I have a 1997 Del Sol it had a 1.6 non v tec type s. I installed a d15b vtec jdm. I did not change the ecm but I was told it would work fine but the v tec would not work. Motor ran great for about two months and one day out of the blue it just started reving up and down at idle from about 1000 to 2500 rpm's over and over again. I can un- plug the iac and map sensor and it will idle smooth but extremly rich I plug the sensors back in and it runs smooth until I shut off the engine and re-start then it starts the constant reving up and down again. I have checked for vacum leaks and there are none. I have changed the throttle body same problem. I have changed the intake gasket same problem. I'm thinking iac or ecm.