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Hunting and stalling: 3.2 Carrera


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Hi ..i have been working on these beast for over 38 year ..i have to tell you, i`ve never needed any of these gizmos..i`m sure there are cool but for me not necessary to adjust 911 Carrera engine;-) but it is what it is nowadays;-))))

 

Ivan

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Ivan, when all this shyte is over and the world gets back to normal, you have to do a European Roadtrip, drive around in your Winnebago, stop off in every town and sort out all our problems!

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23 minutes ago, Type911 said:

Ivan, when all this shyte is over and the world gets back to normal, you have to do a European Roadtrip, drive around in your Winnebago, stop off in every town and sort out all our problems!

Good idea, you can park it in my drive whilst you do a top end overhaul........

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Why dont just lean the idle mixture off on the AFM until the hunting stops . If it cuts out you've gone too far. 3mm Allen key . 

It only adjust the idle mixture. Hunting at idle is usually mixtures. You can usually smell it too. 

 

DBS

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I tried that. In the end I tried all 8 positions on the switch. None of them made the slightest difference. I'm now getting rather twitchy that this might be an overfueling problem (e.g. knackered injectors) and the cost that comes with that ! Lambda is on its way though, so I'll at least have an AFR reading to go off.

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Mine were cleaned by Redtek about 3000 miles ago. 

They also flow tested them, so it's unlikely. I've pretty much eliminated the air leak possibility. That leaves AFM, vacuum leak, dodgy idle switch, or fueling problem (e.g. injectors, over-pressure, etc.)

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3 hours ago, MonkeyChap said:

I tried that. In the end I tried all 8 positions on the switch. None of them made the slightest difference. I'm now getting rather twitchy that this might be an overfueling problem (e.g. knackered injectors) and the cost that comes with that ! Lambda is on its way though, so I'll at least have an AFR reading to go off.

Are you talking about the fuel switch on the motronic DME? or the mixture screw on the Air flow meter? 

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The 8 position switch on the motronic ECU. I didn't even know there was a mixture screw on the AFM !  One more thing to tinker with. I assume it's not doing anything at idle though, as the throttle position switch will be closed ?

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4 hours ago, MonkeyChap said:

The 8 position switch on the motronic ECU. I didn't even know there was a mixture screw on the AFM !  One more thing to tinker with. I assume it's not doing anything at idle though, as the throttle position switch will be closed ?

There is 3mm Allen key . It adjust idle mixture. Under the Afm at the front as you look at it front left hand corner. 

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This is getting a bit silly now. Is this adjustment you're talking about just for the idle mixture ? Adjusting the overall mixture at idle, with no way to read Air-Fuel-Ratio sounds a bit daft to me, but what do I know. If it's going to affect the fueling map for the car across the whole rev and throttle range, I'll wait for the WB Lambda to turn up and have a proper look. 

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1 hour ago, MonkeyChap said:

This is getting a bit silly now. Is this adjustment you're talking about just for the idle mixture ? Adjusting the overall mixture at idle, with no way to read Air-Fuel-Ratio sounds a bit daft to me, but what do I know. If it's going to affect the fueling map for the car across the whole rev and throttle range, I'll wait for the WB Lambda to turn up and have a proper look. 

It only really affects idle , think Ivan mentioned this ages ago. After 2 pages of thread you find you have a mixture adjustment screw on the AFM. But it's silly and daft until you've got your AFR gauge . Bit of a dig at people offering advice.  Best you follow your own advice. Anyway good luck now you know where your idle mixture adjustment screw is . 

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Hi - it wasn't a dig - sorry if it came over that way. Looking at it now, it does look a bit salty. It was more of a comment on, as you say, 2 pages of thread and frustration with what on the surface seems to be a simple car. By the sounds of it, most people think this is a tricky one to diagnose, and the stuff on the web is pretty inconclusive. I think I tested each of the possible causes in order of most-likely / easiest to test without breaking anything else. 

The reason for me re-posting after everything I tried is that if these threads are going to be useful to anyone else in the future, knowing what worked in what order is what these things are about. I still don't know if it's the mixture, and if you can tolerate this thread getting any longer, I'll post again as I try the other things on the list. I'd planned to summarise the process at the end, just as I did with the lights and fusebox wiring diagram I posted a while back. 

Hopefully Ivan is right, and now someone's actually told me a) this adjustment screw isn't the one on the ECU (see earlier in the thread, it's the only thing that's mentioned) and b) only affects the idle fueling I can give it a go. It would have been pretty daft if I'd just gone and leaned up the mixture at idle only to go and hole a piston at WOT. Also, I don't have Ivan's ear (or aircon) for this so I'll need an AFR meter to do it (it arrives tomorrow).  

