I have a 97 C2s that I just purchased.The CEL came on and the fault reading was that all 6 cylinders were misfiring .The car seems to run fine.Does anybody happen to know what this might mean?It also has an extremely rough idle.Could it be the mass air flow sensor?Thanks for any and all help
Mike

 

err, I think that means no spark plugs!

 

I'm working through the same thing on my car. Do a search on this board, and you'll find lots of good info.
Here's what I found...you'll need to check one (or more) of the following...
Mass air flow
ISV - may need to be cleaned
dual distributor belt
ignition wires (maybe, but not likely for all 6 cylinders)
Non - OEM belts. If you just had them changed, that may be it.
Dual mass flywheel - may be going out. Does the car make a lot of noise when you shut it off? The computer reads from the flywheel, so if it's wobbling, the computer throws a code thinking it's a misfire.

Anyway, take it from an armchair mechanic.

 

As pointed out by the HWFMRTBD, it can indicate one, or more, of many things. You need follow-up analysis by someone who knows what they are doing. Where are you located?

 

BTW, I (e.g, my mechanic) checked/cleaned/fixed all the above except the DMF, I turned my AC on low to bump up the idle, and voila! Problem solved!

 

I am located in Monterey Calif.The car just had an alternator and new belts installed by the dealer.It had no history of CEL light ever coming on.Could the mechanic have disconnected a vacum hose or wire?It does go off,then goes back on.Most of the time the light comes on at a stop light

 

Have the belts checked first.

 

what was the actual code you got?

 

Yep, symptoms are just like my car...CEL only comes on at idle, and my car idles rough. I think your DMF is going. Sorry. But, look at it this way...that lightweight flywheel upgrade is all that much closer!!

Listen to your car when you shut it off. If it makes a lot of noise, like a jutter or clammer, that's your DMF. Since you just bought it, you may not recognize the sound. Take it to your mechanic and ask him to check if you are not sure.

Once again, armchair mechanic here...I'm going to turn off the AC today and see if the CEL comes back on. If it does, the only thing left to fix is my DMF, because we've pretty much done everything else. I'm on my original clutch at 117k miles. Car runs great, certainly no misfires. PM me and I'll let you know what happens.

 

One more item to check -- if the alternator belt slips, it will cause misfire codes. This usually happens with non-OEM belts, but it's probably worth checking.

 

mpgandco,


see if this helps.

https://rennlist.com/forums/993-forum/219118-another-p0300-random-misfire-code.html

 

SAI Secondary Air Injection, they will try to sell You a Valve Job due to worn valve guides if so. If Your car is not using oil(more than 1 qt every 600-800 miles ) most use 1 every 1500 or so DO NOT do a valve job. Send it to Laura http://www.hergesheimer.com/ in S.Cal or whoever she recommends in Your area and they will flush out the air ports and do a system test. ANyone with a PS2 (porsche SYstem tester) can do the air flow test. This should clear it up for quite sometime.

 

Flywheel reference sensor?

 

The car just passed smog with flying colors.It gave no faults for SAI.I don;t know the exact codes,but the first time it read only cylinders 3 and 4.The next time we checked it it said misfire on all 6.There were 7 faults and I don't know what the 7th one was.It is dead Quiet on shutdown.I heard there were little to no failures on 993 flywheels,compared to the 90 to 94 911's flywheel problem,where silicon leaked out.Maybe I should have kept my low mileage,mint Boxster S or even my NSX for that matter.I have owned many Porsches,356's,mid 80.s factory widebodies,and a 930.This is making me second guess my decision to own a WIDEBODY 993

 

Hi Adrienne,

Can you describe what "rough" is? I am getting random misfires and have a rough idle...the car does shudder. If the A/C is on the higher idle clears it up a bit but I still get a tiny bit of roughness. The current dianostics appear to be worn valve guides causing the valves not to seat well at idle...but my oil consumption, while high, does not indicated guides that are totally shot.

Cheers,

Mike