e30 m20b20 wont start

[Brianmoooore]

i've now spent as much as i paid for the car on new parts for it

That's because you keep replacing rather than testing!

[Barton]

its my choice though isn't it? i come on here, i search through forums, and yet no-one has a fool-proof way of testing this fault

if i check fuel pressure and its fine, then what?

[Grrrmachine]

one of the other two; air or spark. If the car is managing to run eventually, it suggests that you're getting all three into the engine, just not in the right quantities at startup.

Put the old parts back in (so that you know the new parts haven't introduced new problems; as Brian stated previously, that can happen), get your multimeter out, and find out what readings your Throttle Position Switch and Air Flow Meter are giving you (search the Tech section to find what they SHOULD be.) Spray some carb cleaner around the inlet side of the throttle (all rubber hoses) to see if you've got a small air leak. Take off the throttle body and make sure the small rubber blanking plug on the back (to the deleted Carbon Canister) hasn't rotted away. Take the distributor cap off and see if the rotor is in good condition. Suck on the Fuel Pressure Regulator to see if you get petrol in your mouth (meaning a split membrane.) Take off the earth straps and clean up the connections.

Basically, there's plenty of things that can be checked in 5 minutes, for free, that could have been the problem before you forked out for parts you didn't need.

[Barton]

its got new cap, rotor, plugs for the ignition side

fueling: pump, reg, hoses, filter

have replaced the inlet hose, and the air filter, checking the vacuum hoses as well for leaks

the problem was there before and after

problem is that its intermittent, if it was a problem every time i tried to start the car, it might be easier to locate

[Brianmoooore]

These are very, very simple engines. If it is injecting fuel at approximately the right mixture strength, produces sparks at roughly the right time, and has reasonable compression, then it will run.
One simple sensor controls both the spark timing, the fuel pump and the injectors.
It's your choice to throw whatever new parts at it that you fancy, but in doing so, and disturbing things that didn't need to be replaced, you run a very real risk of introducing faults that you didn't have before, and making fault finding very difficult, especially when you're no where near the engine and have to rely on second hand tests.
That is why you test, and don't replace, until you are as certain as you can be that you know exactly what the fault is.

[parkin10]

once the engine has run will it start up properly straight away hot or cold?
mine has poor start up probs like yours
be interested to see what you find

[Barton]

no, the fault is completely random, hot or cold it will fire up on the button or it will turn over a good few times before finally just catching

[parkin10]

brian says test before replace he`s right
but i have had this car 4 years and i have never been happy with its start up
so i have started to replace parts on the engine
fuel pump+filter
fuel rail pressure reg
injectors cleaned by ultra sound
cps
distributor cap+rotor arm
leads+cam postion sensor
plugs
coil
changed air flow meter (not new)
changed ecu (not new)
no air leaks
tps works
once running goes ok
no more ideas

[Barton]

hmm, sounds like i wont get to the bottom of the problem then

[BadMoonRising]

I had starting problems with my 320i.

It was the Temp Sensor.