samotlietuvis

Guys,

My 08 C6 M6 50k miles vette developed stumbling problem in low RPM’s at light throttle that has been getting worse for the last few months. I have lean left bank code P0174 as well. The car idles smooth, but when accelerating at light throttle from 1200 to 1800 RPM’s, it bogs big time. The stumbling is much worse when the car is cold. The stumbling in very noticeable when going downhill with cruise control on. Also, my idles very erratic when rolling in neutral gear (600+/-400 RPM’s). Once I was rolling down in neutral for ~3 miles and my car shut down due to RPM oscillation. Other than low RPM low throttle stumbling, the car runs fine and gets good gas mileage.

I suspect that my MAF is not giving smooth reading at the low RPM light throttle condition. What doe not make sense is that I am getting a lean code for left bank only, but not for both banks. Could it be that spark plugs or O2 sensor went bad for 1 bank? I have replaced my air filter ~6 months ago. A month ago I checked for any air leaks by taking my intake apart again and putting it back together. I did not find any smoking gun and my problem is still there.

A few questions:

1) When I replaced the air filter, I could not remove MAF connector, so I just removed MAF sensor. Later I reinstalled the MAF sensor. To my surprise MAF sensor does not have any rubber gasket: just plastic to plastic contact and it does appear that it should have a gasket. Is vacuum leak at MAF mounting location possible?


2) GM has a TSB directing the tech to check and make sure the shroud is sealed (Subject: Corvette Lean DTCs P0171 P0174). Recommendation/Instructions:
DTCs P0171/P0174 may be caused by a gap between a body close out panel combined with some frame plate holes. Could that be the answer to my problems? Will GM perform TSB since my car is out of bumper to bumper warranty, but still under general 100k mile warranty?

3) Since I just checked for air leaks in my intake a month ago (none were found), should I look somewhere else like plugs and O2 sensors.

Thanks, Tomas

samotlietuvis

To answer one of my own questions:

GM will not perform non-safety related TSB if the car is out of bumper to bumper warranty. If it is a letter you received from GM regarding safety recall (like steering wheel ABS fix), then the fix will be free. But if it is a TSB regarding shroud sealing on front bumper, then the fix is not free. Just wasted $105 for nothing. Hopefully this info will help.

I plan doing the shroud fix myself, will report the results back

0Brian@RPT

If you are running lean, that can cause all kind of issues. In your case, you may not be running lean but, the ECM is dumping in extra fuel causing a overly rich condition. The P0171/P0174 are from unmetered air getting into the system downstream of the MAF. Any mods or is it bone stock? Do you have a catchcan? I would get the Vette scanned by a fellow board member and that can reveal some data that will lead you in the correct direction.

taken19

Check for the obvious first - pull the plugs to look for indications of fouling, etc. Check plug wires for looseness. If you suspect an O2 sensor, swap a pair and see if the problem swaps to the other bank. You could do that with wires, coil packs and even injectors if you wanted to. Swap one thing at a time to get a clear picture of what could be causing the problem. If it were an air leak, I would think that the idle would be rough, not necessarily light acceleration. Do you have the ability to clean the LS3 MAF element? If so, use a Q-tip and rubbing alcohol to remove any oil or dirt, but be extremely careful.

Those are all things you could that doesn't cost you any money, just a bit of time and patience.

samotlietuvis

My vette is 100% stock, no catchcan. I triple checked any MAF leak with no luck. I already cleaned MAF element and I was careful and used Q-tip with electrical cleaner. Did not check plugs or wires yet, but I do plan to replace the plugs this weekend (50k miles already). The car idles nicely at 600 RPMs when it is not moving, and it runs well when it is not under light throttle. The lean bank codes keeps coming in and out (like it turns on, stays on for a few days, and then comes off for a few days) .

samotlietuvis

Fixed my stumbling problem . When I removed air filter, I noticed ~2” gap between upper radiator air baffle and beam (GM TSB calls out no gap, and to fix the beam holes), with the gap being wider on one side. The retaining clips that hold upper radiator air baffle and beam together were missing all together. When I looked underneath the car, I noticed that my skid pad (aka radiator support) is broke on one side (6 months ago hit a piece of truck tire at night…). I ordered a new skid pad from eBay for $250 shipped.

The TSB fix took me ~1 hour to do. First thing I did was went to Pep-Boys and got lucky (funny how infrequent that happens) – I found push in plastic clips (tree like short length, "Body-Tite" brand 3/8” hole diameter part # 45812, $2.5 a set) that was exactly what I needed to bring the beam and upper radiator air baffle together. To push in the pins one will need to raise the front of the car and push the pins from the bottom. After installing the pins, I got under the car and sealed the remaining 1/10” gap with HVAC aluminum tape. I also used the aluminum HVAC tape to seal all of the beam holes. If your pins are not missing, then all you would need is just some good tape (I recommend HVAC aluminum) to perform a TSB fix that can be done in ~15 minutes.

The car runs very smooth – no more stumbling or hesitation at any RPM’s any load.

taken19

Good to hear. I wouldn't have guessed that. Did that lead to some sort of vacuum leak? I can't connect the dots to see how that would cause your problems.

Either way, good job. Post pics if you can so others may be able to learn more from this.

samotlietuvis

I wish I took pictures when the car was raised. I will take pictures when I replace the skid pad (if I do not forget).

Although I did not design, nor did I calibrate MAF, from my best understanding, the gap was causing not-smooth air flow to air filter, which in turn was causing noisy MAF readings, and in some cases was throwing MAF readings off because that MAF samples only small area of air intake (if MAF sampled area would get a gush of air but the rest of area would not, the transformed calibrated reading would “assume” that the entire area got the gush and would read higher air intake). That’s just my $.02.

jmagilto

Thanks for your post. I have the identical issue on my 2010 GS. I even replaced the MAF.

I will put the car up and try to see if I can see what you describe
jer