Yep. RM is one to check always. Your problem seems to be input related, that's why I suspect the low power connections to the GM- or the GM itself, esp if you've had trouble w it in the past. You need to hunt for water under there- its hard. Feeling down around the lowest section isn't possible, you have to undo the 10mm plastic retaining nuts with a 10mm extension/ratchet and lift the whole plastic frame (carefully so as not to crack it anywhere). You should inspect the underneath of the plugs that locate in the bottom of the frame if you have any cause for concern. BTW: water in there can last for years... hope it goes well!
Maybe swapping out the GM for someone elses would help narrow it down.
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08/88 535i e34 M30+miller MAF, 'stiens, tints & teeth!
All fixed now.
Removed the GM and the RM and after inspection returned them and everything was okay.
Took them out again and cleaned the connection with contact cleaner and replaced.
Everything seems back to normal.
Thanks for all the suggestions - much appreciated.
ss2115.
BMW 525i Touring - 1993 (current drive car).
DS23 Citroen Safari - 1974 (restoration and modifications).
Golf MkIII - 1997 (fun car and daughters learn-to-drive car)