I have a friend with a 1990 740 with Rex/Regina fuel/spark management. He recently replaced the fuel pump because of poor running, which is actually from a failing crank position sensor (CPS).

His idle was erratic, and the throttle misadjusted. The self-test for the IAC did not sound like the healthy Bosch units I've heard, it sounded very slow. He has cleaned it as well, but it isn't idling any better. He needs to pick up the spare CPS I have to progress.


What I'm wondering is has anyone else substituted a Bosch unit (there were 6 in the junkyard last weekend, and 0 Regina) for a Regina IAC? It seems that the ECU controls both in a "live" manner, just like the cruise control does. If the idle needs to go up, the voltage goes up, and if it needs to go down, the voltage goes down. Neither one depends on a set voltage to position relationship, only a differential.

I saw one post that mentioned doing this, but it wasn't definitive or detailed. (https://www.brickboard.com/RWD/index.htm?id=1597299&show_all=1)

Has anyone else tried it? The new Bosch units are about $90-120. The new Regina units are hard to find anywhere (none at FCPgroton or IPD) and in the $275-350 price range. He would gladly spend an hour splicing in a different harness and changing the holder and tubes to have a working idle system again.

Hoping my friend can get his daughter to trust this old tank for her first car, any help appreciated. Her birthday is this weekend.

Happy bricking,
William