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Intermittent surging & complete power loss- 996

  • 2003
  • 911 Carrera 4S
63 000

Hi all, new to the club and to Porsche ownership... first technical question.  Just purchased a nice 2003 C4S (w. X51 option)... clean PPI but would not pass emissions, seller installed new OEM-equivalent cats.  Upon delivery I had an LN Engineering IMS bearing installed as a precautionary measure... did the clutch and flywheel while in there (at Gerber Motorsports, Seattle)... at that time, engine was throwing no codes.  Three times in the space of ~300 miles the engine has exhibited idle surging and almost complete power loss... first incident as described to Gerber~2 days after IMS/clutch work:

Backed out of the garage, all felt normal... got out to close the garage door and noted smoke out of both exhausts, smelled like it was running rich... I thought: well, engine is cold, that probably accounts for the rich mixture.  I'm new to the car but I had never seen visible smoke before.


Drive 100 feet to end of driveway, feels a bit stumbly off-idle, with a lack of low-end torque... very touchy to get things moving.  Release clutch to exit driveway and it acts like it wants to stall.  Rev the engine in neutral and full throttle will only get a loping idle between 700 and 1400 rpm.  Shut down engine, restart, same thing... shutdown and start again and all seems normal.


Drive ~10 miles, get car smog tested (it passed)... make three  more stops in the course of another ~10 miles and all is normal.  Then at a traffic light idle starts to hunt between ~600 & 1200 rpm... then back to normal.  


After 4th stop and a ~1 hour cool down, I get the no power thing again (engine lopes and won't rev beyond 1,400 rpm at full throttle in neutral).  Car is difficult to restart, eventually starts but runs rough... I decide to try to limp the car the ~4 miles home (oil pressure and engine temp. normal through all of the above).  


On the way home, tons of surging , lack of low end torque, stumbling... then at a red light a repetitive lope: couple seconds at 1,400 followed by a short surge to ~1,700, then a dip to <1,000, then back to about 1,400... steady and repetitive, total cycle time of abut 4 seconds... it does this for the entire traffic light cycle.  Got the car home, coolant temp. still running steady at ~185F... but I could feel heat coming off the side of the car (rear)... hadn't felt that before... engine compartment seemed unusually hot.Car had about 1/8th of a tank of fuel when all this started, filled it up during the trip... had issues both before and after fueling.  No check engine light or other dashboard indication that anything is abnormal.  Two other incidents were similar to the above, though shorter as they happened near home.  One happened when the car was cold, the other happened after a ~50 mile trip where everything seemed normal.  Thought and ideas appreciated!      Jim








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