'93 318i dies on acceleration

[Dingo76]

It starts well and idles ok. Thru most driving conditions it runs well..but accelerating from a stop causes it to bog or stall...i really have to get rpms up to get thru that stage

any suggestions welcome

[bmwman91]

Is the issue related to vehicle speed, or engine RPM?

If it is RPM-related:
Change the fuel filter and maybe see about getting the injectors cleaned.

Is the original catalytic converter in there still? Although rare, it can fracture and block the exhaust.

There could be wear in the air flow sensor which will cause the ECU to cut fuel.

Dying ignition coils can also cause stuff like this.

[Gregs///M]

Vaccum leak, CPS or AFM.

[Dingo76]

Ign off, harness connected... I measure between 1 and 2 on AFM: 11.2k ohms...as I move the vane from air filter end, I get no change in reading...

[Gregs///M]

Ign off, harness connected... I measure between 1 and 2 on AFM: 11.2k ohms...as I move the vane from air filter end, I get no change in reading...

Cant use a meter to measure the AFM output. Meters take and display an average so when you are measuring it with a meter, you are actually looking at the average resistance. You can only use an oscilloscope while installed on the car or a 5v power supply. See my AFM thread for more info about how to properly test and AFM. But honest, Ive rebuilt many thousands of AFMs and never once seen one enter our shop that was consider "still good" after 30+ years.

[bmwman91]

The AFM is not "just" a potentiometer, so as noted a resistance test means nothing. You will see the value fluctuate up and down as the vane opens due to how Bosch laser trimmed the carbon track and its pull-up taps. You need to put the car into accessory mode, have the AFM plugged in, pull the boot back and measure voltage across pins 2 (output) and 5 (ground). It should rise smoothly from ~0.27V to ~4.8V as you manually open the flap by hand. If there are skips or drops along the way, then the track is worn.

[Dingo76]

Thanks bmwman .. will check that.

meanwhile engine code 1222

with Vac guage attached: warm start.. it idles st rock steady 18 for 5 mins or do, then at some point starts dropping steadily to 12 psi very rocky idle . Then 3 mind later it goes right back to 18... then a few mins later back to 12