Random Misfire Issues
08-21-2015, 02:08 PM
#46
Thread bump. This one is a GD little gremlin. Car would start fine and idle for about two minutes, but when it would go to low idle, misfires on cylinders 4, 5, 6. I knew plugs and coils would not fix the issue after reading multiple threads on this topic. I replaced them anyway and no luck. In my case, it ended up being the variocam solenoid on bank two. When the car would go to low idle on a cold start, it would create too lean of a mixture on bank two and misfire. Now she's purring like a kitten and I'm back to daily driving. Hope this might help others with similar issues.
Another similar thread with more great insight from Macster
https://rennlist.com/forums/997-foru...ine-light.html
Another similar thread with more great insight from Macster
https://rennlist.com/forums/997-foru...ine-light.html
10-08-2021, 05:34 PM
#47
Rennlist Member
i just went with misfires myself. here is full list of issues, probability from high to low:
1) dirty/bad MAF sensor - VERY probable for misfires on all cylinders at once. test is simple - disconnect power, disconnect cord from MAF sensor, start up car and drive around not going higher than 4K RPM. if misfires stopped and car sounds OK - it was MAF.
buy MAF cleaner first prior to buying new sensor and pour whole can into MAF sensor, from all angles, inside, out, etc, but do not touch any parts. with some luck it may help, or may not. if you have durametric - at ignition switched on MAF data reading should show below 1.1v or so as I understood.
2) bad coil/coils. that was my case - bad coil on 2nd cylinder. if you do not have spare coils and have consistent misfire on one bank and not other - swap coils and see if misfire moves to another bank.
3) valves - stuck valve lifters. bad luck issue, big $.
4) bad DME - people say sometimes it happens, DME just go bad, also quite big $ to replace.
search around on 996 forum for this stuff, it has more info, also search on renntech site.
1) dirty/bad MAF sensor - VERY probable for misfires on all cylinders at once. test is simple - disconnect power, disconnect cord from MAF sensor, start up car and drive around not going higher than 4K RPM. if misfires stopped and car sounds OK - it was MAF.
buy MAF cleaner first prior to buying new sensor and pour whole can into MAF sensor, from all angles, inside, out, etc, but do not touch any parts. with some luck it may help, or may not. if you have durametric - at ignition switched on MAF data reading should show below 1.1v or so as I understood.
2) bad coil/coils. that was my case - bad coil on 2nd cylinder. if you do not have spare coils and have consistent misfire on one bank and not other - swap coils and see if misfire moves to another bank.
3) valves - stuck valve lifters. bad luck issue, big $.
4) bad DME - people say sometimes it happens, DME just go bad, also quite big $ to replace.
search around on 996 forum for this stuff, it has more info, also search on renntech site.
An immediate drop to idle or clutch in with higher revs removed it immediately - so, looks like coils. It was quite a while and still this is the thread that comes up.
So, apparently i had 10 years on coils i got replaced in 2011. Not too shabby.
Last edited by utkinpol; 10-08-2021 at 05:49 PM.
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