I have a 1994 B-150 Passenger Van -318 - I live in St. Louis with the 4 seasons and it is starting to cool off now. This problem has happened for several years now only on initial startup in the morning until the weather warms in the late spring, then it stops. I am retired so having to wait 5-10 mintues upon start up for the surge to stop is no big deal except for minor aggravation. The surge is not constant just back and forth. It stops as the engine warms - everything is fine - no idle problems, no acceleration problems. runs great on multiple startups after warming, temperature gauge reads OK. I've taken it to my local trusted mechanic, still scratching his head. Here are the things that have been tried to solve the problem. Upper and lower intake manifold gaskets replaced, replaced timing chain and gears, replaced thermostat and gasket, pcv valve, idle air control valve , check fuel pressure so on. Last thought is the computer - something is saying -" Wow! it's cold - hold on a few minutes -- OK! now I am warm enough, everything is OK - Let's Go!" Much THX for any ideas - Maybe the computer?

 

Could still be a vacuum leak somewhere...... Or, maybe the IAC bore is dirty. Could pull the throttle body, (battery disconnected please) clean everything really well, and see if that doesn't improve its attitude any.

 

Not sure about the 94, but later models had a 1-wire temperature sensor for the gauge and a 2-wire one for the engine computer to adjust the mixture when cold. If yours also has the 2-wire one I would try changing that since it could be sending wrong temperature data to the computer.