Hey y'all. This morning when I was leaving for work I noticed, at idle, a considerable misfire in the GXP. After a 50 mile drive to work the car was idling fine. I plan to take it to the shop this evening but first wanted to see if anyone here might have some ideas as to what it could be.

Since my car was new, it doesnt like to run well when cold. even when it'* warmer outside it can sputter when I get on it cold. I also have to get on it to "clear it out after I let it sit at an idle for periods of like a half hour whibh is unavoidable when I have my Aunt with me like when I shop and it'* cold outside. Also,... are you running regular fuel. The Northstar really wants better octane with higher than normal compression and this would be more apparent in cold weather.

Not that I am trying to diagnose your problem on-line, nor am I suggesting that this is your problem, but my 04 GXP really b!tched and moaned (slow starts on cold days)when I accidentally put a full tank of regular in it. I don't think it misfired but my fuel econ went down to 14 city and took two tanks of premo to get back in the 19/20 range, city.

I have used nothing but 93 Octance in the car since I bought it new. Actually, I have never used any less in any of my cars.

However, I found out this morning that the fuel station I always use had a problem with one of their storage tanks and will be closed for a few days. Could be something to do with it.

I filled it this morning at a different station and by the time I got to work it was back to its normal self.

Hopefully this works.

Thks.

Be very wary of fuel stations with old tanks. Who knows what got into your gas? Water? Rodents? Jimmy Hoffa? I completely avoid stations with old tanks (e.g. old gas stations).

I jsut went outside and let the car idle for about five minutes and it ran very normal without misfiring.

The fuel station I normally use is very old. I filled up this morning at a very new chevron station. Like you said, could have been anything in the gas...

My 18k mile 05 GXP does, for lack of a better word, occasionally “shake” a little for 5 - 10 seconds or so when I first start it up. Nothing major, but you can feel that the engine is not quite running smoothly. I don’t think I’ve noticed it happening on a cold start first thing in the am, but maybe if the car has been sitting for an hour or 2.

I run nothing but 93 octane. If anything, I believe higher octane fuel would contribute to the problem on a cold or cool start since it burns more slowly and is slightly harder to ignite than the low octane stuff.

Finally figured out the problem with the misfire. Turns out that the coil for #5 cylinder was starting to fail and subsequently caused a misfire at low rpm. It took the dealer nearly 5 days to figure this out. Got the car back last night and I am happy to say that the car is back to normal.

Well at least I got new plugs and new injectors for free.

It was missing with out any codes ?
odd isnt it