AFM resistance test

[the_thryll]

I was testing my air flow meter (and other things) to troubleshoot a 1222 code and low-power, engine-dies-under-high-load problem.

How should the resistance between AFM pins 1 and 2 change as you move the AFM internal vane from closed to open? E36 Bentley's explanation is vague: "Resistance should change steadily without interruption."

My readings bounced around a lot, but were ~1200 ohms with AFM vane closed, decreased to ~400 ohms with vane barely open, then increased to ~700 ohms with vane mostly open.

[bmwman91]

The Bentley is wrong. You cannot measure the resistance because, as you noticed, it jumps around a lot. You need to have it hooked up and measure the output voltage, which will vary smoothly as the door is opened. You can put the car into accessory, pull the rubber boot on the connector back and probe the output on the rear of the terminals. The door can be opened by popping the top of the air box open and reaching in.

[d_elson0]

Have you tested the other areas where 1222 comes into play?

[the_thryll]

The Bentley is wrong. You cannot measure the resistance because, as you noticed, it jumps around a lot. You need to have it hooked up and measure the output voltage, which will vary smoothly as the door is opened. You can put the car into accessory, pull the rubber boot on the connector back and probe the output on the rear of the terminals. The door can be opened by popping the top of the air box open and reaching in.

Thanks! Initially I thought mine had issues, but it seems to be fine.

[the_thryll]

Have you tested the other areas where 1222 comes into play?

Car starts and idles perfect. Runs fine if I keep it below 3500 RPM. Go above 3500 RPM and it develops a bad problem: engine runs horrible, car bogs and bucks, exhaust smells awful, CEL temporarily turns on (1222 code), MPG gage drops to below 10. Engine typically dies if I let off the gas pedal. After running rough for 5-15 minutes, the engine idle switches to normal and car runs fine if keep it below 3500 RPM.

I’ve done the following and problem remains:
Checked for air leaks, installed new air boot to TB, new MUTI air hoses, new spark plugs. Heli-coiled all stripped threads for valve-cover bolts, then installed new valve cover gasket set (all pieces). No oil in cylinders above spark plug threads, but tips of two-week old plugs are black already.

Measured resistance of coils and some sensors:
resistance of all coils (pins 1-15) = 0.8 ohms
crank sensor resistance (pins 1-2) = 542 ohms
cam sensor resistance (pins 1-2) = 1278 ohms
tps sensor resistance (pins 1-2) = increases from 1500 ohms (throttle closed) to 4000 ohms (throttle open).

Things to check next:
Fuel-related items
Pressure in cylinders
Source of tiny coolant seep along headgasket under intake.
Other things?