Engine noise after shut-off

I get this prolong engine idling for a second or two after i've already turned off the car. Do you guys experience this? It sounds like the car doesn't want to shut down for that split second even though i've turned the key.. With all my other vehicles,when I turn it off, it's off no hesitation. With the p-car it almost sounds like the car is choking.. Could it be a weak battery? thanks in advance

I don't get this. Totally WAG here but perhaps your mixture is over-rich - have you checked the spark plugs to see if they are blackend?

I had a similar thing on my 993 but I think it was more the ignition switch. I think it didnt "disconnect" when I had turned the key to the off position. When you turn the car off is the key out of the ignition and still going or is it just at the point of being in the off position and key still in? Try turning it further to the left and see if it makes a difference

This used to happen on my '72 Chevy Nova (years ago). It was "dieseling." Someone else might know the technical factors behind this. Basically, it would keep turning over -- drawing fuel into the engine and then igniting it without a spark from the plugs through residual heat and pressure in the cylinders. I believe this is how diesel engines run -- they don't use spark plugs. I didn't think this was possible on a modern day car with fuel injection, electronic ignition, etc. Brings back memories. That car could keep running for minutes after I got out and locked the door.

bad gas, timing, both

What Gnome is refering to is "dieseling." Carbon deposits on the head or top of the cylinder heat up during engine run. When you shut the engine off, these deposits are red hot & can continue the combustion cycle albeit not very smoothly. I hope this isn't the case since this phenomenon can hurt your engine. It's very rare in newer cars, but did happen in older 60's & 70's autos. I think leaded gasoline had something to do with it but can't remember. Bad gas & off timing can contribute to this. You should have it check soon!

or a bad ignition barrel!

I have a similar problem with my 993, several people have similar problems with their 944's, some say a leaky/clogged fuel injector combined with residual heat in the engine (whether it be hot carbon deposits or the still hot spark plugs). Try a bottle of fuel system cleaner in a tank of petrol and give it a good hard run of 100miles or so, this helped my car for about a year, but recently I have been getting it again, although intermittantly. I know the cars are different, but I hope this is of some use to you. Here is my thread on the subject: https://rennlist.com/forums/showthre...ight=dieseling

Noooo, are you guys saying my car is "Christine" reincarnated?.. It doesn't run on its own for minutes at a time... It's only like a second or two.. I'll try the fuel cleaner stuff.. I heard that wasn't good for the car hmmmm. Maybe i'll have the dealer take a looksy.

No my car dosen't run for minutes either, they are fuel injected so won't do that once the DME has stopped pumping fuel, unless you have a leaky injector or something. Steve Wiener one of the Rennlist specialists suggested the fuel system cleaner to me, so it can't be that bad.

I'll try that... you mean fuel injector cleaner? Any suggestions as to which brand?

Muligan, As I said, there can be a short in the ignition barrel so even if you have turned the key anti clockwise all the way, power is still getting through. 996 and 986 are notorious for malfunctioning ignition barrels. Ciao, Johannes E.

I guess it's time to take her in again.. at least I get a free loaner

I was recommended "ventil sauber and techron" but I don't get that in the UK so can't comment on its effectiveness. The ignition barrel could be the culprit, but I would try the additives first as a cheaper alternative, if it dosen't help work your way up the expense table, my mechanic has no idea so I am working through the possibilities starting with the cheapest option Let us know how you get on, I am having my O2 sensor changed this week to see if that helps.

To isolate whether it is in the electrical system or not, while at idle, disconnect the negative battery able and see if the car dies immediatly. If it does, look at the electrical system...if it does not (shuts down with the same problem you have now), then it is not the electrical system.

The first warning in every Bosch electronics manual I've ever read is, "Never disconnect the battery when the engine is running". Your alternator won't like it very much and I'd imagine the unstable voltage levels wouldn't be the best thing for the various control units.

