Parked overnight, rough cold start in morning

[APC7654]

So now this problem is consistent every morning; 2012 128i parked in garage, car cranks then stalls. It is repeated about three times and then it becomes a rough idle, but within 15 seconds engine runs smooth. From then on throughout the day, starts without a problem, but when sitting overnight, it becomes a rough start the next day.

This feels like a "choke" problem, although I don't think this has a choke, but probably an injector that pumps additional fuel at a cold start.

It also could be that the fuel line is not holding the pressure in the line, whether the fuel pump has a check valve to maintain pressure when engine is shut down.

Has anyone experienced this problem or have any suggestions.

[Gangplank]

Pull the codes?

[02Pilot]

AFAIK, there hasn't been a separate cold start injection used in BMW engines since the M20/M30 Motronic systems. Fuel pressure is a possibility. Physically checking at the rail before starting cold would be my preferred first option. Checking for fault codes is certainly advisable as well, of course.

[mackeroni]

Pretty basic advice... hope you are using nothing but top tier gasoline. Anything less could be lacking the detergency needed to keep your fuel delivery system clean.

Peace... Mack

[APC7654]

Been using Shell 92 octane. I don't have a code reader, so it looks like I'm going to take it into the shop for the codes.

[Matticus91]

Originally Posted by APC7654

Been using Shell 92 octane. I don't have a code reader, so it looks like I'm going to take it into the shop for the codes.

Highly recommend either getting a carly unit. You can read all the codes that way and much more than that. Other option is an el-cheapo code reader. They can be had for around $50-60 online.

Until then, any autozone/advance auto/pep boys will do a code scan for free. Take the codes down when then scan them, and go home and post them here and do some research on your own.

[02Pilot]

OBD2 scans are rarely helpful, and sometimes downright misleading. If you're going to buy a scanner, buy one that reads BMW-specific codes.

Fuel quality might be a factor, but it's likely secondary at most. If you've got an injector that's leaking when closed due to deposits you could put that down to fuel, but more often than not it's exacerbated by lack of flow due to light throttle application (admittedly this is not as common as it used to be). My solution to that is to dump a double strength dose of Techron into a quarter tank of fuel and drive ~50 miles hitting the redline with every shift. There will be no deposits remaining. Change the oil when you're done.

[chris_flies]

Could be your battery...if it is old, it's probably more sensitive to temperatures than it was last time it was winter. The stalling issue is elusive to me, could be spark plugs, but fuel something or other seems most likely. Good luck!

[Havocsteve]

I have a similar issue as well. 135i though. Cold starts when the revs get to about 800 after the initial start, it "chokes" and revs up to 1500 rpm. Only once it's warm it idles fine and such. No lack of power except if you try to drive off right away it, it almost stalls before the computer kicks in and revs it high to prevent stalling. I'm puzzled about this, as a leaky injector would cause performance issues all times and not just on cold starts alone.

[chris_flies]

Originally Posted by Havocsteve

I have a similar issue as well. 135i though. Cold starts when the revs get to about 800 after the initial start, it "chokes" and revs up to 1500 rpm. Only once it's warm it idles fine and such. No lack of power except if you try to drive off right away it, it almost stalls before the computer kicks in and revs it high to prevent stalling. I'm puzzled about this, as a leaky injector would cause performance issues all times and not just on cold starts alone.

My car used to do this, but after a few tanks of gas that wasn't from 7-Eleven or Sheetz, it stopped. It'd start, and then would run rough, then it'd blip into a really high idle, then settle down over about 10 seconds to a normal high idle, and then settle again over about 30 seconds to a standard idle. Never threw any codes, so I guess it was just a "phase"

[Havocsteve]

Originally Posted by chris_flies

My car used to do this, but after a few tanks of gas that wasn't from 7-Eleven or Sheetz, it stopped. It'd start, and then would run rough, then it'd blip into a really high idle, then settle down over about 10 seconds to a normal high idle, and then settle again over about 30 seconds to a standard idle. Never threw any codes, so I guess it was just a "phase"

I use just premium gas though. Shell and Petro only. I even put in a can of liquid moly fuel injector cleaner and drove the living piss out of it (probably need new winters now come next season). It only gets better with the warmer temperatures. Today it "blipped" but its 9 degrees celcius outside. When it was around -5 degrees outside, the damn car would shake when it "blips" until a few minutes once it settles. I have noticed idle surges, you can't see the rpm bouncing but you can hear it for sure. Waiting until the car blows up to find out what the issue may be. I know the mechanic had trouble getting the VVT to talk with the DME, wondering if my DME is going for a shit.

