E34 M20 with Hesitation on Acceleration

[lmoser@xxxxxxxxxxxx]

I have a 1990 525i, E34 with the M20 engine (same as 87-91 325i) with
209k miles. When warm, the engine hesitates on acceleration, mainly from
a stop and exhibits a rough idle that occasion will stall. It also takes
longer to start sometimes, cold or hot. The problem is worst when
accelerating from a stop and idling while stopped. I have to put the car
in N to avoid it stalling. Sometimes you can also feel the hesitation
under mid range acceleration.

Here what we have done so far:

New spark plugs (Bosch copper)
New spark plug wires, cap & rotor
Replace O2 sensor
Check for vacuum leaks
Fuel pressure is good
Throttle position sensor has been checked

The problem has gotten worst in the past 3-4 months. I use 89 octane
fuel and occasional use Techtron fuel additive. At this point, I do not
know if it's a spark or fuel problem. The plugs indicate that the engine
is running rich on all cylinders.

If anyone has any thoughts, please e-mail them to me. I don't know what
else to do.

Thanks,

Link Moser
1990 525i 209k
Loudon, NH

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