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.