944 (86) cold idle problem

AllisterBrimble · 11-11-2000, 05:50 PM

When my 944 is cold I'm getting a very low idle (around 600) and I also have problems accelerating at low speeds, often stalling. However, once warm, the idle is steady at 900 and all is ok.

What I have noticed is that mixture seems very rich on cold start as if on heavy choke.

I have taken this problem to a porsche service garage. They said the mixture could not be set and that a new airflow meter was required before further investigation.
I've fitted another (reconditioned) airflow meter but my problems are still there.
I'm wondering whether my problem lies somewhere else ?

Any ideas ?

Thanks in advance
Allister

AllisterBrimble · 11-11-2000, 06:06 PM

Also, I've recently noticed that the idle problem is cured when you pull off the sensor pipe from one of the valves on the top right of the engine. The mixture remains too rich though. Does anyone know what this valve is ?

Dave951 · Dave951's Garage

Sounds like the auxillary air valve to me. It lies underneath the intake manifold(on my 951) and is a motor-looking thing with a couple big(~3/4") hoses on it.

Have it checked.

Dave

T86951 · 11-11-2000, 08:08 PM

check to see if you are getting vacumn to the 2 fuel pressure regulaters (one on each end on top of the fuel rail, they are round about 2 inches long and 2 inches in diameter and each has a vacumn line going into them). If you don't have vacumn there with the motor running the car will idle slow (real slow when cold) and stumble and run bad until you really get the rpm's upunder acceleration, plugs black and overrich conditin. The vacumn lines should run to a tee and go somewhere behind the trottle plate for constant vacumn. I had that problem same as you and that was it, no vacumn to the regulaters. I have told several members about it and a couple times that was their problem. I doesn't cost anything to check, with the motor running pull one of the vacumn lines off one of the regulators and touch the tip of the line with your finger to see if it has vacumn, it will be only slight cause its a tiny line.

AllisterBrimble · 11-12-2000, 08:31 AM

That would set the idle speed too high when warm (I've tried it before).

You're right about needing a better mechanic! In my last service with him, the car came back with a badly timed cam belt - the whole car was shaking (A LOT), so I really wonder how much they know about 944's. What's more, the airflow meter I removed seemed fine. They are an offical porsche service centre (UK) which is even more worrying.

Quote:

Originally posted by mideastmafia:
try adjusting your idle speed setting. It is on the throddle wheel. it is a flat head screw with a bolt at the end of it. It is also lined with yellow paint..

Actually,
you should take it to a mechanic that doesnt talk out his ass.

SHAUN

AllisterBrimble · 11-12-2000, 08:33 AM

Sounds like a possiblity. I'll check it out by pinching the hose to it whilst cold - the revs should go down according to the haynes manual.

Quote:

Originally posted by Dave951:
Sounds like the auxillary air valve to me. It lies underneath the intake manifold(on my 951) and is a motor-looking thing with a couple big(~3/4") hoses on it.

Have it checked.

Dave

AllisterBrimble · 11-12-2000, 08:34 AM

That does sound very similar to my problem. I'll check it out !

Thanks
Allister

Quote:

Originally posted by T86951:
check to see if you are getting vacumn to the 2 fuel pressure regulaters (one on each end on top of the fuel rail, they are round about 2 inches long and 2 inches in diameter and each has a vacumn line going into them). If you don't have vacumn there with the motor running the car will idle slow (real slow when cold) and stumble and run bad until you really get the rpm's upunder acceleration, plugs black and overrich conditin. The vacumn lines should run to a tee and go somewhere behind the trottle plate for constant vacumn. I had that problem same as you and that was it, no vacumn to the regulaters. I have told several members about it and a couple times that was their problem. I doesn't cost anything to check, with the motor running pull one of the vacumn lines off one of the regulators and touch the tip of the line with your finger to see if it has vacumn, it will be only slight cause its a tiny line.

AllisterBrimble · 11-12-2000, 09:20 AM

Quote:

Originally posted by T86951:
check to see if you are getting vacumn to the 2 fuel pressure regulaters (one on each end on top of the fuel rail, they are round about 2 inches long and 2 inches in diameter and each has a vacumn line going into them). If you don't have vacumn there with the motor running the car will idle slow (real slow when cold) and stumble and run bad until you really get the rpm's upunder acceleration, plugs black and overrich conditin. The vacumn lines should run to a tee and go somewhere behind the trottle plate for constant vacumn. I had that problem same as you and that was it, no vacumn to the regulaters. I have told several members about it and a couple times that was their problem. I doesn't cost anything to check, with the motor running pull one of the vacumn lines off one of the regulators and touch the tip of the line with your finger to see if it has vacumn, it will be only slight cause its a tiny line.

There's no vacuum there at all. Perhaps this is the problem. Where does this vacuum pipe come from before it reaches the pressure regulators ? Perhaps the problem is there ? (Auxilliary air valve by any chance ?)

T86951 · 11-14-2000, 05:44 AM

The vacumn lines should run to a tee and go somewhere behind the trottle plate for constant vacumn. It doesn't go to the idle valve but over on the driver side to a spot behind the the throttle body. If you don't have vacumn to the regulators it pumps your engine full of gas an bad idle rich condition. You will just have to trace the vacumn line and find the place it is loose. Not easy on a 951 due to all the plumbing but on a na 944 its right behind the thottle body on the side, easy to find, little tiny vac hose.

Dan

[This message has been edited by T86951 (edited 11-14-2000).]

AllisterBrimble · 11-14-2000, 10:57 AM

I think it's ok. There is vacuum, so the pipes are ok. There's just no suction as I would have expected (a lot of the other vacuum pipes on the car suck quite hard).

I've now tested the auxilliary air valve by pinching the pipe going to it whilst at normal operating temperture (as stated in the Haynes manual). As the revs do not go down it looks like this might be the problem.
I would have thought the pipe should be pinched when cold ?? Perhaps the Haynes manual is wrong ?

Quote:

Originally posted by T86951:
The vacumn lines should run to a tee and go somewhere behind the trottle plate for constant vacumn. It doesn't go to the idle valve but over on the driver side to a spot behind the the throttle body. If you don't have vacumn to the regulators it pumps your engine full of gas an bad idle rich condition. You will just have to trace the vacumn line and find the place it is loose. Not easy on a 951 due to all the plumbing but on a na 944 its right behind the thottle body on the side, easy to find, little tiny vac hose.

Dan

[This message has been edited by T86951 (edited 11-14-2000).]