bad trans causes high idle?

[htown318is]

have an auto 89 325i, did all kinds of tune ups with filters, pump valve adjust etc. fixed my cold start issue, problem now is soon as I turn it on, it jumps around 1200-1500 in P, N D 321.

when i put it in R, it goes back to normal 700 rpm. only R works on this trans. there are no functioning forward gears.

kinda confusing, is there a sensor of some sort in the trans or computer that triggers this?

[jeffnhiscars]

There is no connection between your dead trans and idle..other than that putting it in a working gear will add a load that will slow your idle. First thing to do it check for intake leaks and a smoke test is the most effective way to do that.