Hi, can anyone help me diagnose a problem and figure out a solution

I've got a 99 bravo 1.2 TROFEO with 60000 miles on the clock. Sometimes when ENGINES starts but stops immediately if i dont push the throtle, or sometimes have problems at low rpm 800 when the car is stoped the engine is going alone under the 800 or stops immediately.

i have change sparks and air filter
maybe is the idle speed valve? i dont know were is this valve