few pointers please

[greg320i]

hi newbie here,just bought a 320i nice car however i have a slight hesitation when tapping the throttle from idle,it drops the revs and wants to cut out,now the previous owner has replaced a few bits to my knowledge,he never told me but on inspection,i found an old idle control valve in the boot,so a new one has been fitted also fuel press reg,new ecu has been replaced,it has a pipercross filter on aswell

question is where do i start,i work on tuned cars but some obvious pointers would be welcoming,my understanding is a leak between manifold and filter,im going to remove intake manifold and check for any vac leaks,anyone know what the tps should read at idle and at full WOW

thanks in advance,il post a pic of motor and hopefully get a bit involved with the club

cheers greg

[BMW_YARD]

Check the throttle idle switch.

Most muppets usually adjust this to 'mask' other problems they can't fix, and somebody has been around the idle control on this car.

Basic check is to listen in the area of the throttle body when you make the first movement of the throttle.

Poor starting and dying can be caused by the DME not recognising the idle position.

Although the throttle idle position screw shouldn't need to be adjusted.

[greg320i]

Check the throttle idle switch.

Most muppets usually adjust this to 'mask' other problems they can't fix, and somebody has been around the idle control on this car.

Basic check is to listen in the area of the throttle body when you make the first movement of the throttle.

Poor starting and dying can be caused by the DME not recognising the idle position.

Although the throttle idle position screw shouldn't need to be adjusted.

throttle idle switch is that the same as throttle position sensor TPS?
just checked manual and it gives values of 5volts at idle from the throttle side!

dme?wheres this matey and how to check etc

thanks greg

[BMW_YARD]

On a manual gearbox car the BM doesn't exactly have what you'd call a TPS, on the 320 manual the throttle switch will only switch for two positions, at idle, and at full load, anything in between is not sensed.

On an auto it is more of a TPS, whereby the base voltage is returned to the DME as a variable signal, through the full range of throttle movement.

DME is Digital Motor Electronics (Street speak for engine management).

.......i work on tuned cars.......

It might help if you explain what level of previous knowledge you have?

[greg320i]

well throttle switch seems to be fine,continuity on pins in open and closed position,still has same hesitation when tapping throttle,but is fine on the move.only audible noise i get is you can hear the filter sucking then the revs drop off

will ajusting the tappet clearances prove to be an improvement,i also noticed a slight noise coming from the rocker cover more noticable at around 2500rpm,sounds similar to when you touch a plastic fan blade whilt moving is the best way i can explain scraping type noise.

sorry to go on,just need to clear up the niggles,perhaps im to fussy but i like to have the car running sweet

greg