I have a 90 GMC 350. Lately it sometimes has a starting problem when cold. If I start it without any throttle, it usually starts fine, but once in a while it runs terrible and pumps out huge clouds of water vapor. Warming the engine seems to make no difference. Idle is still so bad it almost dies. Wait a few minutes and try it again and it starts and runs fine. Seems like if I start it with a little throttle, it does it less often. Any suggestions? No codes or CEL. Almost seems like a very rich mixture. But temp gauge works fine. If it was a sensor, you'd think it would do it all the time. Weird......