BMW Repair: 1987 325i will not accelerate, air flow meter, o2 sensors

Question
Josh,
Wonder if you have any ideas on this one... I'll explain the issue and list what I've done so far.

1987 325i
Problem:
- Runs poorly. Idles "ok" Have to feather it until it warms up a little. Even then it 'searches'.

- Seems to be running rich (rich enough that I had to replace the plugs to get it to fire.)

- Seems like the engine will simply not accelerate past 2000 r's (approx)

- backfires as soon as the throttle is pressed. (If I start it with the TPS disconnected it does this right away.)

- smokes when it's accelerated. (this is why is seems to me it's running rich.)

What I've done:
- Replaced MAF with a used/working unit
- Replaced Motronic with a used/working unit
- checked all sensors with ohm meter. All seem to check out against the specs.
- ohm'd out each wire between all sensors/injectors and Motronic
- Replaced Plugs
- A shop replaced the FPRegular.
- Compression test. OK on all 6 cyl. (Not leak-down test, yet)
- fuel pressure test. OK based on spec. (Need to do this again to ensure the FPR is not for an E.)


I think that's it so far. I'd love to have your input.

Thanks
Brad Yoder
Amana, IA

Answer
Brad,
 It seems as if you know what you are doing, but this does sound like a TPS issue or the MAF (Air Flow Meter) may not have been a good one that you swapped in.  However did you notice any change at all with the parts you swapped?  If nothing changed, and the car runs the same, I would look at the Throttle Position Switch.  I'm sure you know where it is, since you pointed out that you unplugged it.  It is just a black box with two pins inside.  When the car is idleing it should be touching the idle contact.  As soon as the throttle is cracked you should not be in contact with this idle pin.  There is also another pin for wide open throttle (WOT).  At WOT the pin should be in full contact, and the ECU will go into WOT mode.  WOT mode ignores inputs from the O2 sensors, and tells the injectors to squirt as much fuel as possible (sometimes causes black smoke in the exhaust).

 If you are seeing black smoke (not to be mistaken with black/blue smoke which is oil) something is telling the injectors to squirt too much fuel.  If the FPR was for an "e" car, it would allow less fuel pressure than the "i", so I dont think that's the problem.  

 I personally think it's the TPS, either it's bad or out of adjustment.  Check out this link:

 http://www.bmwe30.net/cgi-bin/datacgi/database.cgi?file=articles&report=view&ID=...

 Good luck Brad,
 Josh