Will do and update
6
Unsolved Issue, Slight Rough Idle - no CEL
- Thread starter Buhrady
- Start date
Haven't noticed it doing that, but also haven't been paying too close attention. I'll monitor this. Also PCV was replaced with latest revision at 86k miles.
BudgetPhoenix
Autocross Champion
If you're noticing you're not noticing your tach moving at all and it still feels rough id still pull all your mounts out and inspect them.
Went for a good drive and checked today. Tach needle is dead still at idle. Might be the mounts
Francoleon91
Drag Racing Champion
dude, honestly, it could be a million things. Best of luck. let us know if u ever figure it out.
Well, an update here - hooked up VCDS to monitor the live data yesterday, as suggested on an above comment.
The car was warm - we let it idle and watched the misfire count. For each 2-3 minute span of idling, it would pick up roughly 3-5 misfires total across all cylinders. They would pop up on all cylinders randomly, so this eliminates a bad injector or bad engine mounts. Still never enough to throw a CEL.
Only thing that stood out to my mechanic was he noticed that the car was running slightly rich at idle. Car was pulling fuel trim at roughly -5% to -6%. He said this is slightly abnormal.
We went for a drive around the block with VCDS hooked up. Car was still running slightly rich, until I would roll into the throttle it would level out to a normal level.
Interesting thing was that once he reset everything on VCDS, misfires went away temporarily. Let it idle for 5 minutes and nothing came up, and it felt smoother. I did a ~45min drive after that and they were back by the end of it. So the car is incorrectly adjusting for something.
Timing was still floating around -2.6 to -2.8 on our drive, so that's still no issue.
We were both at a bit of a loss. I'm not an expert by any means - any thoughts?
The car was warm - we let it idle and watched the misfire count. For each 2-3 minute span of idling, it would pick up roughly 3-5 misfires total across all cylinders. They would pop up on all cylinders randomly, so this eliminates a bad injector or bad engine mounts. Still never enough to throw a CEL.
Only thing that stood out to my mechanic was he noticed that the car was running slightly rich at idle. Car was pulling fuel trim at roughly -5% to -6%. He said this is slightly abnormal.
We went for a drive around the block with VCDS hooked up. Car was still running slightly rich, until I would roll into the throttle it would level out to a normal level.
Interesting thing was that once he reset everything on VCDS, misfires went away temporarily. Let it idle for 5 minutes and nothing came up, and it felt smoother. I did a ~45min drive after that and they were back by the end of it. So the car is incorrectly adjusting for something.
Timing was still floating around -2.6 to -2.8 on our drive, so that's still no issue.
We were both at a bit of a loss. I'm not an expert by any means - any thoughts?
Joe_Mama
Autocross Champion
I think youre on the right track here though. Running slightly rich definitely seems to be cause of your random, sporadic misfires. So lets focus on that.
You have already addressed things like fuel and ignition so it must be air. You are running rich fuel mixtures for a reason and that reason must be 1 of 2 things:
1) Air Leak
- introduction of unexpected fresh air ANYWHERE downstream of the MAF will throw off your calculated A/F ratio and cause random misfires. Check your intake, turbo coupler, intercooler pipes, diverter valve, PCV etc.
2) Faulty Sensor
- I think this is the more likely cause and there is a few you need to look at. First of all, using VCDS you can record the Lambda reading, or basically how much voltage is running through your O2 sensor. A fouled or faulted o2 sensor can cause your engine to run rich. It may be just at the value where it doesnt trigger a CEL but is still sending incorrect readings. I believe voltage levels above 1 indicate rich, but I could be wrong. Next, check your MAF. Get some cleaner and spray it down if you havent already. If your MAF readings are off you will run rich.
I will say, the reason i am leaning towards a faulty sensor is due to your last post where you describe how when cleared and reset, the car ran no misfires until after driving for roughly 45 minutes. This means when reset to default values, the engine runs great, right up until the ECU has had time to collect enough data and adapt the car to what it THINKS is the right A/F ratio.
Try unplugging the MAF and running the car. See if it runs no misfires again. If it runs BETTER with the MAF unplugged, you just found your problem.
