944 S idles fast once engine is warm

[Gatornapper]

Engine starts & idles fine when cold, but once it is up to operating temp, idle moves up to 1300 - 1350 rpm.

Clark's Garage has how to on setting idle, but where is Diagnostic Plug?

Idle Speed Adjustment

Knowledgeable 944 guy said it was likely Air Control Valve.

Never worked on L-Jetronic before - learning. Is there a good book on it? Just learned CIS on my '80 924 Turbo I restored & sold......

GN

[rhett]

Hi - I also had the same problem. Clarks does state 'The 944S and S2 models use a system called "adaptive idle speed volumetric efficiency regulation" and do not require idle speed adjustment.' - so there is really nothing you can easily adjust on the 16V models. What I found was a small vac leak, but also cleaned the idle control valve (under the inlet manifold) and the problem went away. The rubber tubes and pipes that make up the complicated air/vac system on the 944S are going to be pretty tired by now, and small cracks will occur through age, giving rise to leaks. So a really good check of all of them might lead you to a culprit!

Unfortunately, to get to all the pipes and the valve, you really do need to take the inlet manifold off, so the fuel rail, injectors, regulators, AFM and other associated stuff all has to come off - be prepared... I have heard that a smoke test can pinpoint leaks, but I have never done that - however, there are plenty of guys on this forum who have chased vac leaks and have a wealth of knowledge - perhaps they might chip in..?

Hope that helps - good luck...Rhett.

[Gatornapper]

Rhett -

Thanks! I did find one vac leak and thought that would surely fix the problem - but it did not to my surprise. A major hose had broken.

DO NOT LIKE having to pull intake manifold & fuel rail to get to the idle control valve to test it.

So I'll start looking for another vacuum leak first. I had a 924 Turbo that also had miles of critical vacuum lines & know well what you speak of.

The lines on this car look like new - quite unlike the lines on my '80 931 with only 60k miles on it. But they still have 150k miles on them and 35 years.

Thanks again,

GN

Originally Posted by rhett

Hi - I also had the same problem. Clarks does state 'The 944S and S2 models use a system called "adaptive idle speed volumetric efficiency regulation" and do not require idle speed adjustment.' - so there is really nothing you can easily adjust on the 16V models. What I found was a small vac leak, but also cleaned the idle control valve (under the inlet manifold) and the problem went away. The rubber tubes and pipes that make up the complicated air/vac system on the 944S are going to be pretty tired by now, and small cracks will occur through age, giving rise to leaks. So a really good check of all of them might lead you to a culprit!

Unfortunately, to get to all the pipes and the valve, you really do need to take the inlet manifold off, so the fuel rail, injectors, regulators, AFM and other associated stuff all has to come off - be prepared... I have heard that a smoke test can pinpoint leaks, but I have never done that - however, there are plenty of guys on this forum who have chased vac leaks and have a wealth of knowledge - perhaps they might chip in..?

Hope that helps - good luck...Rhett.

[Monkey Wrench]

there is a trick with a propane torch, don't light it set it on full and go around pointing it near to hoses etc. if you have a leak the theory is it will take in propane and you'll hear the idle speed change. for safety reasons it might not be recommended but I think with reasonable caution and a door open, soe cross ventilation, you can do this fairly safely, of course dont let the raw propane collect as there is potential there for fire or explosion. whether it will show anything , maybe, maybe not but anyway, for what it's worth.

another trick is to grab a piece of clean 1/4" plastic hose. stick one end in your ear, stick the other end near-to things, the theory is then you may hear the hiss where it were normally covered by other noise.

which hoses to suspect is a better question for the others..

[djnolan]

Make sure the throttle position sensor is not loose or out of adjustment. Make sure throttle plate is clean and not sticking.

[Gatornapper]

Monkey Wrench & djnolan - thanks for the tips. Well appreciated.

Sure would love to get this book:

https://www.amazon.com/Gasoline-Fuel-Injection-System-L-Jetronic-Instruction/dp/0837604702/ref=sr_1_1?crid=23N8FYZ027EGQ&keywords=l-jetronic+fuel+injection&qid=1665225183&qu=eyJxc2MiOiIyLjIwIiwicXNhIjoiMC4wMCIsInFzcCI6IjA uMDAifQ%3D%3D&s=books&sprefix=l-jetronic+fuel+injection%2Cstripbooks%2C148&sr=1-1

But none out there.

GN

[Gatornapper]

Gonna run a can or two of good Fuel Injector Cleaner in the air intake while modulating the throttle plate.......

