With the 240 in the garage for the winter I'm getting into the to-do list. The idle speed has been unsteady for sometime now, and it's been particularly bad - frequent stalling - until the engine is warmed up. I removed the original valve yesterday. It's a rather ugly job with the intake manifold and all ancillaries in place.

I intended to replace it with a nice shiny one I pulled from a relatively low miles PnP car a few years ago, likely a later 240 but may have been a non-turbo 740. With the original in my hand I see its Bosch part number ends in -501. The "new" unit ends in -520 with the rest of the part number identical. I'm hoping that the 520 is simply an updated unit. Anyone know if there is any significant difference between the two, such that the 520 won't work?

I'm aware there are methods to clean and free up a stick IAC valve, and that's still an option, but I'd like to try the later one first.
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Son's XC70, daughter's XC60, my 83 244DL, 89 745 (Chev LT-1 V8), and XC60. Also '77 MGB with Chev V6, and four old motorcycles. Long gone: 1981 244, 1994 940 and 1998 S90.