I have a 95 maxima, and when the car is in park it idles around 750 but it dips down to 600 every 10 seconds or so...when it does it, it sounds like the car is about to die off but it picks back up. also, sometimes when it drops it squeals like when you need power steering fluid or something is wrong with the belt. Is this normal?

 

No.

 

I had the same thing, but without the squealing. I replaced the plugs with NGKs (they weren't before) and it went away.

 

Lies, perfectly normal

(check your IAC valve, might need cleaning/replacement)

 

Agreed on the IAC.

May also be a TPS.

Does it do all the time or within some timeframe after startup. If so, the coolant temp sensor may involved.