Gonna try to find intake point for the idle control valve (atmosphere side of valve) and see if I can inject FI Cleaner in there too... if valve is stuck, that might free it up.

GN

[djnolan]

this one cover Motronic

https://www.amazon.com/Gasoline-Engine-Management-Technical-Instruction/dp/0837611008/ref=sr_1_2?crid=X3OUGJX4YUSR&keywords=bosch+motronic&qid=1665229938&qu=eyJxc2MiOiIxLjQzIiwicXNhIjoiMC4wMCIsInFzcCI6IjA uMDAifQ%3D%3D&s=books&sprefix=bosch+motronic%2Cstripbooks%2C99&sr=1-2

One available for $679. Is it on ebook?

[944 Ecology]

It is not L Jetronic... It is DME... (Digital Motor Electronics) or Motronic ... completely different animal.

[Gatornapper]

George -

Many thanks for the correction! I'm in kindergarden when it comes to this engine - a whole new animal to me - and a wonderful one as I've been hearing for years......

GN

Originally Posted by 944 Ecology

It is not L Jetronic... It is DME... (Digital Motor Electronics) or Motronic ... completely different animal.

[Gatornapper]

Guys -

According to this diagram, the input feed to the Idle Speed Control Valve (lower right corner) is in the Intake Tube just past the Air Flow Meter.

This being the case, a simple test should tell me whether the valve is the source of the increased idle speed when engine is hot.......If I plug intake line to the ISCV with engine hot and idling, and the ISCV is the problem, the idle speed should drop to 900 rpm when I plug the line. I'll of course also plug the line connection into the Intake Tube.

Correct? You all agree?

GN

[Gatornapper]

Also, if valve is the problem, it could just be stuck and some injector cleaner in the line (it would be stuck open) might clean it and unstick it.

GN

[Gatornapper]

Weird. Had occasions today when after running on highway for 10 or so miles, stopped, and engine idled perfectly about 950 rpm.

But only occasions. Most of the time idles at 1,350 or so.

Why would it sometimes be correct if Idle Control Valve is the problem?

GN

[Jfrahm]

You can pull out and clean or replace the ISV. This would also be a time to check for damage to the related large vacuum hoses. Something that cuts through crud like Seafoam or Berryman B12 is good. Obviously you mainly want to soak the valve area and not the electrical part.

The ISV for a Saab, Volvo or BMW can also fit and work, even if the hose arrangement is different. You do need to match the pin count in the connector, 2 vs. 3. My 1994 968 came to me with a BMW E30 ISV in it, which worked fine (I replaced it anyway with a correct part).

[dme]

verify that the idle switch on the TPS is working. My TPS would click when the throttle was closed, but it wasn't really working. I chased this problem far too long.

[Gatornapper]

Sure don't want to do this unless I have to as it entails pulling the whole intake manifold and intake tube, throttle body, etc.

More I drive the car it seems the more it is settling down at idle to the proper rpm......

Seems line to ISV from the intake tube is virtually inaccessible, so idea of squirting cleaner directly in it is not likely to happen......

GN

Originally Posted by Jfrahm

You can pull out and clean or replace the ISV. This would also be a time to check for damage to the related large vacuum hoses. Something that cuts through crud like Seafoam or Berryman B12 is good. Obviously you mainly want to soak the valve area and not the electrical part.

The ISV for a Saab, Volvo or BMW can also fit and work, even if the hose arrangement is different. You do need to match the pin count in the connector, 2 vs. 3. My 1994 968 came to me with a BMW E30 ISV in it, which worked fine (I replaced it anyway with a correct part).

[Gatornapper]

Dan -

Directions on how to do this?

Thanks,

GN

Originally Posted by dme

verify that the idle switch on the TPS is working. My TPS would click when the throttle was closed, but it wasn't really working. I chased this problem far too long.

[dme]

Originally Posted by Gatornapper

Dan -

Directions on how to do this?

Thanks,

GN

Clarks Garage under Electrical and Sensors. I'd check it directly at the TPS and not the DME for a quick fairly easy test.

[Gatornapper]

Thank you Dan.

GN

Originally Posted by dme

Clarks Garage under Electrical and Sensors. I'd check it directly at the TPS and not the DME for a quick fairly easy test.

[Gatornapper]

Prior to my purchase, it appears this car was not driven much. I've driven it daily since getting it and am noticing more and more that once warm, the engine is idling at an acceptable 950rpm.

Gonna use some more throttle body cleaner in running engine, hoping that some will bypass the intake tube via the ISV and that it helps clean the valve up a bit.

Not going to do anything for a while as it seems to be improving as I drive the car.

GN