I have a 99 Nissan Sentra 5 speed manual. I just changed the thermostat and now the car idles just a bit lower and wants to shut off when coming to a stop. Does anyone know how to fix this? 

does it have an idle control near the steering wheel? i dont think there is a connection between the thermostat although it adds poer consumption to the engine.

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 No idle control. I was told that it can be a loose/broken vacuum hose, but shouldn't I get an engine light for that? Besides, I was nowhere near any vacuum hoses when I changed the thermostat.

 Friggin automobiles.......you fix one thing and something else goes.

first off,was it the exact thermostat that nissan said to replace with? did you replace any fluid that leaked out? and did you run the heater to temp to purge any air in the system after you installed it? last step very important,i just replaced my thermostat 20 mins ago.and car is running fine following all the above steps.good luck.

 Have your tuned up and retime it it might be retarded if after the job and still the idle is not stable try to clean the carb or the throttle body.