Odd idle only when cold, misfiring

So I've been having issues with my '08 LGT 5eat, it has 33k miles on it. Since the weather has been getting cold I've been experiencing a rough idle when the engine is cold, pretty much right after the blue light goes off and before fully warmed up.

 

My boost gauge is reading -15 inHg vac and boost is a hair lower than what I was tuned at. 15 opposed to 17. Once the car has warmed up it runs fine and idles normal. I got a CEL last night and there were misfires on all 4 cylinders and a system too lean code.

 

This morning I pulled everything apart and tightened everything I could- thinking it was a vac leak, no fix. I also cleaned the MAF. I searched the forum however could not brandish an exact issue. Any ideas? No other abnormalities are noticed when driving, idling. My oil level is a bit high, would that cause an issue. 1/4" over the full mark when cold. Thx

Actually boost is reading 17 now, however the first start after ecu reset it idled rough after blue light went off.

Last week I had CEL I dumped a can of Seafoam in the gas tank, idles much better now. $10.00

 

Get it the auto parts store. The guy's at the counter know what your looking for.

mines been doing the same thing as well,

 

every morning i drive the car, it idles ruff and i keep getting a P0171 (system too lean bank 1) P0301 (cyl 1 misfire detected), P0302 (cyl 2 misfire detected), P0303 (cyl 3 misfire detected)

 

Ironicly thiough mine started shortly after receiving my car back from getting the transmission replaced.

Weren't some people saying that Seafoam is actually a really bad idea for our vehicles? Or were they talking about a different additive.

There shouldn't be ill effects from using seafoam in the gas tank. Some people say using it through the vac line can clog up a cat if you have enough carbon that is burning off.

 

 

 

Seeing as this issue ONLY happens when the car has been sitting in 30 degree weather overnight, would an intake manifold gasket be the culprit? It seems that once the engine has warmed, something, some gasket might expand and seal. It's very odd, the engine does not consume any oil, does not smoke or blow smoke. The battery might be on it's way out but I don't think that's related to a misfire. I put a can of seafoam in the tank, if the problem subsides a little, then I'll know it's injection/fuel related....

my car is going into service tomorrow about the issue so we will see. Im going to suggest the IM gasket to see what they have to say.

Lemme know asap!! Please.

No boost leak, did a test tonight.

I get this same issue. Car has about 70k on it tho. Dealer said nothings wrong. :/

 

MAF is clean, can't find any leaks, tried different gas stations, oil change. 60k service changed plugs, and everything else involved in that service. Dunno what else there is to do.

 

Totally stock.

 

Subscribed.

I read somewhere that a bad battery can cause misfiring? My battery has been cranking rather slow, I wonder if there's a connection....

 

Reduced voltage for coil pack to fire, especially in a cold environment if your battery is on the weak side.

Just scanned my car and I got misfire in 3 and too lean. I cleared the code and the car is idleing rough. Gave it a little gas and the RPM goes down to 500 and I can feel the car dying, then it raises it to 800-1000. Its been happening alot recently and that is why I bought me a obdii scanner.

 

 

Do you think its from the tune bmx045? Im in the market for a new battery...isn't yours an 08? Kinda soon to be replaced.

Yeah, but it cranks over weak especially in the cold. This seems to happen ONLY after the car sits overnight and in the cold, meaning the battery *might* lose a charge in that time period, also the cold weather being even harder on the battery. It's something to think about....this battery is about 3 years old now, car was manuf 11/07. In all honesty I think in new england we need a stronger cold crank amp battery, or better battery in general...

Guess I'm going to autozone to pick up the battery tomorrow. I might get the 26R with 575cca or the 47 with 590cca. Hopefully this will help.

These cars don't take too much power to start, I remember getting the duralast gold at AZ with 1000cca for my jeep, that battery was AWESOME. It was only like $76.

I had the same problem with my 07. I did everything you guys are talking about and it did no good. My problem started after the dealer did the turbo oil line recall service. I had it into the dealer several times and even tried a couple of different dealers with no sucess. While upgrading to stage 2, I got a pro-tune and they found that my turbo inlet pipe had a tear in it and was sucking air after the MAF causing the car to run lean when it got cold enough. I replaced the turbo inlet pipe with a new silicone AVO system and havn't had the problem since. I suspect you have an intake leak "somewhere". Mine happened to be at the turbo inlet pipe.

Good luck!

but I did a leak test and there's no leak!

Yesterday I was driving...I put it in S# and floored it. My car wouldnt go and I can feel the car hesitating and it just wouldnt go. I tend to smell gas in the car. you guys thing spark plugs?

but I did a leak test and there's no leak!

 

Hmm... Did you pressure check from the MAF forward? How much pressure? Mine didn't start leaking until I put about 10 PSI on it since there was oil that was holding the hole shut. After I hit that it leaked like screen door on submarine. Apparently under vacuum it would open right up.

My only other guess would be intake gasket leaks. I was always suspicious of the plastic manifold and aluminum heads.

Cold temps are always tricky, and it may be a software issue with the ECU.

 

But it can also be a sensor that doesn't read right until it's warm.

 

Dirty injectors may also make cold starts more cumbersome.

 

And oil viscosity plays a role too. If the oil is thicker than what the mapping expects it can make the engine quirky. But I suspect that emissions demands plays a role in this behavior.

I am having the same issue. This morning, the temp gauge on the dash read 9*F. My battery has been cranking over kinda slow, especially this morning. Today was my first experience with the rough idle.

 

When I say rough, I mean it. The car felt like a muscle car the way it was shifting back and forth for a few seconds. After it warmed up, it was smooth and normal.

 

My first thought was to change oil weights, but I am most likely going to purchase a new interstate from work and see if that cures it.

Wouldn't really hurt to try a 5w anyway....

That's what mine feels like blackGT. Its a rough muscle car feel. My car nearly didn't turn over after 3 cranks....it was close. But no battery light indicator. I changed the oil recently and using syntec 5w-30....shouldn't be the culprit though.

I just tightened all my FMIC and CAI clamps and checked all the hoses. Everything felt fine. Started my car....CEL....came on. Running lean...WTF. Clear that code and after that...it felt fine. Can't wait what tomorrow has to bring. Also, my exhaust pipes are super black. Cleaned it this morning, got breakfast with the wife and came home...black.

 

I just changed my oil to Gastrol Syn 5w-30 and always used syn so I also dont think thats the problem. I'll give it another week then give Bren a call, maybe the tune needs a little touch up.

I mentioned it to Bren since mine is Bren tuned as well, he thinks it's mechanical and not tune. However it would be a good idea to log and double check.....lemme know

Check the intake manifold gaskets. My car had the same symptoms. Dealer couldn't reproduce until I told them to spray carb cleaner around the manifold when the engine was *stone cold* and left idling to slowly warm up. If it was started, shut off (leave for a few minutes), then started again, the heat generated would be enough that the problem wouldn't occur. When they followed my instructions, they said the idle smoothed right out. They swapped the gaskets and the car has been smooth so far this winter. The dealer said that the gaskets were flattened in some spots. I guess they got pinched when installed at the factory.