535i ecu malfunction?

[gt90]

I have 2 questions I need some insight on.
1.) I need to know if I can use an auto 535i ecu (the whole motronic ecu) from a 1990 auto in my '89 5 speed?
They have the same numbers (0 261 200 179).
I need it because mine is apparently shot.
2.) When I "goose" the throttle in neutral the rpm's drop or stay the same for a split second before shooting up, sometimes on a hill if I have to start quickly the car will stall.
I had my mechanic check it out and he said that the voltage at the TPS was 12 volts when it should be 5, and that at some points it was "all over the place", he said to try another ecu. Could this be the problem?
Thanks for any help.
*edit*
I switched out my chip with my old stock chip from my '90 auto and the car seems to be less hesitant and has regained some of that famous m30 low end torque but it still feels lacking.
So I guess I answered my 1st question myself.
I am still interested in whether my erratic voltages being sent to my TPS point to a motronic malfunction.
Thanks for any help:D

[shogun]

If it has the same number, you can change it out. But I wonder if this solves your problem.

[gale]

As Shogun said, as long as it's a -179 you can swap an auto DME into a manual, and a manual DME into an auto. The only problem with using an auto DME in a manual is the idle speed will fluctuate. You can correct that by using an aftermarket performance chip such as Mark's EAT chip.

Did you have a performance chip in it before you put the stock chip back in it? I have noticed an improvement with various performance chips in mine but the lack of performance is more dramatic when going back to the stock chip after having gotten used to the performance chip.

You could try ebay or Vines for another ECU, they sell for as low as $40 for a good used one & that way you'd always have a spare if it turns out that isn't the problem. Also, have you checked that the alternator is putting out a clean 13.8V +/- signal? When the brushes/regulator craps out, voltage will be all over the map & can really create havoc.

[SRR2]

The voltage to the TPS doesn't sound right, but you might want to check that out for yourself. I'm a bit skeptical that the ECU would work at all if that 5V supply was wandering all over like that.

The problem you describe sounds more like a bad AFM. With a manual trans and that kind of mileage, that AFM has seen a whole lot of cycles. They are mechanical abominations and don't last forever. I just replaced the one on my iX that has about the same usage as yours. It was shot. The element had obvious wear on it, and the wiper was worn.

If I were you, I'd just replace the TPS. That's had a lot of wear too, and they don't last forever either. A faulty TPS can produce all kinds of strange idle-related problems. The one on my 535 failed at 115K. It was a biatch to troubleshoot because the switch closed intermittently and unpredictably. It would work when cold, but fail more frequently as it warmed up.

Aren't old cars fun.

[bill g]

I am not sure the supply voltage to the TPS should be 5 volts on the 535. On my 1989 535 manual it is around 12 volts and there have never been any driveability or performance problems with it.
Circuit diagrams I have seen show 5 volts but I am thinking this is a mistake. There are good reasons for using 5 volts on the throttle position sensor on a M50 525 for example, which is a potentiometer returning a varying signal to the ECU.
The E34 M30 535 TPS is actually a throttle position switch ie. it just has a couple of sets of contacts which sense on/off so the actual voltage may not be important. The signals it returns to the ECU are either a voltage, or no voltage.
I would really like to get clarifaction on this - maybe some other guys with 535 could check voltage supplied to their TPS.
I agree you should check the air flow meter - the thing has moving parts that are more likely to wear and give trouble than the ECU.

Bill G

[gt90]

Gale - I don't think the alternators bad because there are no other signs of it going, I have a pretty powerful audio system and it doesn't dim the interior or exterior lights at all. And the car always cranks strongly when starting.

Since I bought the 535im it had the stock ecu in it, but when I first got it it pulled noticeably harder than it does now.
I also forgot to mention that after disconnecting sensors the CEL never came on. I know the bulb works because I have done the stomp test before, and it lights up a few seconds every time I start the car
Could this be a sign of a bad ecu?

[gt90]

bump for help?