I cleaned my EGR valve - some carbon buildup but not too bad - I checked the suction on it and it seems to work fine, I also changed out the o2 sensor but the problem remains - now however it doesn't want to idle at all warm or cold (so I couldn't do the dwell test) - runs okayat other speeds though. Seems to me to be either the mixture control solenoid or the computer. I can get a mcs for about $110 or I can get an exchange carb for $269 from national carbs. This is starting to be a real drag.

 

Won't idle cold either? Is the choke valve closing when you give the gas a good pump cold? Have also seen many with sticking choke valve and/or linkage that a good spray with carb cleaner and then lube with WD40. The cold idle and warm are fairly independent of one another is why was asking. Forgot to ask the obvious. Can you adjust up the warm idle speed and runs ok? Idle speed screw on rh side of carb and sticks way out there so hard to miss. Also the mixture is adjustable but is behind a split pin at the base of the carb. Can access by either removing carb and then split pin but I just use an old front brake pads spreader spring from Protege. The spring is 'L' shaped on the end so you can adjust mixture by only a 1/4 turn at a time but works great. Give that choke valve a good check and make sure the fast idle cam is turning with the valve.

 

Tried cleaning and then lubing the choke controls and still no help. ECU? mixture control solenoid? vaccum leak? there are so many little black hoses connected on or about this carburetor its unbelievable I can see why people swap them out for a webber. I think it's time to take it to a trained professional for further troubleshooting. Thanks for all the advice, I'll let you know what we ultimately come up with.

 

I recently got a 1988 B2200 in very nice condition, and the idle ran high probably above 1000 rpm, but it purred and started nicely. When I brought it in to have it checked out, I had them lower the idle. Now, it will not idle well when cold, does not start quite as well, so I am going to go raise that idle a bit.
Perhaps this will work for your '90?