothing to them unless the front and rear fuel pumps run when turning the ignition to on.

By default the fuel pumps should not get power and run until the engine is being cranked over on the starter motor and it sucks in enough air to move the air flow meter sensor plate down a little to trip the switch on the back of the air flow meter housing.

Then depending on the year of the car, four relays.. the yellow relay in back, speed relay under the drivers seat, and the front and rear fuel pump relays become grounded and operational and the factory alarm system has to be happy or removed or else nothing will happen.