PS - I took the bypass valve off today and tested it. I also tested the old one again. As well as the shake test, and the resistance test, you can test it opening and closing with a 12v supply (I used a desktop current limiting supply - suggest you employ a fuse if you test with a battery). The centre pin is +12V the pins either side will open or close the valve as each is connected to earth. Don't connect both to earth at the same time - move your earth lead from one outer pin to the other. The valve will click open and closed. Anyway, long story short, it turns out I'd replaced a perfectly fine air bypass valve. 

Ian

 

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13 minutes ago, MonkeyChap said:

Hi - it wasn't a dig - sorry if it came over that way. Looking at it now, it does look a bit salty. It was more of a comment on, as you say, 2 pages of thread and frustration with what on the surface seems to be a simple car. By the sounds of it, most people think this is a tricky one to diagnose, and the stuff on the web is pretty inconclusive. I think I tested each of the possible causes in order of most-likely / easiest to test without breaking anything else. 

The reason for me re-posting after everything I tried is that if these threads are going to be useful to anyone else in the future, knowing what worked in what order is what these things are about. I still don't know if it's the mixture, and if you can tolerate this thread getting any longer, I'll post again as I try the other things on the list. I'd planned to summarise the process at the end, just as I did with the lights and fusebox wiring diagram I posted a while back. 

Hopefully Ivan is right, and now someone's actually told me a) this adjustment screw isn't the one on the ECU (see earlier in the thread, it's the only thing that's mentioned) and b) only affects the idle fueling I can give it a go. It would have been pretty daft if I'd just gone and leaned up the mixture at idle only to go and hole a piston at WOT. Also, I don't have Ivan's ear (or aircon) for this so I'll need an AFR meter to do it (it arrives tomorrow).  

PS - I took the bypass valve off today and tested it. I also tested the old one again. As well as the shake test, and the resistance test, you can test it opening and closing with a 12v supply (I used a desktop current limiting supply - suggest you employ a fuse if you test with a battery). The centre pin is +12V the pins either side will open or close the valve as each is connected to earth. Don't connect both to earth at the same time - move your earth lead from one outer pin to the other. The valve will click open and closed. Anyway, long story short, it turns out I'd replaced a perfectly fine air bypass valve. 

Ian

 

No worries, it's unlikely you'll hole a piston. A 3.2 Carrera has non sequential fuel injection that's why there is a damper and a FPR on the fuel rails. If you lean the idle screw off too much the car won't start. I wouldn't worry about it leaning.  The injectors bank fire so not as rich as cis but still pretty rich. It also uses the lambda so I'm you have one fitted make sure it's working or fit a code plug(available from Porsche) 

I'd suggest you try this approach , get the car warm as it is in its current setup on the stock motronic. Set the bypass idle screw IE bridge the relay at 6pm and 1pm.(this positions the icv in the mid position) Set the idle speed with the bypass screw 7mm .   Remove the bridge. 

When it's warm sit at idle and slowly lean the screw off, a quater at a time. Blip the throttle let it settle see if the hunting improves. 

 

Make a note of your adjustments so you can return to where you were should you have no success. 

DBS

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I would do as Ivan suggests,   Wind the mixture screw in fully,  then out 3 or 4 turns,  counts how many turns you initially screw it in so you can return to your baseline point if necessary.  

Screwing it out let’s more air in so weakens the mixture,    

On another note,  I replaced the oil filler cap (which has a seal in it) a few years ago and the slight hunting I had went away,   Might just have been coincidence 

Edited by strosek34
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  • 1 year later...

I’ve been watching this thread as my Supersport suffers with this as well, but not every cold start, if it does it it will hunt between 1500 rpm to below 500rpm and stall sometimes, it will also stall every time you stop for the first 5 minutes or so of driving, but after that is fine, a recent top end refresh with a new O2 sensor hasn’t improved anything, I’ve cleaned the ICV with carb cleaner and the solenoid seems fine, sprayed around for inlet air leaks and seems ok, didn’t feel the need to adjust the mix as the MOT emissions have always been good, then someone said to me how’s your petrol filler cap as it’s a sealed system, mine is a metal cap and has always spun all the way around past the tightest area, so bought a new posh billet cap and fitted it about a month ago, with about 10 cold starts since (albeit warm weather since I fitted it) it’s been fine no hunting or stalling and the car seems a lot livelier, perhaps worth a try

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  • 1 month later...

Since my last post I’ve been using the car every weekend, had many cold and warm starts and the hunting and stalling issues have disappeared over a space of about 400 miles, maybe this maybe worth looking at, the rubber seal on the fuel caps are 30 plus years old now and mine was well squashed 

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