Ok , egr (exaust gas return/ recirculator) recurculates exaust gases"hot" back into the motor for emissions and better gas mi , this doesent even open till you are driving the car at when it is all warmed up and there is a pretty high vac count"cruzing at one speed 15inch pounds of vac or more" but over time this system builds up alot of carbons and doesent to anything but waist power. it would not and i repeat would not cause the top of a piston to crack , If you want i have a engine scanner a OTC 4000{ENHANCED} I will scan the engine for you and let you know what is going on and even fix the problem for you if you want. send me a pm and dont worry I have my ase's and alot of ppl will vouch for my work , But if you continue to listen to shops that are going to lie to you all you will be in is more shit.