What could this problem be?

[adrean8j]

As most of you know I have a 1999 5er with the M52TU engine. Right now it cold starts horribly and the check engine light is on. Over the past 3months I have replaced the ABS Computer(Brand new), VANOS(Brand new), Camshafts(Schrick Sport Cams), and Oil/Oil Filter. Took it to the "stealer" and they ran the codes(for free) and it said an "intermittant spark plug failure....ALL 6!!! So I promptly went out and bought brand new plugs directly from Bosch and replaced them...cars seems to be running a bit better and no engine light(BMW had reset it for me). Yesterday the check engine light came on AGAIN.....my exhaust note seems to be a lot deeper and pronounced of late...soo I am thinking that there is a potential hole somewhere in my exhaust setup....would that cause me to run rough and have a check engine light? I currently use 100 octane fuel but I seem to have lost a little bit of power in the low end and the engine just doesnt seem to running smoothly....

 

[epj3]

Could they be getting fouled? Take one out and check to see if its a weird color. Could be bad O2 sensors too! I'm new to this whole "OBD2 thing" so they are just guesses.

 

[adrean8j]

Could they be getting fouled? Take one out and check to see if its a weird color. Could be bad O2 sensors too! I'm new to this whole "OBD2 thing" so they are just guesses.

When I changed them last week a couple of them were actually loose to the point where i didnt have to break the "seal" to unscrew them or a better way to describe it as being "hand-tight". But they are replaced now by myself so I know they are torqued right. The old plugs were dark and ummm....fireburned??? that is on the side where they fire from......

Where exactly are the O2 sensors on the M52 engine? To be honest I dont even know what those look like....

 

[epj3]

When I changed them last week a couple of them were actually loose to the point where i didnt have to break the "seal" to unscrew them or a better way to describe it as being "hand-tight". But they are replaced now by myself so I know they are torqued right. The old plugs were dark and ummm....fireburned??? that is on the side where they fire from......

Where exactly are the O2 sensors on the M52 engine? To be honest I dont even know what those look like....

There are two before the cats, and two after the cats.