Upon disconnection of the negative cable, all circuits are open and no harm can come to them. Like when you blow the main fuse.

ok, i've added the fuel cleaner and a new tank of gas.. That didn't seem to fix the problem. I'm skeptical about testing the car to see if it's an electrical problem or not by reomving the negative line on the battery.. I think i'll just take it to the shop.. So what are some causes of this engine run-on? Alternator, battery.. yadda yadda yadda..

ok, i've added the fuel cleaner and a new tank of gas.. That didn't seem to fix the problem. I'm skeptical about testing the car to see if it's an electrical problem or not by reomving the negative line on the battery.. I think i'll just take it to the shop.. What happens when you turn the key off? Does the electrical circuit all of a sudden open? Gee...I wonder what happens to the electrical circuit when the battery is disconnected????? But, if you're skeptical, take it in. It is not the discontinuation of electricity that causes any dmage, it is the sudden appearance of it that may.

You have to drive the car pretty hard for around 100 miles for the fuel system cleaner to start working and have maximum effect, have a really spirited drive on the weekend! I can usually stop the car doing it if i rev it slightly before switching the engine off (only to about 1500 rpm). It could be the electrics, give the battery thing a try too.

Well, i took her in today and as I was describing the problem to the tech advisor a technician was standing there. he said that the noise is normal and that the flywheel makes that clanking sound after the engine cuts off because of heat and poor dampening. I told them to take a look at it anyway. I had them check out the wind noise and rattle from the 2 doors as well.. keeping my fingers crossed..

Well, if it is the flywheel then you should be able to at least determine where the general location of the noise is coming from. Put you head under the car when it is shut off and see if it's coming from the flywheel area. Then open the engine lid and do the same. Keep us posted.

Is the flywheel suppose to make that rattling/clanking sound when the motor shuts off? I'm anxious to see what the dealership tells me it is..

If it does, then it is likely a bad flywheel. The rotation of the flywheel (dual Mass) would nee to be checked to see if it is within specs. It should rotate (twist) only about 1/2 inch (15 mm) to the left and 1/2 inch to the right and spring back to the start position. If it is outside this range, then it is bad.

hmm bad flywheel, do you think that's covered under warranty or is that like wear+tear?

Well, I hope you get it sorted. The noise and symptoms you describe are the same as my 993's problem, except that mine is a Tiptronic and I don't think they have a fly wheel, isn't that part of the clutch mechanism?

Just got my car back..All I can say is they did absolutely nothing.. First they said they tighten a few speaker screws on the right side (which was where the rattle was coming from) I still hear rattling from the door area.. It could be the passenger seat bc I do see it shake alot. The driver side wind noise is still present. They said they adjusted the window by moving it up and out a smudge. I still hear drastic wind noise at 40-55 mph.. Not sure if thats normal or not The rattling/clanking sound he said was from the flywheel which he said was absolutely normal. Odd thing was another c2 pulled into the garage area and as the guy shut off his engine, I didnt hear the noise I had.. So what should/can I do now, Turn up the radio and the noise will all go away? What a waste of time taking it to the dealer..I thought they get paid for warranty work?

Redduck996, I am not sure that the engine idleing after you switch off the igniton is the flywheel noise that is described, there are a couple of threads on this on the 993 board which relate to the Light Weight Flywheel that many of them fit to the cars making this noise, it dosen't sound the same, here is a link to one of the disscussions: https://rennlist.com/forums/993-forum/179036-engine-shutdown-noise.html

I also had a 72 Chevy Nova as my first car - it dieseled endlessly. Very embarressing and caused me to park it far from any watching females.

I'm not sure if it is in fact the flywheel, but the gentleman at the dealer said it was the flywheel and that it was normal. I don't think he really investigated the issue thoroughly.. I'm going to take it back again and demand for someone to look at it. I just want to know from my fellow P-car owners if this in fact is normal or do you guys hear nothing after shut off?

I too am going to take me car to an offical porsche centre next week to try and diagnose the cause of this problem. Let me us know your findings and I'll let you know if the dealer here comes up with anything useful.

Sure will.. I need to have them re-adjust the driver side window again. It's still making wind noise at 40+ mph and now its so tight that it makes a high pitch sound when I roll up and down the window.. lol those guys are really something hahah

BTW, I ran the clutch pedal IN test and the noise/clank is almost non-existent.. Its very very very slight when the clutch is IN.. It seems the harder I run the car the more clank it makes at shut down..