My 90 also does this, but it's also pretty far from stock. How long does it take for this to go away?
I know on mine, I can just rev it a couple times after it running for 10 seconds or so and it's good to go. If it doesn't take long, you may not have anything to worry about. You really should let your car warm up a second in cold weather before just taking off anyway (although I'm not really sure why... I've just always heard it, could just be an old wives tale).
You may want to try cleaning your MAF by spraying it with some electronics cleaner. This is especially true if you are using a K&N type air filter that has to be oiled. The oil is bad about getting on the sensor.