My 91 850 has developed an issue on cold starts. Normally, the car would fire up and would instantly settles to a fast idle of about 800-900 rpms. Now upon cold starts, the car fires up instantly as normal (rpms wise) then it would go down to below 500 rpms and fluctuate there for a second or 2 then would settle to the normal fast idle. Seems like on several occasions the engine was going to die out, but somehow it has never done so. Car otherwise runs as normal and has full power. No problem on hot starts whatsoever. Not the classic intake gasket issue either the CEL coming on. Fixed this particular intake issue a few years back. Any suggestions? Thanks!