check engine light.....thinks the mechanic screwed up

[malibusmostwanted]

i just had intake gasket redone and all the cooling stuff..well they said the check engine light was on...it wasnt when we drove it there....they ran test to get it to shut off but it came back as egr valve i think is what its called...i had them replace that...everything was fine until next day when as soon as i turned heater on the check engin light came back on..there is a noise that sounds like a baseball card in bike spokes when heater is on now and shut off when heater is shut off...we went through over 8th tank of gas in one day like 5 ucks worth...dont sound like much but we normally could go 5 days on 8th tank of gas goin to exact same place, wich is only work then home.

anyone know what could cause these problems....diagnostic came back as that valve problem only

[peterdash69]

well i have a 2002 mali and my engine light came on and it was the o2 sensor