Car Is jerking

[daddy007]

I have a bmw 325i 1990 motorsport

[BristolE30]

I have a bmw 325i 1990 when the car is cold it starts jerking and jumping once your pull off but as soon as the car is warm its totally fine
im getting loads of different opinions but no seems to kno exact

the car does have big cams where the idle is all over the place but im sure that is not the cause cause otherwise it would do it everytime, its had a tune up and stuff but made no difference

Is it jerking under only light throttle? Or wide open also?

[daddy007]

only light throttle, if i step on it hard its fine

[paultv]

Mine does this too with a feathered throttle in first when cold...made it better setting the idle mixture a bit richer but it still does it...you can coerce it to kangeroo quite badly on occasion, but it only does it for a short while...when cold.

Running everything standard right now.

I often think the AFM flap "delay" might be responsible, getting into some kind of oscillation? As it almost feels mechanical.

Paul

[daddy007]

yeah spot on feels a bit worser than a kangeroo my one, i had it all tuned up like set the idle etc etc everything is spot on but still have the probs, been told loads of things like gearbox, diff, air leak, air flow meter, mounts etc etc don't know where to start

[BristolE30]

Mine is the same. Think a lot of E30’s suffer this. I’ve not found a cure yet

[coopman]

Mine's always a little jerky in first - fixing various vacuum leaks has improved it a lot. I've also kind of got used to it - there's a knack to coming on/off the throttle with mine.

[daddy007]

i honstly dont kno where to start, even finding a right mechanic is a mission, really need some e30 specialist that knows these cars inside/out

[paultv]

My mrs. used to drive her mums 325i cabby in the 90's which was new, here in Germany....black with champagne leather, and she says it was exactly the same...I believe it's the butterfly / AFM flap getting into some kind of oscillation, and maybe one of the reasons why the system was dumped in favour of the simpler and more reliable MAF..

I wonder if the damping in the flap becomes weaker with age....or possibly "sticky" when cold or is the air teperature thermister in the AFM intake out of spec?

Paul

[daddy007]

took my car to the garage was told it was a slight air leak coming from exhaust also the afm screw or somthing was screwed right in and it should be loose for air to go past also car was running quite rich, had it all fixed and 60% of the problem of jerking has been solved still have slight jerk but not as much and bad as before so i think i will need a afm to cure this 100%.
paultv i mite well be right

[ah]

Mine does the the same hot or cold,3 or 4 macanics changed and bought so many things, and 10 years later still the same.I need to book an appointment with Barry BBS325i BMR performance.

[daddy007]

do let me kno what BMR says, thing is that they are quite far from me so cant really take the car there.

[jmec]

Mine's the same. Leaving the house when cold I have to power up a hill and all is well. Coming down the other side on light throttle and it's developed hiccups. I just dip the clutch. Always been the same in 8 years of ownership.

[paultv]

Thought I'd revive this old thread...after the very nice technician at Poulton Test Centre in Dover allowed me to adjust the idle CO on his gas tester...this little quirk has gone. Initial reading was 4.1 CO which is crazy rich...this I'd set by adjusting the idle air to the factory value stamped on the AFM.

I had to weaken the mixture a lot to arrive at a CO of 1.0 ( m20b25 should be 0.8 - 1.0 )

So just a heads up...get your idle mixture set correctly then don't fiddle with it...assuming of course you have no other air leaks.

Car does not display the feather pedal kangeroo when cold now.

Paul

[twenty]

Good to know. Luckily for me, I’ve never had to witness this despite the car almost hitting 160k miles.

[BristolE30]

Thought I'd revive this old thread...after the very nice technician at Poulton Test Centre in Dover allowed me to adjust the idle CO on his gas tester...this little quirk has gone. Initial reading was 4.1 CO which is crazy rich...this I'd set by adjusting the idle air to the factory value stamped on the AFM.

I had to weaken the mixture a lot to arrive at a CO of 1.0 ( m20b25 should be 0.8 - 1.0 )

So just a heads up...get your idle mixture set correctly then don't fiddle with it...assuming of course you have no other air leaks.

Car does not display the feather pedal kangeroo when cold now.

Paul

This is very interesting

[ah]

Why this is,I haven’t the faintest but mine always does it worse in reverse.Does anyones car on this post suffer with reving it then the revs drop and it briefly try’s to stool itself and then the revs rise again.(m20)

[BenHar]

Why this is,I haven’t the faintest but mine always does it worse in reverse.Does anyones car on this post suffer with reving it then the revs drop and it briefly try’s to stool itself and then the revs rise again.(m20)

Could be air leaks, but I would check that the TPS is set correctly as a first point of call.

Ben

[onthames]

Mine kangaroos a bit in traffic sometimes. Seems to happen randomly and happens at very low speed in 1st gear.. maybe not adding enough throttle, who knows.

[jmec]

Mine's the same when cold, 325i cab. Same with my e36 328i coupe on the same route; up hill from the house they're fine. Down the other side of the hill they will jerk if I don't dip the clutch. Doesn't last long so I live with it.