91 960 Low idle

[gmtgmt]

my 1990 3.0 960 has a kinda low idle aproxmently 600rpm
its a little low and the engine rocks a slight bit but its not running rough or missing at all.

all vacum lines have been replaced in the engine bay.

Headgasket at 540.000km now at 570.000km new Intake gasket.
i have tryed spraying ether at the intake and no luck.

New spark plugs OEM volvo.
Tryed with a diffent working IAC valve
Tryed a used but working Throttle body from a engine with good idle.

only thing some time it kinda stumble wont take the throttle when i accelerate from idle but when it dose that i just floor it and it works again. it might happen 2 times a mounth maby less

also I have a Fuel smell from the rear when im at a traffic stop and some times when i park after a long drive, but no leaks and has good fuel econemy, its dry at the Fuel sender. The Fuel rail is not leaking ether

other than that it Runs like a raped ape to be excact. one of the best 960 i have driven and i have had 5 others.