3.2 litre wants to stall when clutched coming to a stop

[Weaver]

My 87K mile '88 3.2 litre Carrera wants to stall when we come to a stop like a stop sign or a stop light for example. I will be coming down the gears to come to a stop and I usually clutch it and take it out of second anywhere from 1700 to 2000 rpm while on the brakes. The engine will fall to 400 rpm when the cluch goes in then will rev to 1200 or 1300 rpm then settle to the idle level. Sometimes when cold it will stumble and stall. It will not do it while slowly moving forward or stop and go like when I'm in line at a stop sign or a roundabout, just when coming down from constant driving. Does this sound fimilar to anyone?

Here is a list of relavent mods and repairs:
SteveW chip 93 octane for SSIs
SSIs
new braided fuel line from rails to "t"
fuel filter 4K miles ago
new o2 sensor 4K miles ago
new cylinder head temp sensor 6k miles ago
Magnacor 8mm plug leads
valve adjustment this winter
new plugs
new air filter

Thank you for your time

[john walker's workshop]

SW chips sometimes don't allow the idle stabilizer valve to function properly. you could try cleaning it with spray carb cleaner. a customer recently sent his back for reprogramming and it worked after that. be sure the throttle closed micro-switch is getting tripped.

[crobinson]

I guess there could be a bunch of things that could do this that are DME control related. One simple thing I would mention is to look at the oil filler cap seal. My 87 Targa 3.2 was having idle problems until I changed the cap. I hope there is someone that understands that, I don't! Why do you need pressure in the sump to maintain smooth idle. If I remove the cap, it will die or almost die. Sorry to ask another question.

[saintz]

I had this exact problem. A new DME relay fixed it.

[Steve W]

Nothing to do with the chip. The decel and idle should actually be significantly improved over the stock chip. Factors that will cause stalling are:

1) too low of a base idle adjustment

2) base idle mixture either too rich or too lean. Idle CO should be between 0.6-0.8% before the cat

3) intake air leaks causing mixture problems and thus mis-metering by the air flow meter

4) gummed up idle control valve

5) intermittent or non-activating idle position microswitch

6) oil and dirt accumulation around the inside of the throttle body where the throttle butterfly closes

7) ultralight flywheels or aftermarket cams such as 964 or 20/21s, in which case a different chip is needed

If the stall is not severe, increasing base idle speed by turning the screw counterclockwise 2-3 turns out may fix the problem. Otherwise, clean items 6 and 4, check item 5, check item #3 by disconnecting the O2 sensor and connector to the ICV, and spray engine starting fluid at the intake manifold gaskets, injector O-rings, manifold boots, vacuum lines, and anywhere you could suspect a intake air leak. If the RPMs rise rapidly, you have located an air leak that needs to be fixed.

Then check and address item #2, either with a CO meter at your local mechanic, or using the reading off the car's O2 sensor with a voltmeter. See: Idle Hunting -- The problem continues!!

Finally adjust item #1, by using the factory method of jumpering B and C of the test socket, and setting idle to 880 rpm. See the bottom of the following page: http://www.911chips.com/dmeconvr.htm
Properly set, on decel, the rpms should not subdip below 880 rpm and if it does, raise the base speed. Conversely, when warm, the engine should not idle above 900-925 rpm, and if so, turn down the base speed. Properly set, with my chip, you will see on decel, the rpm dropping like normal to 1050 rpm, after which, the rpms will float gently down to about 880 rpm in about a second, which gives even old worn ICVs time to catch and stabilize the idle.

[dentist90]

Originally Posted by crobinson

I guess there could be a bunch of things that could do this that are DME control related. One simple thing I would mention is to look at the oil filler cap seal. My 87 Targa 3.2 was having idle problems until I changed the cap. I hope there is someone that understands that, I don't! Why do you need pressure in the sump to maintain smooth idle. If I remove the cap, it will die or almost die. Sorry to ask another question.

The oil tank is under vacuum from the intake. This is to help purge oil vapour. Opening the oil cap, or a leaky gasket under it, allows unmetered air to enter the intake, aka: a vacuum leak.
The routing of the crankcase ventilation is quite circuitous: a vacuum hose runs to the oil tank, another hose runs from the oil tank to the crankcase breather, yet another runs from the oil tank to the back of the throttle body above the throttle plate. There are more supplementary hoses as well.

That is also why, if you overfill your oil tank, you can get massive oil smoke from your engine. Oil can spill up one of these hoses into your intake.

[Thrlls]

Thank you for your explanation Steve!

I'm experiencing almost the same symptoms, except my engine will stall only when it is cold. On another thread I was advised to shake the ICV, which I haven't gotten around to yet, but I'll try that as well as what is listed. I hope it solves the problem.

[Steve W]

If it stalls only when cold, usually it's because the idle fuel mixture if off - usually too rich. This is because the O2 sensor hasn't warmed up enough yet to trim the fuel mixture. But you don't want to be depending on the O2 sensor to correct this, as the DME is not adaptive, and you will repeatedly experience the same symptoms when the car is cold.

[Thrlls]

Originally Posted by Steve W

If it stalls only when cold, usually it's because the idle fuel mixture if off - usually too rich. This is because the O2 sensor hasn't warmed up enough yet to trim the fuel mixture. But you don't want to be depending on the O2 sensor to correct this, as the DME is not adaptive, and you will repeatedly experience the same symptoms when the car is cold.

