Engine noise

The oil and check engine light came on. Had the oil changed took care of that light, so my fiancé put his code reader on it and came back with a misfire code. So my fiancé changed three front spark plugs. When we went to turn the vehicle back on it does this constant repetitive vroom noise and when you push down on the gas it almost makes it shut off or idles low. Never had that noise or problem before the light came on. Not sure if he did not do something right or why it is messing up. He tried putting it in gear as well and the noise gets worse.