964 stalls out, relay?

[E Ride]

My 91 964 will start and run but won't stay idling, the engines idle fluctuates up and down. If I drive it it will go but then dies out, then picks up again and goes. According to my Bentlley manual they say it could be a fuel pump relay. Anybody else have any suggestions or similar experience. Thanks.....

I followed a lot of suggestions listed below and some given to me by a local Porsche shop. After putting in a new battery, r41 relay, fuel filter, and cleaning the air filter (K&N) isv valve and flap valve. I drove the car around yesterday 2-6-07 and after a few miles it ran great with no check engine light. Started it up this morning and I was back to when the check engine light flashes on at any RPM, the motor dies out and comes back on when the light goes out. The light doesn't stay on it just flashes on and off intermittently real fast and sometimes quits for a few minutes. It idles just fine until the light flashes on then kills the motor. Any other suggestions, engine temp sensor, fuel pump etc...
HELP HELP HELP !!!!



After listening and watching the check engine light has something to do with the stalling out. When the light goes on it looses power for the 1-2 seconds the check light is on, when the light then clicks off it revs back up. I can hear a relay or something clicking on in the engine compartment when the light goes on and off. It appears to be close to the throttle linkage area. Thanks for the suggestions, keep them coming.......

[kang]

Clogged fuel filter?

[AFJuvat]

Try disconnecting one of your ignition coils.

If it still does not run correctly, reconnect and disconnect the other one.

1 bad coil can cause all sorts of strange running problems.

An easy way to do this is if you look behind the coils (i.e. more towards the front of the car) you will see two ignition modules. By removing the connector from the module, you turn off a coil.

AFJ

[E Ride]

It kind of acts like is starving for fuel, but then all of a sudden will rev back up. Another thing that happens is that check engine light comes on when it looses its power, when the light goes off the engine revs up again. I don't know that the light is coming on because of the lack of fuel. Thanks....

[Jeff Alton]

Could be a faulty ISV as well.

Cheers

[colo964]

Try unplugging the O2 sensor. Also, make sure the idle microswitch gets pressed when the throttle cable is slack.

[bigchillcar]

mine cranks fine and dies if i don't hold a little gas (1990). but it's been rather cold lately..once i drive it for a couple of blocks it never stalls.

[LPDandrea]

Probably no one will beleive this, but try cleaning your battery terminals. I have to clean my ground connection about every two months. Guess how I know when to clean it. That's right, when it starts hunting at idle and stalls when big electrical draws come on like the rear heater blower. There is never any visible corrosion on the terminal. I'm wondering if there is/was a coating on the terminal clamp that has gone away or something. I figured this out when I disconnected my battery to do some electrical work and the problem went away - for a while.

I'll replace mine soon and see if that is a permanent solution.

Any body have any theories about what is happening?

[bazar01]

That is true.
I experienced the same idle fluctuations before taking out the battery..
When I took the battery out for some oil leak repairs last year, and put it back in, the idle fluctuations disappeared.
Of course, I cleaned the battery terminals and clamps.
Idle has been very stable since then.

[bigchillcar]

well, i'll certainly try this one today. i'm trying everything to clear a couple warning codes without taking the car into a shop, but nothing's worked so far. i was gonna try disconnecting both cables and hold 'em together a while..supposedly works on some cars. i'll clean 'em at the same time and report if i notice a difference.
ryan

[Pingo]

Had the same issues with my 1990 C2. Cleaned the ISV and the MAF/barndoor and wholaa, problem fixed.

[bigchillcar]

ditto, cleaned the isv last night with carb cleaner..cranks on first try now (instead of 2nd or 3rd) and idle is more 'stable'.. will clean the maf/barndoor myself as soon as i figure out where it is on this car..lol.
ryan

[FRED/LI]

Sounds all too much like my '90 a few years ago. Do you have a gauge full of warning lights going off too?

The clicking you hear is the resonance flapper being turned on and off. Your car is effectively shutting itself off and then recognizing the fault and the brain restores power.

Long story short....replaced all sorts of items....then my wrench diagnosed the ECU as being the culprit. Sent it to Otto's, they benchtested it, confirmed it as being at fault and rebuilt it. They also cautioned that the plug wires probably fried it and even sent it back with a note "Change your plug wires!"

Did so and all was well. Still is as a friend now has the car and it's his joy.

So see if you can swap a brain with a friendly temporary donor. May save you lots of time if it is indeed the problem. Good hunting.

[cwus]

I have a possibly related problem. My 89 C4 intermittently cuts out, usually does not die, but idles poorly. It sometimes clears itself, and sometimes I can clear it by hitting the throttle several times. I have replaced the DME relay, and the local dealer has had the car 3 times, without finding the problem. It will not act up for them. I happens as seldom as once/month, and as oftem as once/day, for the past 6 months.

I do not get any warning lights, unless the car stalls, which usually does not happen.

wiring problem?

fuel pump?

I will let you know if I find the cause, anyway, good luck!

[RSlater]

Originally posted by colo964
Try unplugging the O2 sensor. Also, make sure the idle microswitch gets pressed when the throttle cable is slack.

+1 on the microswitch
mine used have similar issues took to JW and he adjusted the microswitch, took all of about 5 minutes.

[bigchillcar]

well, i thought that cleaning the isv had solved my rough 'cold idle' condition, but i guess not. still dies on the first try (without touching gas), but will start on the 2nd or 3rd try. after a little warm up driving, it seems to idle fine around 900 rpm. is this typical? anything else for us rough idlin' 964 guys to try?

[cwus]

To the advice on the Oxygen sensor, thanks, but the dealer said it is ok.

I followed up on two other posts.

1. I cleaned my battery terminals, especially the smaller red wire attached to the plus terminal, and the battery posts, of course. There was some corrosion.

2. i did not know how to adjust the microswitch, but noticed that the accelerator cable had lots of slack. I tightened up the slack adjustment so there is very lilttle slack, noting that the microswitch still functions at idle.

I have not had a repeat of the problem in several days.

Not sure if permanently cured, or which one made a difference, but.........

[Richard Curtis]

CWUS: In addition to cleaning the battery posts, also clean the cable ends AND -- this is very important -- the connection where the negative cable attaches to the body. Clean that end of the cable and the body connection.