bricem13

Hello guys

I now own my C2 for around 1.5 years. After purchase, I had to renew the clutch, as car was MY 90, I decided to go for LWF from RS. So far I had some stalling issues, mainly at cold engine.

One month ago I converted my AC to r134a using Griffiths kit. Stalling got worse (car was stalling even hot). So I decided to clean the ISV today. I did it and ISV was effectively in need of a good clean. While cleaning I disconnected the battery and let the car idle for 15 minutes once the job was done. I also look at the AFM plug (refering to http://www.pcarworkshop.com/images/b...0590geolab.pdf ) and found that the protective was already removed (also I did not loop the harness along side of the plug...).

I went for a drive, first without AC and it was fine (engine was hot), then I switched AC on and stalling came back after a few minutes of drive (crying). A couple of times during shifting I saw the revs going down and suddently up (around 2500rpm), then I completed shifting. Strange.

I investigated a bit more the stalling to see really what was happening and I don't think stalling is linked to the ISV or idling of the car: in fact during shifting (when it stalls), revs drop at around 1200rpm, all lights came on, revs seem to be maintained at 1200rpm for 1 second and then they drop !!!

I tried to reproduce this behavior with the AC off but no way to stall.

I will scantool the car this week-end but your hints are more than welcome!

Thanks in advance
Brice

crg53

THIS will solve your problem. Do a search on this forum, and you will find tons of information regarding the same issue.

bricem13

Humm. I have it in minds. However it thought the AC on would raise the idle...

Basically I red a lot of topics about stalling but the way it stalls and the fact that it is only with AC concerns me

HalV

Running the AC causes more drag on the engine, so it may cause a LWF equipped car to stall when cold. However, if the car is "warmed-up" it should not stall from using the AC. You may have something else going on. I would start with "Idle Adaptation" using a scantool or Hammer and go from there.

Andy Roe

I have exactly the same problem (RS clutch and flywheel). Before I had the Aircon fixed, mine rarely stalled with the AC on. From then on, it stalls easily when I have it turned on as the revs drop too quickly for the ECU to catch it - I too have associated it with the increased drag of the compressor and have learned to just turn the AC off before I come to a junction. Not ideal I know. Some chips can get around this, but I havent seen a 100% fix yet.

swftiii

Same issue 7 years ago. Installed Steve Wong chip and 95% of the stalling was solved.

-Skip

TRAKCAR

I have the same issue.

-nick

At operating temperature, the motronic cuts the fuel completely if it senses that the throttle is shut (idle microswitch is activated) and you are above 1240rpm. In other words, when you take your foot off of the throttle between shifts or when coming to a stop. The lwf drops the revs so quickly that the fuel cut rpm needs to be higher or else you stall. The extra drag of the a/c magnifies the issue.

I believe that Steve W (911chips) uses the fuel cut settings that the stock RS uses, or some tweak of those settings. That's how he fixes the stalling issue. And by all reports he does a good job at it. That's the only way that you're going to fix this. The stock C2/C4 motronic was never meant to run with the lwf and needs tweaked to do so without stalling.

Good luck!

griffiths

Just to be sure you are not running excessive AC pressures, which would cause the ac compressor to put a heavier load on the crank pulley, check your system AC system pressures at idle and toss the numbers out to us.

bricem13

Hi

The tech put 840g of r134a, this is so far I know what is recommended by Porsche for 964 with r134a and for 993. I don't have the records of pressure and I don't believe I can get them...

griffiths

Your tech could have done everything correctly but there could be an issue.
To eliminate one suspect, high pressures, find a local Porsche friend here on the forum that has a set of gauges and toss them on and check the readings.
Have a 6 pack of Becks handy.

ManuFromParis

I have had the LWF fitted last year when I bought the car and never had any stalling issues, except when driving backward (to park for instance) when I give a little rev and assume the flywheel's inertia will help me go back a little, like most cars with big engines do, but it doesn't and stall some times.
I got used to it very soon and managed never to stall anymore.

I love the LWF on every other situations and would not go back.

BUT recently I had the AC recharged with R134 and started to use the AC, which I never did before, and stalled several times on very hot weather, like you, when shifting down or stopping at a red light.
When it happens I just lower the button to 1.5 or 2, or shut it off, and wait to be back on normal driving situation to raise it up.

I agree with posts above about the light flywheel unable to maintain the crank rotating when reving down to idle. Same pb as when trying to move a few inchs from stop.

My mecanic told me that later chips (92(?) ->) were updated as the 911chips are on this issue.

My car is 90 but stayed property of the factory until early 93 so I guess my chip have been retrofitted as many options were added on the car when marketed (air bag, cruise control, mirrors, cup wheels, R134, etc...) I have a full history for the car, but only after it left the factory, so I'm not sure what have been done during it's early 3 years...

HalV

Perhaps this is why I don't see this behavior on my '93 C2 with stock chip? Admittedly I live in MN so I rarely drive with the AC on. However, my experience has been that the only time it will stall is if the car is cold and I have an accessory on that creates drag.