Another cold start hesitation question.. anyone got it resolved? - The Unofficial BMW M5 Messageboard (m5board.com)

Anzir · 13th May 2005, 17:16

I've had an SES for the banks 1-4 pre-cat O2 sensor and a cat. converter on that side as well, so I switched out the O2 sensor a month ago and as of late, I've noticed that the car has some SEVERE cold stumbling that goes away very quickly.. even before I drive 1/2 a mile. It's almost as if someone hits a button and the hesitation just disappears. After that, it's fine, and it only occurs in the morning on a true cold start. I've read that people have attributed it to the MAFs, an O2 sensor, and have even called it normal, but could this be something due to a faulty cat. converter? I just wanted to get some opinions before I get it taken in for a check. I've also read that a Powerchip upgrade will do the trick, and that's a nice excuse to do it.

gsfent · 14th May 2005, 01:37

Quote:

Originally Posted by Anzir

I've had an SES for the banks 1-4 pre-cat O2 sensor and a cat. converter on that side as well, so I switched out the O2 sensor a month ago and as of late, I've noticed that the car has some SEVERE cold stumbling that goes away very quickly.. even before I drive 1/2 a mile. It's almost as if someone hits a button and the hesitation just disappears. After that, it's fine, and it only occurs in the morning on a true cold start. I've read that people have attributed it to the MAFs, an O2 sensor, and have even called it normal, but could this be something due to a faulty cat. converter? I just wanted to get some opinions before I get it taken in for a check. I've also read that a Powerchip upgrade will do the trick, and that's a nice excuse to do it.

Have them check the auxiliary/ secondary air pump, which should kick on when the car is cold.
Regards,
Jerry

hudson · 14th May 2005, 07:48

Quote:

Originally Posted by Anzir

I've had an SES for the banks 1-4 pre-cat O2 sensor and a cat. converter on that side as well, so I switched out the O2 sensor a month ago and as of late, I've noticed that the car has some SEVERE cold stumbling that goes away very quickly.. even before I drive 1/2 a mile. It's almost as if someone hits a button and the hesitation just disappears. After that, it's fine, and it only occurs in the morning on a true cold start. I've read that people have attributed it to the MAFs, an O2 sensor, and have even called it normal, but could this be something due to a faulty cat. converter? I just wanted to get some opinions before I get it taken in for a check. I've also read that a Powerchip upgrade will do the trick, and that's a nice excuse to do it.

Anzir

A bad cat won't make a stumble on a cold start. Most likely causes are coolant temp sensor or possible MAF sensor. What codes did you get from the DME?

Joe

Pete · 14th May 2005, 08:00

Anzir,

I wonder if your severe cold stumbling resembles this:

In the morning, car starts, all seems fine until you put it in first gear. Then as you accelerate the jerky ride comes on , it continues even when you go into second gear, and then stops within a half mile or so of driving. That jerking motion is violent, and almost seems severe enough to damage the engine. It seems particularly bad if you try to step on the gas to overcome it. That about right?

Polynova · 14th May 2005, 08:31

Quote:

Originally Posted by Pete

Anzir,

I wonder if your severe cold stumbling resembles this:

In the morning, car starts, all seems fine until you put it in first gear. Then as you accelerate the jerky ride comes on , it continues even when you go into second gear, and then stops within a half mile or so of driving. That jerking motion is violent, and almost seems severe enough to damage the engine. It seems particularly bad if you try to step on the gas to overcome it. That about right?

I have exactly the same issue, could overcome it with higher rpm /deeper throttling before clutching.

.

ELEVENS · 14th May 2005, 14:24

Mine did that too. Powerchip fixed it.

Polynova · 14th May 2005, 15:28

So you would suspect that it was an electronic control problem?

ELEVENS · 14th May 2005, 20:15

Quote:

Originally Posted by Polynova

So you would suspect that it was an electronic control problem?

My guess is that the factory cold-start mapping is too lean, or the timing is too ******ed, or a combination.

Anzir · 14th May 2005, 22:05

Quote:

Originally Posted by Pete

Anzir,

I wonder if your severe cold stumbling resembles this:

In the morning, car starts, all seems fine until you put it in first gear. Then as you accelerate the jerky ride comes on , it continues even when you go into second gear, and then stops within a half mile or so of driving. That jerking motion is violent, and almost seems severe enough to damage the engine. It seems particularly bad if you try to step on the gas to overcome it. That about right?

The jerking motion isn't too violent, but it once was pretty bad. Yeah, I'm almost scared to try to make it past 3500 RPMs, so I just keep it at 3000 RPM until I'm in 4th, and then it usually goes away by then.

Elevens, if it's the basic cold engine mapping, why wouldn't it be like that from the day I got it? It's very peculiar.

Thanks for your responses, guys.. makes me feel like I'm not really losing my mind. I'm going to clean the MAFs today, but I don't think that'll help much. But at least I'm trying something!!!

Pete · 15th May 2005, 01:19

I wish I could help you guys, but all I can say is that I had the problem, and now I dont. I know its not a normal thing as some have postulated.

The problem was eliminated when BMW did some warranty work on my engine, pretty extensive really. I hadnt mentioned the stumbling at that time, but when I got the car back it was no longer present.

It wouldnt do any good to relate all they did to my engine since it was drastic, and I am sure not all those things were necessary for this particular problem.

Maybe give the powerchip a try, seems to have helped a few overcome this glitch.