Toyota Repair: 90 4 runner, combustion test, head gaskets

Question
my  4runner is hard to start when it is cold out, it cranks 10-15 times before starting. i have replaced the cold start injector, 02 sensor, and plugs. the plugs were fouled from it running rich because of the bad 02 sensor, i haven't noticed any loss of coolant or excessive oil use, but sometimes when i start it, it puffs out some white smoke, thinking maybe head gasket? what do you think?

Answer
These engines had chronic headgasket problems and there was an actual special service campaign(SSC)if applicable the head gaskets were replaced at no charge with no mileage or time limit, it may be worth the time to have the toyota dealer check to see if this SSC still applies, they can run the VIN# and see if this may be the case, if not there is a simple internal combustion test that can be done to check for leaking headgaskets.