HELP - M103 sudden misfiring problem

[BlackBeauty]

Hi guys, this afternoon, after my car had been sitting for like an hour, I fired her up and she started misfiring. Never happened before. After about 3 minutes, the misfiring went off. Back to normal.

After dinner today, the misfiring problem resurfaced. Drove her home and at my car park, I rev'ed the engine and held at 5000rpm for a few seconds and the problem went off. I puzzled...

My entire ignition system is about 1 year old ~ 20000 miles.

* A point to note.. I removed my airbox the other day and broke a small tube that ran from the air box to the fuel pressure regulator. The tube leading OUT from the fuel regulator was also very loose. Not sure if this caused the problem.

Would appreciate any help or input. Thank you.

Rgds