You have already addressed things like fuel and ignition so it must be air. You are running rich fuel mixtures for a reason and that reason must be 1 of 2 things:
1) Air Leak
- introduction of unexpected fresh air ANYWHERE downstream of the MAF will throw off your calculated A/F ratio and cause random misfires. Check your intake, turbo coupler, intercooler pipes, diverter valve, PCV etc.
2) Faulty Sensor
- I think this is the more likely cause and there is a few you need to look at. First of all, using VCDS you can record the Lambda reading, or basically how much voltage is running through your O2 sensor. A fouled or faulted o2 sensor can cause your engine to run rich. It may be just at the value where it doesnt trigger a CEL but is still sending incorrect readings. I believe voltage levels above 1 indicate rich, but I could be wrong. Next, check your MAF. Get some cleaner and spray it down if you havent already. If your MAF readings are off you will run rich.
I will say, the reason i am leaning towards a faulty sensor is due to your last post where you describe how when cleared and reset, the car ran no misfires until after driving for roughly 45 minutes. This means when reset to default values, the engine runs great, right up until the ECU has had time to collect enough data and adapt the car to what it THINKS is the right A/F ratio.
Try unplugging the MAF and running the car. See if it runs no misfires again. If it runs BETTER with the MAF unplugged, you just found your problem.
Agree with your input - going to give this a try on the weekend. Will update, thanks!
I spent some time listening for that, but nothing.
Timothy Bryce
Ready to race!
@Buhrady I know this might seem like a long shot; I had a slight misfire at idle when I bought my car; was more obvious once hot. I also had some codes thrown. As the car was new 'to me', I replaced PCV, coils, spark plugs and air filter all OEM. Misfire was less obvious but still there. My mechanic suggested the evap / purge valve but strangely he also suggested that I should change the charcoal canister at the same time as in his experience these often go faulty (whatever that means).
Anyway, as the evap valve is a pig to change I started with the cheapest / easiest first and bought a cheap chinese canister and hose off amazon. To my amazement it cured the misfire and the codes disappeared! I then replaced the canister and hose for genuine.
If it wasn't that I'm in the UK I would send you the chinese canister for free just to try. You could however probably get one from a scrapyard for next to nothing; worth a try?
Anyway, as the evap valve is a pig to change I started with the cheapest / easiest first and bought a cheap chinese canister and hose off amazon. To my amazement it cured the misfire and the codes disappeared! I then replaced the canister and hose for genuine.
If it wasn't that I'm in the UK I would send you the chinese canister for free just to try. You could however probably get one from a scrapyard for next to nothing; worth a try?
If there are no boost leaks I’d take a look at the n80 valve...the original n80 had 2-3 check valves attached to the hard plastic line that snakes it’s way under the manifold. My n80 was fine but the check valves were not (air moved through the check valves...both ways!). Btw I replaced the entire fuel system (HPFP, lpfp, injectors) as well as EVERY sensor in this engine. Nothing cured the misfires until replacing the n80.
Certainly worth a shot - adding this to my list.
Well pulled apart the intake this weekend, pulled out the MAF and cleaned it with proper MAF sensor spray. Let it dry for a day and installed it this morning. I also adjusted the orientation of the MAF back to stock location (11 o'clock). It was perfectly north south previously. Doubt this makes a difference but not taking chances anymore lol. Went for a 30 min drive just to see - I don't have VCDS handy for live data however with my "butt data" the car definitely felt a bit smoother all around. This could be attributed to the MAF never being cleaned in 150,000kms and a bit of placebo effect. Still felt some slight vibrations though at idle after awhile. Going on an hour plus drive tomorrow. This should tell me if it truly fixed it or not, but it's definitely an improvement as is.
If no, going to stop in at my mechanic at some point to get the lambda reading of my O2 sensor as suggested, then work through (from cheapest to most expensive of):
1. MAF sensor
2. O2 sensor
3. N80 valve
4. Charcoal canister
I'm 99% certain it's one of the above based on the symptoms.
If no, going to stop in at my mechanic at some point to get the lambda reading of my O2 sensor as suggested, then work through (from cheapest to most expensive of):
1. MAF sensor
2. O2 sensor
3. N80 valve
4. Charcoal canister
I'm 99% certain it's one of the above based on the symptoms.