M30 - rough idle and poor fuelling at tiny throttle openings

Mon Jan 31, 2011 12:55 pm

Afternoon all,

I have a couple of reasonably minor issues with my M30'd cabby ('91 E32 735i motor with EML fly by wire throttle, catalyst engine with the lambda sensor disconnected), I am struggling to solve them.

- Idle is rough, jerky even, almost as if it is misfiring. Never stalls, tacho is rock solid at about 700rpm, just does not idle smoothly. Always feels like the ECU is struggling to maintain idle.

- Fuelling at tiny throttle openings is poor. It is impossible to maintain 20mph in 2nd on the flat for example, car hunts and jerks at such small throttle openings.

It has done this for the 2+ years I have owned the car, but the small throttle fuelling is worse since Fritz's fitted their chip and a manual box for me. Perhaps it is the chip, perhaps the old torque converter masked it. Car recently made 249hp on the dyno, so my feeling is that the engine is mechanically sound.

Any thoughts? I have checked for vacuum leaks in the inlet tract, both visually and by spraying brake cleaner everywhere whilst the engine idles.
Also tried plugging the lambda sensor back in, barely runs at all when connected.

Cheers all,

Martin

Fri Feb 11, 2011 5:33 pm

3 things to test/check

is the crank sensor wire chafing on front pulley ??? check it as even the outer sheid making contact will cause interesting and annoying running issues, VV common on M30

check the TPS, if its set "tight" you can trigger it on small openeings and cause massive lean bucking and al you described.

easy enough to sort on M30.

alternative assuming the TPS is 100% check the idle mixture, if its lean lean then it will remain lean until around 2.2K hence the poor on/off transients you're suffering.

HTH,

Sat Feb 12, 2011 8:55 pm

Thank you so much Ant.

I have some learning to do before I can even think of attacking your second and third suggestions, but I will.

Martin.

Sat Feb 12, 2011 11:54 pm

Ive been waiting for an answer to this thread as the M30 ive just pulled out has similar idle problems to yours, but like you i checked for air leaks etc with no joy.

This

Ant wrote:is the crank sensor wire chafing on front pulley ??? check it as even the outer sheid making contact will cause interesting and annoying running issues, VV common on M30

On checking the engine that i pulled out i found the crank sensor was actually touching the pulley to the point where it was marking the sheild. Worth a look, im not sure what the gap is meant to be between them though.

Tue Mar 08, 2011 5:38 pm

A bit off topic but how did you manage to get 249 bhp out of a m30?

Thu Mar 10, 2011 10:24 am

noclue wrote:A bit off topic but how did you manage to get 249 bhp out of a m30?

Full BTB exhaust including 6 branch, Fritz Bits chip, fresh injectors/plugs/airbox etc, and probably a fairly generous correction factor on the dyno

Martin.

Sun May 01, 2011 12:11 am

Did you sort this out?

Mon May 02, 2011 9:56 am

No, not yet. I looked at the crank sensor wiring and proved that it is not chafed, but have not got round to testing the TPS.

Mine is also missing the inductive sensor that wraps around HT lead number 1, so I am searching for a decent used #1 HT lead and sensor first.

Martin.

Mon May 02, 2011 10:13 am

The crank sensor should read 540 ohms +/-10% worth checking as a friends M30 was running like a bag of nails, cable looked undamaged but was reading around 490 ohms. New one fitted and viola - ran perfectly.

You may find the No1 lead from an M20 set will work, may open up the market a bit.

Charlie