Does anyone have any suggestions about why my 530 idles rougher the warmer the engine gets(or more miles traveled)?
Do you have the updated Alusil engine block or the dreaded Nikasil block? If you have the latter, then you are experiencing the early symptoms of premature Nikasil block wear.......
The ICV/idle control valve might be at issue or you might have a vacuum leak from your gaskets. Any decent bmw indy mechanic will be able to diag and repair it in a jiffy. Either way, it won't be expensive. Just old age makes gaskets degrade, and the ICV fails after a decade.
In general, I have not encountered a Nikasil problem on a V8 that has lived this long. Usually rough idle is caused by a vacuum leak at the intake gaskets or the breather/separator. The reason it gets worse as it gets warmer is that when cold it runs richer and that may be enough extra fuel to cope with the leak. As it warms up the normal program is to run it pretty lean and any extra air makes it run rough. If you keep going like this, eventually the check engine light will come on, but it will either be a deceptive O2 sensor code, or a mixture code (usually the former.) The fix is not cheap, and there are a few things you really ought to do when you fix this. Start with resealing the valley pan, replacing all the knock sensors (they are usually done in by heat at this age) replacing the water pump if it has not been done, or removing the coolant tube at the back of the heads and resealing that if the pump has been done in the last 50k miles, then the intake gaskets and the breather separator. If you are not interested in doing all of this (or simply can't afford it at the moment) have a shop smoke test the intake to find the leak. If it is just the breather plate at the back of the intake, that can be done on the car (by a clever mechanic) and you will be OK for a while. If it is the intake gaskets, that can be done fairly cheaply, but remember that other stuff lingering under the manifold. Go to a good independent shop, not the dealer. Make sure the shop has a good scan tool (Autologic or Launch X431 infinite) and a smoke machine to test the intake. Good luck.
