Marcus

I have had the usual problem of the idle dropping too far and not being smooth for some time, along with a slight hesitation under moderate acceleration which is worse when the car is warm. The time has come for an all out assault to sort this out.

As this seems to come up a lot on the lists I would like to know what people have found to actually cure these symptoms.

Car is an '88 S with 130k. New OE ignition leads are arriving tomorrow (ouch) and other work done recently as follows:
New FPR, AFM and temp sensor
ICV cleaned
Top end checked to rule out cam timing and broken valve springs

All sugestions gratefully received as it's starting to bug me now.

Thanks,

aka 951

Thats the way they (944S) came from the factory (at least the US versions). Porsche had a difficult time getting the car to meet emissions...the byproduct of which is a poor idle, especially when components wear. The problem is described in more detail on the 944 FAQ.

951and944S

Marcus, since you've already got ignition wires coming, install them with fresh plugs, and pay attention to the under=hood insulation.
Some listers have commented that this stuff is not necessary, because later cars don't have it.
There is a technical, tip, that states
"if engine missfire is experienced to install this insulation", wire fire to the hood....!
This is more a problem on the "S"...

The insulaton also creates a seal keeping turbo heat from crossing over the heatsheild, protecting the master cylinder and clutch slave, but that's another story...

After you see that the wires weren't the problem, let car cool, disconnect auxilary air valve connector, in between cyls #2 & 3 of the intake manifold, let DME make adjustments, (idle will go up and down, then smooth out) and let engine warm.
The idle will be slightly higher at this point, drive car to verify that hesitation is improved.
If not, remove the manifold and repair broken vaccum line leading to the AAV.
You can remove airbox, MAF, and look closely at the lines from there, get a good light and your right arm in there, moving the hoses while looking for cracks..
If, you find this to be the culprit, post back and let me know, and I'll post a method I use to repair the hose, since it's like no other 944, only the 87 and 88 S, the hose is hard to find in stock...

Terry

Marcus

Thanks Terry.

The plug leads need changing as I have a bit of a spark show going on in the dark. Your comments re the insulation make sense, you don't always think about things like that when looking at the engine with the hood up.

I know it shouldn't do this as it only started when the head gasket was replaced.

Will do as you suggest this evening and let you know what I find.

Thanks,

Marcus

Have fitted the new leads today. Car feels a bit stronger due to the wires not arcing to the head, but the idle/hesitation problems are still there. Disconnecting the AAV made no difference apart from raising the idle about 100rpm.

I shall commence the hunt for vacuum leaks as soon as possible.

If you have any more pointers Terry I'd be very grateful.

Thanks,

Tabor

If I were you I would replace your cap, rotor, and plugs if you haven't already. Then I would clean out your throttle body.

Then I would move on to replacing the throttle position switch.

You may need to replace your idle control valve too (I know you cleaned your old one).

951and944S

No problem Marcus,

These specific models DO NOT have an idle control valve as per the 951 and NA engines, it's called an auxilary air valve and is slightly different in construction.

A> What procedure was followed in "degreeing" the camshafts...? (slotted cambelt gear)
This is a tedious process on these cars and must be followed to the letter for optimum performance..
B> I'd almost garauntee that you WILL find a damaged vaccum line which has a metal orfice inserted, to restrict the volume of air to the AAV. The hose makes an abrupt 180 deg. turn and the hose usually rips when removing the manifold or reinstalling.
I keep three hoses for my personal car,(new factory Porsche), if this is the problem and you can not find a supplier, I could ship you one...
You can also make a repair, by joining the hose with clamps using 50% of the orfice for each side of the connection. If you are familiar with "American money", feel at the bend for the orfice inside the hose and look for the crack to be there. The orfice is about the size of about 15 "dimes" stacked together..

Keep me posted..!

LL

Hi
I had a same kind of problem with my -86 951. The idle was fine when the engine was cold, when warm, rpm`s dropped to 600-800. I changed the idle stabilizer which I knew was faulty from previous symptoms (knocking on it had positive effect on idle stability when engine was cold) but it didn`t cure the idle problem when the engine was warm. Then I changed the TPS (throttle position sensor) and voilà, car idles smoothly. It seems (so I`ve heard) that this part is due to a failure sooner or later and it is fairly cheap and very easy to change so I wouldn`t start looking at the idle stabilizer first (pain in the *** to change, have to remove the intake manifold at least in 951). Search previous messages in this board, there`s info how this TPS works and even though you hear the clicking sound it doesn`t mean it`s okay...mine wasn`t.

newkie

Hmm.. Interesting, as this is about the only thing i haven't changed on my car in prusuit of this problem. Enginge is totaly rebuilt and no sensor has seen 500 miles :P. Problem is still there. Had a complete MAF-system. Changed it to rogue so i could get loging Still have not figured it out. Perhaps i should look at this..