Slow idle upon cold start

[Porsche9]

I have an interesting cold start idle issue. Basically when I start the engine and it's cold it will idle at about 500 RPMs and when you hit the gas it stalls. Go to start it again and it fires right up and idles at about 1,000 and all is fine. This issue is repeatable pretty much at every cold start. Any ideas what can cause this issue.?

[Porsche9]

Anyone have an idea on what is causing this issue?

[Gelbster]

Do you touch the gas pedal before you turn the key when you start from cold ?
If you cycle the ignition switch twice before trying to start, does that make a difference ?
Stalling when you hit the gas suggests it is getting insufficient fuel/too much air. Dirty MAF ?
But why speculate? What does Herr Durametric say? Any MIL or code?

[lkchris]

Any gasoline engine requires a bit richer mixture to run when first started cold. Along with this it requires a little more throttle than is normal for warm idle.

A vacuum leak will undo this.

But, most cars of this era feature something called the idle control valve, whose purpose is to bypass some air around the maf to create extra idle speed. Mixture is richened electronically based on a temperature sensor.

So ...
Vacuum leak
Idle control valve
Temperature sensor

Fwiw but not applicable here, the advent of direct gasoline injection may eliminate the need for these components. Problem is mixture adhering to cold intake manifold and not making it to combustion chamber ... that's why engines require "choke." Mixture obviously doesn't pass through intake manifold with direct injection. "Intake manifold" describes anything behind the intake valve ... including spraying on to it from the back side.

[Porsche9]

Originally Posted by Gelbster

Do you touch the gas pedal before you turn the key when you start from cold ?
If you cycle the ignition switch twice before trying to start, does that make a difference ?
Stalling when you hit the gas suggests it is getting insufficient fuel/too much air. Dirty MAF ?
But why speculate? What does Herr Durametric say? Any MIL or code?

Never touch the gas pedal before turning the key. Tonight when I gave it a start the engine fired right up and idle at about 1000 rpm. Odd that it didn't do the usual slow idle. I don't have a durametric so I can't check. It means a trip to the shop.

[Porsche9]

Originally Posted by lkchris

Any gasoline engine requires a bit richer mixture to run when first started cold. Along with this it requires a little more throttle than is normal for warm idle.

A vacuum leak will undo this.

But, most cars of this era feature something called the idle control valve, whose purpose is to bypass some air around the maf to create extra idle speed. Mixture is richened electronically based on a temperature sensor.

So ...
Vacuum leak
Idle control valve
Temperature sensor

My guess is that it's one of the later two. The engine stalling and then upon restart running fine to me would rule out a vacuum leak as that would not go away upon restart. It didn't do it at all tonight some it looks to be intermittent.

[Smallblock454]

Hello,

sounds like it is running too lean.

I suspect a dying MAF.

If it would be a vacuum leak, it would be a permanent problem.

It's a 2002. So the thottle is electronically controlled by the the ECU. Can't imagine there is something wrong with that this way.

Low fuel pressure could cause the problem. But that would also be a more permanent problem.

Regards, Markus

[Porsche9]

Markus,

MAF is definitely another possibility. I need to either get myself a Durametric to read any error codes or simple bring it to my local Porsche shop.

Thanks!