i have a 99 nissan maxima i want to know how many o2 sensors does the car have also wen im sitting at a red light my car starts to shake a lil bit like its hesitatin but only wen its at a red light or stop but if i put it in park or neutral its fine wat could cause that

 

There are 3 O2 sensors I think. And the shaking, I dunno lol

 

Could be an EGR issue, or just a dirty IAC valve. Cleaning is easy and adjustment is necessary afterwards, but requires you just turn the screw to get proper idle rpm (I think 700 RPM)

 

Adjustment is not necessary afterwards. Leave the idle screw alone.

FED spec has 3 O2 sensors, CA Spec has 4.

When is the last time you did a full tune up?

 

I think there are three also, go to www.courtesynissan.com and hook into beta site for parts explode on more than you will want to know probably, as far as the shaking,,,,,,,well your rpm's dip when at a light or stopped in drive or reverse, I assume your an automatic trans, there are a ton of things that can contribute to this, dirty air, fuel filter, usually affect your running at speed also, general tune up issues....emission related or even crappy gas.... there is much more also so, take your pick base on the limited info you've given here.

 

I read and follow the guidelines in the maintenance manual, which calls for adjustment IF idle is not in the nominal range. So, adjust it on your call.

 

The OP mentioned he has a rough idle, not that his idle is too low or too high. Adjustment may be necessary, but it's not always the case.

Rough idle can be attributed to many things, and can be independent of the idle screw.

OP needs to give a better/clearer description to get better/clearer advice IMO.