Rough idle sometimes stalls
 

Hello everyone I have a 1998 Porsche Boxster that is running rough and throwing a CEL for general misfire and misfire cylinder 4,5,6 all on bank 2. No other codes are throwing. The car seems to run fine when I am on the gas but as soon as it idles, I can feel it running rough (like it’s misfiring) and then occasionally it stalls out when idling. The rpm needle bounces between 600-800 rpm.

This forum is my last shot before I give in and drop it off at a dealership$$$$$


What I have done so far to try to fix the issue:
1. Spark plugs x6 (verified gap is correct)
2. Coil packs x6
3. Verified all coil pack connectors are secure
3. Cleaned the throttle body
4. Replaced the fuel filter
5. Replaced the MAF
6. Unplugged the MAF (recommended on other forums)

They're all on one side of the motor. You've pretty much eliminated spark as the problem. What's left is compression and air/fuel.

Check for vacuum leaks at the plenum on that side. That would effect your mixture.

Can you check your injectors? I don't know if the wiring from all three comes off of one connector, but I would start by checking electrical connections. It's a long shot that all three on one side are bad, but...

Now we get into the internals:

Porsches have "Variocams". I don't know much about them, but that could be a cause. Maybe something's up with that side.

Lastly, have you changed your oil and checked for plastic bits in the filter? If you see bits, it could be your chain guides are gone or going. Or the tensioner on that side is going bad. If either of these is your problem, it could cause slop in the timing chain and throw your valves slightly off time, screwing up your compression. If it gets bad enough you could bend some valves.

sounds like it has vacuum leak issues but that would affect all cylinders equally. You could do a vacuum test to rule that out.
My thought is that you have a possible problem related to the cam position sensor on bank 2.
Or as mentioned an issue with the Variocam adjuster on bank 2.

My 986 BOXSTER 1997 had a problem very much alike and afetr a lot of work it was a bad fuel injector that was leaking the cause of it. Good luck.

did you got it fixed?

I have the same issue with my 3.6L 911 (cylinders 4,5,6). I have change done: coils, spark plugs, 3 smoke test, evaporative valve, flush each fuel injector, Cam shaft sensor, Crank shaft Sensor, knock sensor, clean throttle body, new MAF. This is so frustrating. I will do a compression test this weekend to see the values.
sounds like the engine will come down eventually.

There is a solenoid that activates the valve for the variocam operation. Maybe the solenoid has failed. Check the electrical connection to the solenoid (wire coming out of the cam cover). You can get to the solenoid by removing the camshaft cover (this work is more advanced - make sure to set motor to TDC for the side you are working on before removal, and you will need a special cam tool to hold cams in-place). The solenoid is probably over $200 now, a little expensive for a solenoid.

Had the same symptoms after cleaning the throttle body and knocked out a vacuum hose accidentally. I can't remember where, its my independent who've managed to locate it and reconnected it. It must have been near the TB assembly.

Vacuum leak symptoms: Sort of running okay when pressing on the gas pedal but idling quite badly and staling occasionally especially when getting near and at operating temperature.

Unhelpful I understand but I thought I'd share a similar experience. Start with the easy part and rule out a damaged vacuum hose or fitting before doing anything else.

GL with getting this fixed.