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Engine Cuts Out when Cold


PCGB Member
Hi All,

Happy New Year and hoping we all have a great and fault free 2023. But alas, mine is starting with a niggle.

I'm after some help for my 1985 930 Turbo, it is modified, but am hoping the issue described below is more of an original type!

During the autumn, the car started to stall when cold. The car starts on the first turn of the key and fully cold, but gets harder to start the longer the engine has run / slightly warmer. The first few times I could get it started and get where I needed to be with a few embarrassing stalls along the way. Its steadily got worse. The stall is an instantaneous 'stop' rather than a a gradual stall I would normally associate with fuel starvation.

So over the last month, I have checked / tried the the following:
-checked all the vacuum hoses and replaced any of concern.
-fuel pumps are whining on ignition and when stalled. I am assuming that they are OK.
-CDI should be OK as its a newish Retrofit unit.
-new fuel pump relay
-checked the AAV with the notch showing at cold and then closed when 12v is applied after a few mins.
-WUR has just recently been rebuilt, so assuming this is not the issue.

Any ideas of where to look next? Do I need to investigate the fuel pumps any more? Could it be anything to do with the engine cut-off relay in the engine compartment?

Thanks in advance


Hi Si,
How are you getting on with your 930 issue. I have had 30 years of sealing with the CIS system on my 930 1983 and 911SC 1977.
Looks like you have made a good start on digging around. Pinching the AAV pipe when cold should drop the revs but make no difference when warm.
My alarm disabled the warm up regulator power once and the turbo ran really poorly. Take the connect off and see if it is getting power. Check the terminals for
a resistance between 20 to 30 ohms. I had some crap get through from the fuel tank getting into the regulator. Might be worth taking it off and seeing if it is clean.
A blockage here causes all sorts of issues over temperature.
Sounds as though your cold start system is working ok. The cold start valve throws plenty of fuel to get the car started for about 10 secs. The thermo switch will disable this
cold start valve when the engine starts to warm up.
Poor starting from warm (no cold start valve operation) is usually due to pressure bleeding away quickly. This can be caused by faulty fuel accumulator operation or the fuel pump valves.
A new fuel pump solved my warm starting issues on my 911SC.

A few thoughts.
911SC Tech Advisor

Hi Rich,

Many thanks for the pointers. Will be checking your suggestions and see where we get. I'm thinking I may just replace the fuel pumps anyway. No bad thing.

Cheers for now.

Hi Si,
I changed the pumps on my 930. Note that the after market ones are more noisy. It is noticeable. The Porsche OEM ones are more expensive.
I kept the old working original ones as spares. Some suppliers do quote a dBA (dB) sound level for comparison.


I come from the world of 924s but they use the same CIS injection system and I've had my fair share of 'moments' with it over the last 10 years.

After your car starts fine from cold does the idle settle down and the engine run smoothly after a few minutes and rev cleanly or is it a bit lumpy then slowly dies? during this time the AAV will be closing and the WUR pressure will be increasing so if these are out of sync its going to cause issues. Hopefully with the WUR refurb it was fully calibrated but it still depends on the system pressure which is set in the metering head and potentially stickingo-ring split so if you can get hold of a fuel pressure gauge to hook up you can see what the systemcoldhot pressures are and have a chance of knowing if its fuel or electrical issues.

Good luck!
My 3.2 Carrera used to stall when warm almost every time when pulling up at a junction or traffic lights. Air Flow Sensor was the culprit and after replacing engine behaved perfectly.
Done. Thanks all for all your pointers.

A nice new engine cut off relay from Type 911 (thanks Matthew for the excellent service) and a bit of wire tidying up and doesn't miss a beat.

Took the opportunity of the dry weather and had a good run out.

It's been a worthwhile exercise anyway as the vacuum system has a full check and a few other tidying up bits.

Roll on the summer. Happy motoring all.

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