Rough Idle and Check Engine Light flashing on and off
07-13-2018, 09:37 PM
#1
Instructor
Thread Starter
Rough Idle and Check Engine Light flashing on and off
OK I've got a slight issue with the C4 6 speed manual with 130K miles on it. Took it for a drive this afternoon for a few miles to run some errands. After returning, started the car back up and at the red light noticed the idle was a bit off/rough. Thought maybe it was my motor mounts causing a vibration (need to replace these) but going through the rpm's would be rough/stuttering until about 3k rpm where it would then it smooth out almost like a turbo kicking in. Then I noticed the check engine light come on and off for a few seconds and then the light goes out and then the same thing happens with the CEL for a few more times before I made it home. I do recall there being some uneven idle a few times prior to this incident but only for a few seconds each time.
I noticed that below 3k rpms the power was down, some hesitation and roughness. Fuel pump has never been replaced to my knowledge, nor the fuel pressure regulator or CPS or TPS. Could a faulty fuel pump be detected by a code reader? And would I faulty pump cause the CEL to come on? My initial inclination is that the fuel pump is going bad but I may be wrong. Spark plugs were changed about 5K ago along with fuel filter. Was running fine before today.
Any thoughts/ideas?
I noticed that below 3k rpms the power was down, some hesitation and roughness. Fuel pump has never been replaced to my knowledge, nor the fuel pressure regulator or CPS or TPS. Could a faulty fuel pump be detected by a code reader? And would I faulty pump cause the CEL to come on? My initial inclination is that the fuel pump is going bad but I may be wrong. Spark plugs were changed about 5K ago along with fuel filter. Was running fine before today.
Any thoughts/ideas?
07-13-2018, 09:52 PM
#2
Burning Brakes
Most likely a spark plug or ignition coil have failed. The check engine light will flash when there is raw/unburnt fuel being dumped into the catalytic converter. This can caused extreme damaged to the converter if driven for any long length of time. Need to have the computer scanned to see what cylinder it is and then do some simple test to confirm which coil or plug it is.
07-13-2018, 10:12 PM
#4
Rennlist Member
Cracked coil would be my first guess. If they have not been replaced, check them for cracks. The hot weather and or rain will trigger inconsistencies in spark.
07-13-2018, 10:15 PM
#5
Burning Brakes
Most scanners will be fine. Some times really cheap ones can be an issue. Cracked coils can be an issue on the 996. Porsche had a bulletin about replacing all of the coils if they are a certain part number. If one is crack it is highly recomended to replace all of them at the same time.