2001 BMW 525i cold starts

WALKERGANG

MEMBER
2001 BMW 525I
6 CYL
2WD
AUTOMATIC
12,200 MILES

Last year on cold mornings my 525 would idle roughly for a few seconds, then smooth out. It didn't do it during the summer. Now that it is cold again, the problem returned, only worse. The starts are extremely rough. Car barely idles without me giving it quite a bit of gas. After about 15 seconds, I can turn the car off and immediately back on, and it is fine. If it sits all day, it will have another rough start after cooling off, but not nearly as bad as in the mornings.

5 Replies

DOCHAGERTY

MECHANIC
9,601 POSTS

There seems to be something temperature related, has the cyclone separator ever been replaced?

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Thursday, October 15th, 2009 AT 11:01 PM

WALKERGANG

MEMBER
3 POSTS

The dealership replaced what they called the vapor separator last week (is that the same thing?)With aboslutely no change in performance. The technician told me late yesterday he is suspecting a blown head gasket. Coolant is leaking into the cyclinders causing the misfire in the mornings and after long periods of sitting. Then is burns out. Seems logical, but I don't know why the problem would go away immediately after just turning the car off and on quickly while it is stuttering.

A non-BMW mechanic was thinking there is an electronic solution - sensor, fuel control module, etc.

Any other thoughts?

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Friday, October 16th, 2009 AT 8:49 AM

DOCHAGERTY

MECHANIC
9,601 POSTS

The failed head gasket scenario doesn't play, if it were the issue you would have more of a steam out the tail pipe and loss of coolant type of thing going on. If I am wrong about the gasket, then the casting could be cracked. These are worst case and I don't like the worst case for engines that have not been overheated, ever. BTW, have you or has the engine ever been overheated? To your knowledge? A sensor or module would command the check engine light on, if there were a failure. If there is coolant in the combustion chambers, a peek into each of the cylinders with a bore scope might aid this diagnostic, look for cylinders that have been washed clean, at 122k miles there should be some carbon build up.

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Saturday, October 17th, 2009 AT 10:14 AM

WALKERGANG

MEMBER
3 POSTS

The thermostat went bad this summer and the car did overheat, but I left that detail out since the problem started last winter before that happened. After replacing the thermostat and radiator this summer they told me the engine had no damage due to the overheating. That was in June and the starting problem didn't start happening again until it got cold, just as it did last winter.

The bore scope is a good idea - I don't know if that has been performed or not. I'll ask them if they can do that.

Thank you for all you help and time.

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Saturday, October 17th, 2009 AT 10:33 AM

DOCHAGERTY