l drive an 94 lincoln towncar and it idles up and down from time to time and when l get ready to go into reverse or drive it quits and l have to crank it back up 3 or 4 time and l take off really quick so it wont go dead again l also get white smoke coming out from the back but not a whole lot....l do loose a lot of gas with this problem also. l was told it l it could be my oxygen gas sensor could this be it or what are the signs of it going bad?

Could be an IAC= Idle Air Control... also l have a 89 Town car that did the same thing. finally a friend took it to work & he did a fuel system service. Man it is like a new car now.. All of my prblems were solved...He said he had to run the system 10 times to get the crap out of it..
Mine was hard start, hard to keep running when cold,it would idle up & down, hesitation, if u stopped suddenly it would stall.so on & so on.The fuel system servicing was the trick, & it was cheap, I've heard of dealers charging hundreds of dollars for this inexpensive service.

not any real signs an o2 sensor is going bad, bad gas mileage and sometimes you will get the rotten egg smell can be called signs but the only way to know is with a scan tool so you can actually watch the o2 voltage, with the idle problem l would suggest a good tune up, plugs, plug wires, air filter, fuel filter and clean the throttle body, has the check engine lite come on? does the check engine lite work? if the check engine lite is on then start with that and go from there