A little background - I’ve had my 2010 Grand Sport 6 speed, NPP, 39k mikes for 3 years. Only mods are MGW shifter and Mild to Wild switch. No issues whatsoever to this point. It goes in the shop once a year for inspection and maybe some routine maintenance.

About 2 weeks ago, it went in the shop for inspection and a front-end alignment. Got to love those PA potholes. The shop is a Chevy dealer where the mechanic is associated with the local Corvette club. For the inspection, I unplugged my Mild to Wild switch. Picked up the car, plugged in my MtoW switch, no issues at all. Drove it home and the car sat for several days before I went to drive it again. When I started it, the idle stumbled for a little bit so I feathered the gas and it eventual evened out. Drove the car the whole day. Restarted several times. No issues at all. Parked the car at the end of the day.

Car sat for a couple more days. Went to start it again and it just stumbled and stalled. Tried several more times with the same result. Thought I smelled some gas so I put the pedal to the floor and tried again. Car started, screamed to some high RPM and then back to an idle. Drove fine the rest of the day.

Thought I might have a bad tank of gas and was pretty low so I filled it up. Started up next day fine. Let it sit a couple of days and same issue with stalling. At first it seemed like it only would do it after it would sit several days, so I thought it might a leaky injector, but now it intermittent throughout the day. Sometime it starts fine, sometimes just starts an stalls. Foot to the floor and it starts right up and drives fine although I do think it runs slightly better when it starts normally. As weird as it sounds, I thought maybe it had something to do with the Mild to Wild switch since that’s the only thing that was changed before it started so I unplugged it. Same issue. And no codes/check engine light at all.

Called the dealer back, but they can’t get it in for 3 weeks. I did use the search function and found several posts saying that stumbling on the LS3 at startup was normal, but I’ve had the car 3 years and it’s never been like this. Any thoughts or pointing me in a direction would be greatly appreciated. Sorry for the long post.

 

Could be coolant temp sensor or maybe a dirty throttle body...do you have a scan tool ??...check your coolant temp and compare it to the outside temp after the car sits all night...if you can get into the generic OBD2 side of your scan tool also see what that reads...in generic the ECM can't substitute a temp value and you will read the actual temp the ECM is seeing...the temps (coolant vs. outside) should be within a degree or two of one another...NO stumbling on start up is normal !!

 

I had a similar problem on another car and it was a coil going bad... nothing special about a Corvette engine, it's just an LS series and GM built a million of them. Any competent shop with good diagnostic equipment should be able to track the problem quickly. YMMV

 

Thanks for the advice!

Hooked up a Tech 2 and had 6 codes. Bank 1 too rich/too lean; Bank 2 too rich/too lean; MAF voltage too low/too high. Thinking a MAF issue. Cleared the codes and cleaned the MAF sensor. Still the same. Check the codes again. No codes this time. Thinking about replacing the MAF sensor. Also looking at the crankshaft position sensor.

Checked the coolant temp. Looked to be close to outside so I'm leaning away form that. Agree about no stumbling.

I've had a couple of VW's that were notorious for bad coils. Had several go bad. This just feels different.

 

What were the exact DTC’s ??...if it’s a MAF DTC with a voltage circuit too low or too high I’d be concentrating on the electrical part of the circuit...it’s not a “performance” DTC like a P0101. To check the crank sensor you’d really need a graphing multimeter or a scope to test...a DVOM’s refresh rate is to slow to pick up a bad signal...what do your fuel trims look like ??

 

Unfortunately, I cleared the codes last night while I was working on it.

The good news is I took a chance and replaced the MAF and it appears to have solved the problem. Only had a chance to take it around the block and start it a couple times, but it started right up every time and the idle settled right down to where it should be, I'll get tit on a long run tomorrow. Thanks everybody for the help.

 

C5 Diag - looks like you were right. Replacing the MAF sensor worked for a couple of days and the problem returned. Checked the codes and it's showing P0102 Mass Air Flow Sensor/ Low Frequency. From what I've read, the most likely issue is a bad ground, Borrowed an oscilloscope to put on it tonight.

I've read there are 12 or 13 grounds on the car. Anyone know where the MAF sensor ground is?

 

I believe your MAF ground is G106 which is a body ground on the right rear side of engine below the ECT sensor. Maybe another member can verify...If you disconnect the MAF connector you should have 12 volts on the PINK wire, 5 volt reference on the YELLOW and the ground which you need to check...and resistance checking of ground circuits using an ohm meter is incorrect !!...what you can do is use a DVOM and measure voltage from the yellow 5 volt signal to the black ground wire...you should see more than 4.5 volts !!

 

Checked everything and appeared to be having intermittent ground issues. Replaced the pin/pigtail at the connector, soldered it into the harness and cleaned the G106 body ground on the right rear side of the engine. Same results. Bought a replacement connector from GM, pulled the pin/pigtail from the new connector, put it into the old connector and ran it to a local frame ground. Problem solved! I'm assuming I have a broken/frayed wire somewhere in the harness. It's running great now, but I'm going to have to figure out a more permanent solution.

Thanks for all the help!

 

Great news !!...If you can get a headlight bulb with connector (55 watts) at your local parts store and make yourself a load tester with it...hook the power lead to battery positive and the ground lead to whichever ground you are checking...see if that headlight bulb glows bright on that suspect ground...load testing is the BEST way to check grounds and NOT with an ohm meter !!...you have to make sure that that current can get back to ground...MANY don’t have a clear understanding of this concept !!

 

Ok. Had to post an update to the story.

As I mentioned, I put the frame ground on Thursday after work. Started the car and it ran great. Drove it around the remained of Thursday night – no issues at all. Got up Friday morning. Started fine. Drove it to work and around at lunch - again no issues. Got up Sunday morning. Went to back it out of the garage, wouldn’t start again. Same issue. Since I already had an appointment scheduled at the dealer for Monday, I decided to splice the pigtail back into the wire harness and drop it off at the dealer Sunday night for them to look at Monday morning. The tech at the dealer does a lot of work with the local Corvette club and everyone swears by him.

Got a call from the dealer Monday around noon. They went to start the car and the battery was dead. Really odd since I’ve never had an issue with it, but they said that they tested it and it failed their test. They also said the cables were slightly loose. The plan was to install a new battery, tighten all the cables and try again in the morning.

Got a call today around noon again from the dealer and this is what they told me. They installed the battery, let it sit inside all night and it started right up in the morning – no issues. When the tech took it for a test drive, the car almost stalled on him and he had to limp back to the dealership. Thinking it’s now a fuel issue, he checks the fuel pump, pressure, etc. Everything passes and still no codes. He says he’s stumped (his words, not mine) so he’s going to start at the front of the car and work back on every system until he finds the problem.

When he pulled the air filter off, he noticed the carbon pouch had come unglued from the housing and is only attached along one edge. When he gives it gas, depending on how the air flows, the pouch swings down and blocks almost the entire intake of air and the car stumbles and stalls. Pulls the pouch off, re-installs the air filter and everything is running fine – for now!

I’ve never heard of anything like that before. Thought I’d post in case anyone else runs into a similar situation