starts and idles fine,small misfire at low revs,ok high revs

[wess]

car starts and idles ok,but misfires at low revs then wants to stall on return to idle,but ok when reving high also drives fine,no air leaks new plugs oil and filter air filter new inlet manifold gaskets plus injectors and loom working ok.got car as none runner as fuel pressure reg broke and fuel in engine any ideas cheers 325i

[rallye_turtle]

Could be TPS or ISV perhaps.

[wess]

what are they,where will i find tem,and how do i go about testing

[Bob_S]

any fuel leaks, fuel pump ok?

[wess]

do leaks or smell of fuel don't now a out pump how can you tell going to renew fuel filter soon

[rallye_turtle]

The TPS is the Throttle position sensor, this is connected directly underneath the shaft that the accelerator cable is attached to on the throttle housing, its the little black box which has a 3 pin connector plug on it. This tells the ECU the approx position of the throttle so it can adjust fueling accordingly.


The ISV (Idle stabilisor valve) is the T shaped cylindrical metal device which controls the engine speed at idle, and is situated alongside the almost right angled rubber pipe that connects to the throttle housing.

Cant quite remember how to test these but I'll try and find some info, you will need a multimeter though

[wess]

thanks have got a multimeter might find them in the service book

[j55ura]

wess, any joy with this?? i have exactly the same problems with a slight miss at low revs.

cheers

[mrLEE30]

remove the plug cap from TPS

you will see three pins

set your mulitmeter to read resistance (ohms)

the middle and left pin should have continuity (or 0 ohms) with the throttle closed this should remain like this as you slowly open the throttle until you reach a few mm then it should go open circuit (or infinate ohms)

then check the middle and right pin, the resistance should change as you open the throttle upto the point of about 90% open where you should get continuity or 0 ohms

check this and let us know.


may also be worth checking the blue temp sensor, located towards the front of engine on the thermostat housing.

remove the plug and check resistance accorss the pins, you should have around 2000-2500 ohms when cold and around 250 ohms when engine hot

mrlee

[wess]

I got co 2 tested and needed ajusting on AFM that has made alot of difference now doing rotor arm dizzy cap and leads plus blue and brown temp sensors,done plugs fuel filter plus oil & filter.Also took TPS off and gave it a good clean which has helped to,will let you know what is like when i have done the other bits

[e301988325i]

Split AFM to throttle pipe they often split and cause slight running problems

[mrLEE30]

brown temp sensors

this is only the sender unit to your temp gauge on dash board, blue one tells ECU how hot the engine is

mrlee

[mrLEE30]

note my post incorrect!!

the TPS on these cars do not have the potientiometer part. they only have three settings idle, normal and full throttle. so when you perfrom second part of my test (middle and right pins) the resistance will not change but stay open circuit until you reach about 90% where you will get continuity. i.e the resistance will not change as you open the throttle as i suggested.

mrlee