Thanks again Steve, I'll get that checked out.

[Thrlls]

While removing the ICV, I noticed the clamps on the hoses were not tight enough. I removed the ICV shook it...it rattled, but I still cleaned it out with some throttle body cleaner, put on new clamps, tightened them down...and walla!
No more stalling.

Thank you for the help!

[300cd300sdl911]

Thrills,

I had the same symptom as you with my ICV. I also cleaned with my valve without disassembly - many folks on the board recommend taking the valve apart to clean thoroughly. Anyway, my cleaning only yielded a couple of weeks of driving before the stalling began occurring again.
I just replaced the valve - only about $143 from our host. Everything has been fine since. Just thought you should know.......

[Thrlls]

Originally Posted by 300cd300sdl911

Thrills,

I had the same symptom as you with my ICV. I also cleaned with my valve without disassembly - many folks on the board recommend taking the valve apart to clean thoroughly. Anyway, my cleaning only yielded a couple of weeks of driving before the stalling began occurring again.
I just replaced the valve - only about $143 from our host. Everything has been fine since. Just thought you should know.......

Yes, very good to know...Thank You!

[john walker's workshop]

i don't mean to say that SW chips cause this. just my experience with a couple of cars that did not have ISV function worth a crap after servicing them and after removing the SW chip and reinstalling the original one, the ISV functioned correctly. kind of seems that it was the chip then, but i could be wrong. other ones with the chip worked fine. wierd.

[dentist90]

It's no wonder the ICV gums up so readily. I had my air cleaner and throttle body off just 1 year ago and look at the oily grunge that accumulates after just 5,000km:



And before you ask... NO, I did not overfill the oil tank.

[Lesworth]

Originally Posted by Steve W

Nothing to do with the chip. The decel and idle should actually be significantly improved over the stock chip. Factors that will cause stalling are:

2) base idle mixture either too rich or too lean. Idle CO should be between 0.6-0.8% before the cat

Then check and address item #2, either with a CO meter at your local mechanic, or using the reading off the car's O2 sensor with a voltmeter. See: Idle Hunting -- The problem continues!!

Regarding this possible cause, my car (which has this symptoms) runs at around 2% CO even with the bypass screw on the AFM dialled as lean as you can get without the screw falling out. Not sure what the answer to this is yet...

Weaver: Did you get to the bottom of your issue?

[wolf]

imho pretty normal for a cold 3.2 to stall. if i drive 500 meters in winter and stop it sometimes stalls. never with a warm engine. seldom in summer.

[Steve W]

A CO of 2% at idle, especially with the idle mixture screw all the way out indicates something is wrong with the car causing it to run rich. The rich mixture will cause subdipping and stalling on decel. Typically the idle mixture screw is only about 1.5 to 3 turns out from fully closed on a engine in good condition. A rich mixture can be due to:

1) leaking or bad vacuum lines to the fuel pressure regulator and/or fuel damper

2) bad fuel pressure regulator - stock fuel pressure should be about 38-40 psi with the vacuum line disconnected

3) bad head temp sensor (check specs)

4) leaking fuel injector not closing properly

5) fuel quality switch in DME not in full counterclockwise position

6) Air flow meter (AFM) out of calibration

7) bad O2 sensor or connector

Recently on a 85 Carrera, we diagnosed a rich running condition that caused a failed smog test even having been worked at two top Porsche shops here in L.A. First was a improperly calibrated and worn AFM were the pointer was advanced internally. See post:you asked and you shall receive Premuffler goodness




Second, we found a bad crimp connection at the O2 sensor connector. The factory O2 connector off the car had disintegrated so the owner had crimped a new bullet connector on the wiring. Mulitmeter tests showed the connector OHM'd out ok at 0.8 ohm from the connector to the DME plug, but a LM-1 meter showed the AFRs were still not being modulated properly by the O2 sensor. Tried a new O2 sensor and same thing. I soldered the crimped bullet, resistance dropped to 0.1 ohm, and instantly the O2 sensor worked. Owner passed smog no problem the next day.

[Lesworth]

Thanks Steve.

I had the AFM sent away to be refurbished and all the settings checked against the factory settings and the Company say all was ok.

I did swap it out with a known working AFM. The car started but the revs immediately started to fluctuate up and down the rev range and at one point stalled so I dont know if this was inconclusive or is actually telling me something!

I also had the injectors flow tested and re-furbed with new 'o' rings fitted. CHT sensor seems ok too as its the later two wire type and the basic checks I performed with a mulimetre seemed to show this working ok. I'll look inot the vac lines for the pressure regulator. FQS switch is also set correctly.

I am leaning towards the AFM still not being right at the moment and am at the point where I'm going to give the car to someone who knows what they are doing to check all this properly.

[glennspiegler]

I am working up the same problem. After removing and cleaning the ICV valve, the rattle with rotation is present (can see the valve move freely), the Bentley manual says to connect the plug with the ignition on and the valve should close half way. Mine does but oscillates a few millimeters back and forth. Is this normal?

[Lesworth]

Rubber elbow on the fuel pressure damper seems to be poorly fitting and even may be too large as the platic tube just popped out when I touched it. I replaced the rubber so now have a much better fit but the problem still remains altough may be a little worse. I obviously didnt expect it to be fin as the mixture and idle will need to be reset properly with a gas analyser. I will also have the fule pressure tested properly at the same time. More tome come in a few weeks...