97 318i knackered air boot now won't start

I been trying to help a friend with his 318i and it had a knacker inlet
duct leaking air after the air meter.  This was fixed for a few weeks
with tape and the engine problems have returned, but now it won't start
even with a new boot.

Before getting worse it was reving up and down, and then wouldn't run. I
did try and start it yesterday and it ran for a bit (badly) and I
suspected the tape was not sealing it.  Now it won't start atall.

I havn't seen the car since he's replaced the duct and he says the
battery is still ok, so maybe he hasn't been trying hard enough.  He
also says the rev counter is jumping around when he is trying to start it.

Should I keep trying or is it likely there is another fault?  Flywheel
sensor?

--
Tony