hey everyone, i am having some issues with my engine performance. while driving (never at idle) i have intermittent power loss. the engine RPMs dip down by about 3 or 4 hundred, the lights on the dashboard dim a little bit. it only happens for about one second then it goes back to normal. however it happens in spurts. there will be like 5 to 10 power dips/lights dimming in a row....then nothing.

overall performance is still the same. i can floor the throttle from a red light and the car shoots off like a missile. i only notice the problem when cruising along at regular speeds or highway speeds.

my car has the following specs (im not sure if it will help diagnose the problem):

• 2004 545i w/ 51k miles
• Dinan Stage 3 software
• Dinan dual cold air intake (RPI scoops)
• Supersprint Exhaust
• i have been running 87 octane here and there but the last two full tanks were 93 octane

my check engine light came on about three weeks ago for 'Increased Emmissions' im sure this has something to do with it. I can only guess that its an O2 sensor, an engine coil going bad or perhaps a vacuum hose going bad or loose.

please help!

 

I would say a bad vacuum hose or coil can reduce engine performance no? But I would get that alternator and battery tested it could be sudden dips or spikes in power. Just throwing stuff out there, maybe someone with more knowledge can chime in

 

I had the same issue when my alternator needed replacement.

 

although I'd investigate the check engine light, the only thing that would cause the lights to dim is the alternator. a Bad O2 sensor wouldn't do that, nor would a bad coil (you'd have some rough running all the time if that were the case) and a vacuum hose leak wouldn't affect the lights either. your battery could be shorting out, too.

 

I'm wondering if it is gas, I got a bad load and it acted exactly like you did and after putting a bottle of techron in and running three good tanks of chevron it is slowly getting better.

 

Voltage regulator [attached to the alternator] would be my guess.