It could just be bad GPs. If only a couple go bad the car will still start sometimes but it will be rough when it does. I'd take a tester to the GPs to check them again.

Even at 60 degrees I find that my cars hate to start without some glowing. They wil start eventually but man what a mess of smoke and rough running for the first thirty seconds.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique