97 Taurus: Smoke around engin

I have a 97 Taurus Lx with about 150k miles on it. I think I have warped/blown head gasket but I am not sure (since I had a vacume leak 3000 miles ago!), so I really appreciate your ideas. Here are the observations.

Bad news:

– Engine lopes in idle (and it gets dangerous when you drive and want to stop for the lights)

– After it warms up lots of whitish smoke is seen around the engine



Good news:

– Coolant level doesn’t change.

– I don’t see any color change in the oil.

The, “…it gets dangerous when you drive and want to stop…”, sounds colorful; but, it doesn’t tell us what gets dangerous. Can you un-obfuscate that for us?
White smoke can be fuel which has vaporized, as well as water (or, coolant). Did you smell the smoke?

About the smell, something between oil burning or rubber burning smell.

The danger of " … when you drive and want to stop…" comes when I hit the brake, the engine RPM gets so low that it shots off the engine and causes full stop. So when I want to slow down or briefly stop (for a “yield” sign), I put the gear into Neutral and try to make sure that in case engine rotation comes down I can push the accelerator to avoid engine shut off.