Engine Miss R50-'02
 

I have been fighting an engine miss for about a year now. It can begin to miss while idling at a stop sign, in between shifts or it can even start to miss while I am driving at a steady speed. I changed out the coil pack, wires & plugs. I put it on my code reader and changed everything it said to change plus I changed a few other parts while I was at it. Nothing cured it. I brought it in to a garage, they experienced it and gave it a leakdown test. They said it was probably the cylinder head (bad valves). I pulled the head out, had it redone with new valves and still no change. I have called the dealer and asked about a reflash on the cpu. The price per half hour was high, so I said, "how long does it take" they replied that they didn't know. I am not about to bring it in and give them a blank check.
Has anyone had this problem and did you get it cured?

I forgot to add, I can make it go away by either shutting the engine off while I am driving it ( not so good at night )and then restarting it or.. by downshifting it and letting the car drive the engine a bit.

have you tried fuel treatments/cleaning the injectors ? a clogged injector can cause a miss as well

Yes, I have done that.

Fuel Filter ? Fuel Pump ?

A DME "reflash" is not going to fix your problem, its only going to make it temporarily go away...if that.All it would do is reset your adaption values... fuel trim,spark extc.
You need to start by smoke testing the intake.Best way (on Cooper S) is to remove
map sensor and pump the smoke in that way.You really want to be 100% sure there are no vacumm leaks.Its not always going to show when pulling up codes. Note: "reflashing" the DME aka resetting adaption values takes 10 min at the very most, just so you know.However, the dealership, in there own right, is going to charge .5 to 1.0 hrs, maby even more .

I "tested" it by unhooking it at the engine and pumping fuel out. It seems to work just fine. I have not replaced any injectors though. The trouble codes always say it's #2 and/or #3 cyl miss.

Thanks for the info on the reflash. I have replaced all the gaskets since I did pull the head and sent it in for a valve job. So all the gaskets are new. Not sure where to go from here.