Need HELP! 04 M45

[BLKTOPS14SR]

I have a 2004 M45. I've owned the car for 2 weeks. Ran and drove really good, just needing normal maintenance. It has 144k miles on it and 100% stock. The other day while at a stop light it suddenly died. Was hard to start and after had little power and wouldn't rev past 4k rpm. It bucks and studders badly. Changed plugs, cleaned maf (with maf cleaner) and new air filter. Any ideas what its problem is? I've read on here and multiple others sites that it could be bad maf, TPS, Cam sensor, fuel pump, catalytic convertors and etc. I'd hate to drag this car across the scales if I cannot fix it within a reasonable amount of time and little money.

[Double E]

Assuming all was unchanged before the problem, sounds like the cam and/or crank sensor. Common issue & easy to DIY. Get the OEM replacement. I've not seen a fuel pump go bad on these yet. If it's the converters, it's probably also rattling pretty bad from the bottom of the engine.
Important question...did you do the maintenance (plugs, clean MAF, etc..) before or after the issue?
If it was done before, the MAF needs to have the re-learn procedure done and it should be fine.

Please also describe the procedure you used to clean the MAF...

[BLKTOPS14SR]

I did the plugs and Maf after. The maf was already off to do the driver side plugs. I used CRC MAF cleaner. Sprayed alittle on the sensor and let it air dry. Spray some on rag to wipe off residue inside the MAF. Also cleaned inside the tb. I've heard these have issues with the Camshaft sensor. I'll look to get them and replace them. I seen the real nice stickie on resetting the ECM and other sensors relearning. I hope that's all it needs. Before this it ran and drove great. I have noticed though the power steering is now really stiff after it did this issue.

[Double E]

If you did not disconnect the battery before doing all of this and also opened the butterfly valve, it needs the reset.

The manual reset procedure is difficult at best. I've only been able to do it once successfully. The dealer can do it in a few minutes with the Consult tool. Just tell them what you did and they'll know what it needs. Beware though, some service writers assume the consumer has no idea what they are doing and will want to run a full diagnostic procedure on it to be certain of what's wrong before taking what you tell them to do and just doing it. In actuality, they are partially correct as you should have disconnected the battery and/or not moved the butterfly valve in the process. One may not think it's possible to clean without opening it but it is possible with some toothpicks and the cleaner you used.

If they charge an hour labor, you're still ahead as the plug change alone on this car is nearly $500.