[chris_flies]

Originally Posted by Havocsteve

I use just premium gas though. Shell and Petro only. I even put in a can of liquid moly fuel injector cleaner and drove the living piss out of it (probably need new winters now come next season). It only gets better with the warmer temperatures. Today it "blipped" but its 9 degrees celcius outside. When it was around -5 degrees outside, the damn car would shake when it "blips" until a few minutes once it settles. I have noticed idle surges, you can't see the rpm bouncing but you can hear it for sure. Waiting until the car blows up to find out what the issue may be. I know the mechanic had trouble getting the VVT to talk with the DME, wondering if my DME is going for a shit.

Ouch, well, I have no idea. Run through an easy troubleshooting round; engine air filter, charcoal filter, oil filter, oil grade/viscosity, clean MAF/MAP sensor, etc. Hope you find a solution...

[Havocsteve]

Originally Posted by chris_flies

Ouch, well, I have no idea. Run through an easy troubleshooting round; engine air filter, charcoal filter, oil filter, oil grade/viscosity, clean MAF/MAP sensor, etc. Hope you find a solution...

Well soon it'll go in for an oil change at BMW, maybe they can have a look. It has to be fuel related according to my father. Since it chokes out when coming down to a idle. I might try cleaning the vanos solenoid with some card cleaner and see if that does the trick. I saw in some videos that it can get junked up and cause issues sometimes. But in all honesty, it could basically be anything.

[APC7654]

Originally Posted by 02Pilot

OBD2 scans are rarely helpful, and sometimes downright misleading. If you're going to buy a scanner, buy one that reads BMW-specific codes.

Fuel quality might be a factor, but it's likely secondary at most. If you've got an injector that's leaking when closed due to deposits you could put that down to fuel, but more often than not it's exacerbated by lack of flow due to light throttle application (admittedly this is not as common as it used to be). My solution to that is to dump a double strength dose of Techron into a quarter tank of fuel and drive ~50 miles hitting the redline with every shift. There will be no deposits remaining. Change the oil when you're done.

I dumped a regular dose of Techron, in the tank, and it appears to have helped. Now it only stalls once or twice before it finally starts. I'm next going with your suggestion, using the Techron concentrate in the quarter tank. Why is it that the oil needs to be changed?

[02Pilot]

It's just a precautionary measure, really. If indeed the rings are partially stuck (this is one of the things the Techron overdose can help with, though probably more common on older cars) you can get some oil dilution from the leakdown on the cylinder walls until the rings unstick and reseal. I doubt very much it's necessary, but I do it just to put my mind at ease.

Two bottles and drive the hell out of it. Get lots of fuel flowing through those injectors and lots of heat in the cylinders.

[chris_flies]

I ran some Techron through mine, put it in, filled the tank with 93, and the car idles smoother and starts slightly easier now. You might also take a look at/replace your fuel filter, depending on your car’s mileage. American gas, I’ve heard, is crap. Works fine for me, though...

[APC7654]

The car has 37,000 miles, so I wouldn't think it needs the fuel filter replaced, but you never know. If the strong dose of Techron doesn't do the trick, then I'm just going to bite the bullet and take it in mechanic.

[Havocsteve]

I'm only @ 94,000km. I wouldn't think to replace the fuel filter since it's still a new vehicle. My car still has the rough idle and bad cold start. I'm at a lost with this thing and it's making me want to move to a CX-5 or something since the snow will begin to fall.

[APC7654]

UPDATE: Still on my original Techron added tank full, down to 1/3 of a tank, and she's back to normal. Smooth start, smooth idle on the first crank. I'm still going to add the second bottle of Techron concentrate.

My theory is that some of the injectors leak overnight (due to carbon buildup), loosing fuel pressure in the supply line, which the fuel pump, at start, cannot keep up with. Does this make sense?

[02Pilot]

Originally Posted by APC7654

My theory is that some of the injectors leak overnight (due to carbon buildup), loosing fuel pressure in the supply line, which the fuel pump, at start, cannot keep up with. Does this make sense?

Yes (see post #7, above).

[APC7654]

02Pilot, you called it right. Thanks!

[Havocsteve]

I dumped a bottle of tectron and gave her hell (on the highway going to 200kmph) and even added a tank of 93 octane not long after. Still have cold start issues and such. Thinking come spring time, I'll replace my index 12 fuel injectors with the new index 13 ones.