I have a 2009 G37X that I park during the summer months. I typically try to start it and drive it every couple of weeks but over the last 2 months or so it stayed parked. It is in my garage hooked up to a trickle charger. Today I decided to take it out and it started up fine and sounded as it always has. I let it idle a minute and pulled it out of the garage and let it idle a couple more minutes. Everything sounded and felt normal.

When I started driving it, and then came to a stop sign the idle was sitting at about 600RPM (not too much out of the ordinary if I recall normal idle RPMs) but sounded like the engine is about to cut out but never did. Upon accelerating normally it was very lethargic. Operating temperature was up to normal and if I pushed the throttle any more than about halfway or up to wide open the RPMs were violently bouncing between 3000 and about 3300 with the car bucking and the car would not accelerate at all. If I went back to partial throttle it would accelerate VERY slowly but very obvious that it is missing a lot of power. The sound also was very different than what it should sound like during cruising speeds.

After about 10-12 min of this the "service engine soon" light started flashing. I parked the car and turned it off and then back on. All the symptoms and the flashing light were still there.

Has anyone experienced these symptoms? I would like to DIY this but it has been a long time since I tinkered with my vehicles... haven't had the time. But I have in the past gone as far as a top end rebuild. So I can follow instructions. The problem is with limited time I don't know where to start - inspect hoses, check for vacuum leak, clean throttle body or go right for plug in injector or coils? Any help and input would be appreciated.

 

I would suggest starting with the injectors and going backwards on the fuel system. Possible the gas has sat over to long.

 

Go with goose, check your fuel. Gas has a shelf life of 30 days or so, but I have had luck with it sitting longer in my lawn mower.

If possible, get some fuel out of there and try to light it on fire. (BE SAFE!!! I take zero responsibility for and harm or lost eye lashes) if it lights up, try cleaning it out. If it doesn’t spark very well, throw a few gallons in the tank and run it, see what it does

 

Siphon out as much as you can, pour some HEET in there, and fill 'er up.

The best way to remove bad gas from the tank is a process of immediate displacement, siphoning out the old gas while immediately placing high octane gas in the tank as quickly as possible. Depending on the amount of water in the tank, you may want to drain the gas tank and leave it empty for a while so that it can dry out.

 

I park my M5 over the winter months for 4-5 months without even starting it and it starts up and drives just fine every spring. Same with the G in past years. I would not touch it all summer. This time it was only a couple of months. What is different this time? Could it be anything else?

 

Did you check the code? That's the best place to start. Could be a number of things.

 

Actually that is a good point... I have not. The only OBDII cable that I have connects to a laptop via RJ45 (used it to code some options on my M5) but I do not have a OBDII code reader. I meant to look in to it because I think there are apps today on mobile devices that can do the same thing with the purchase of a OBD cable that connects to the mobile device but I haven't looked in to that yet. Let me see if I can get something online or local in the next day or two.

 

Your local auto store will also likely check it for free if you're comfortable driving to them

 

There' s a product called stabil. Used that with the motorcycle/snow blower when parked for the season (4-5 months storage). Both usually fire on the first or 2nd start and run without hiccups. Otherwise, they say gas starts to deteriorate after ~30 days. Suffice to say, had a relative with an impala ss (mid 90's) that was parked for a good 3 or 4 years. Car needed a new battery but did start and run (quite well too). It had a rodent infestation problem, but that was another matter

 

my 0.002 is that its gas t hat went/is starting to go bad, did you get it from a different station than last time? maybe the station you used got some less "fresh" gas this time

 

2 months is nothing.

Something else is amiss.

Check the codes.

 

Okay I have an update...

I decided to start the car back up this afternoon after the overnight "reset" ... and voila it started and idled normally again and no warning indicators on the dash. I drove it and no issues but I stayed easy on the throttle. I went straight to the gas station and filled up a full tank of my usual premium. Drove it a while including in sport mode and wide open throttle. Seems like all is back to normal.

That was very odd but the original suspicions here were correct... seems like it was bad gas. Thank you all for your help! Now on to diagnosing a few other minor issues that I had been neglecting since late Winter - gas level sensor seems to be on the fritz... when the car is low on gas that needle is all over the place from bone dry to half-tank! Also after it sitting for a bit it seems to have some "rubbing" issues in the rotors... also need to diagnose a small (oil) leak from under the engine that is very sporadic and temperamental - its there one day and gone the next.

Thanks to you all again for the help!