zebmaccahan

Hi all,
I've been struggling with a problem on my 997 gen2 -09 Carrera. It runs really unsmoothly at rpm 1500-2500. Some days are worse and some days better. The mechanics that have been working with the car has tried a lot, example change spark plugs and coil, updated PDK software and reprogrammed engine. So far nothing is better, it's getting worse. The big puzzle is why the mechanics can't find any OBD codes.

The car runs ok at high revs and high load, no problem there.

It seems as it is hard to locate the problem. Some say it is the PDK clutches and some says it is the engine.

Some advice, please!

extanker

a shop with better mechanics and test equipment

millertimefl

Does your idle rpm dance around a bit? I had a similar issue and it ended up being bad throttle body. Dealership tested everything and finally listen to me and swapped out TB and all is good. 2010c4s

zebmaccahan

Thank you millertimefl!

I'll ask them to look into the TB. I cannot say that it runs very bad at idle, but the rpm might dance... Where you also not having any indication on the dashboard or OBD?

millertimefl

I had no CEL or codes like you. There was some strange play in the servo mechanism of the throttle body. My idle bounced around alot and that same inconsistency in throttle position followed the rpms up to about 4k. The dealer tested everything and even flashed the Ecu. Luckily they were doing a engine tear down in the next bay and threw that TB on my car and everything was perfect. It is a tough call though...you don't want to just start spending money on parts on a hunch or my experience. Good luck!

RollingArt

How many miles on your car? Sounds like A classic case of DFI carbon buildup. Doesn't seem like a huge problem on the Gen 2 cars but I do know a 997.2 owner who's car is at the dealership right now having his engine decarbonized.

Or maybe the throttlebody like Millertime suggested.

zebmaccahan

Thanks for all the input!

Actually my mechanic was also into carbon build-up, he even showed me the inlet and there was a lot of "guck" there, especially on cylinder 6. They have now cleaned both right and left banks, new air-filter, but no improvement...

They've measured the cylinder with overpressure and found some leakage on cylinder 6, but not enough to suspect it to be the problem.

They don't Think it's the throttlebody since it sounds and looks like it is one cylinder or maybe the right cylinderbank. If it is the throttlebody, it would misfire on every cylinder, right?

millertimefl

My throttle body issue caused no misfires at all. It just caused an erratic idle and a lumpy throttle up to about 4k RPMs because the servo moving the intake flap had some play in it so it would shake/move and allow different amounts of air in causing the whole system to react. I would say I never really felt like it was a true misfire...just like the throttle had a mind of its own. Most misfires will throw a CEL or store some code.

zebmaccahan

Ok, guys here's an update!

Apparently the problem was related to a injector. Workshop have now changed the faulty injector which was located since there was some extra wearing on the cylinder wall. Compression was still ok but some extra scratches made it suspicious. Probably the injector didn't close as it should and dripped fuel, causing it to misfire on low rpm, whereas it wasn't noticeable on high revs.

When looking back on the symptoms, one could have suspected that the engine ran fat since there was excess of carbon layers on the exhaust pipes.

Thank you for all the advices and recommendations! Apparently my Porsche-dealer never heard of an injector needed to be changed, which probably also made it hard to locate the problem. Hopefully this thread can help others.

gasongasoff

Glad that worked out!