BMW 4.6 is poor acceleration and hesitation

[bcredliner]

Bad cat will cause will throw weird engine codes. The previous bad coils were likely not burning the fuel, if they were even bad, which would contribute to a cat fail. Cats will rattle when they are shot and will be intermittent. Trace the rattle to the source. Bad cat restricts exhaust so engine will only rev so high as the engine can't suck in more air because it isn't getting out.

If they say a coil(s) are shot I would ask that they test the coils by moving a good one around and see if the faults move to other cylinders before buying new coils. I do like to change all the coils when one goes bad--but I am one that never wants to risk losing any amount of performance.

Now that it is missing at idle it should be easier to pinpoint the cause

As per Pezho and Aman

[Aman]

Originally Posted by bcredliner

Bad cat will cause will throw weird engine codes. The previous bad coils were likely not burning the fuel, if they were even bad, which would contribute to a cat fail. Cats will rattle when they are shot and will be intermittent. Trace the rattle to the source. Bad cat restricts exhaust so engine will only rev so high as the engine can't suck in more air because it isn't getting out.

If they say a coil(s) are shot I would ask that they test the coils by moving a good one around and see if the faults move to other cylinders before buying new coils. I do like to change all the coils when one goes bad--but I am one that never wants to risk losing any amount of performance.

Now that it is missing at idle it should be easier to pinpoint the cause

As per Pezho and Aman

Thanks for your help
After I took the car to the garage again today they reset the engine management light
Now when the car idles there is no misfire again
It seems me making the car go to 4000 rpm causes a misfire at approx rpm, if I do it enough times the EML stays on and the misfire stays, until the EML is reset... so it seems...

[bcredliner]

Originally Posted by Aman

Thanks for your help
After I took the car to the garage again today they reset the engine management light
Now when the car idles there is no misfire again
It seems me making the car go to 4000 rpm causes a misfire at approx rpm, if I do it enough times the EML stays on and the misfire stays, until the EML is reset... so it seems...

Your are correct, it will come back because the the computer will get the same signals that caused the EML to come on previously.

Are you still at the shop or is that all the shop did?

[Aman]

Originally Posted by bcredliner

Your are correct, it will come back because the the computer will get the same signals that caused the EML to come on previously.

Are you still at the shop or is that all the shop did?

That's all the shop did as they were only open half day
They didnt charge me though!
Should I take my car back to the BMW specialist and let them investigate or just go to an exhaust place and get the cats looked at?