Well.........we finally got the '91 240 started....after much cranking, swearing, and checking connectors, new cap & rotor (just because).....just get the feeling of possible icing in the fuel lines...put in some dry gas just for fun........too damn cold to do much else.......now.....for the question....got the thing idling.then after a couple of minutes of normal idling....it goes into a 3-4 sec cycle of...normal idle,decreased idle and a puff (similar to a very slight backfire ) out of the tailpipe....repeat every 3 sec......ad infinitum.......or at least for 15 minutes....then drove off...smooth operation while driving.....anyone seen this cyclical behavior before???????.......any help would be appreciated..................j.

Sounds just like water in the fuel to me. My son's 244 sat unused in CT last year for 4 months in the fall when he was off at college, with at most a quarter tank of gas in it. Sumbitch cranked like crazy when he went home for Christmas, but could only get a little pop evey now and then. After struggling with it for a day or more, he added dry gas and several gallons of fresh gas and eventually got it running, with exactly the 'puffing' you described. Once it was fully warmed, on the road and had a full tank there were no more problems.

Could it be your Air Mass Meter? I was having cold starting problems when the temp dropped to freezing. Finally had no luck starting at all. Replaced with a used AMM I had from the U-Pull-It ($15) and it's going strong now.
Good Luck, Jeff