I wouldn't be on here if I wasn't in trouble m, I've tried everything I possibly can look up everything on the Internet read many many many many many forms . OK so here's my problem I have a 1998 Honda Accord EX They had the original F23a1 engine in it. That motor had an oil leak which caused the timing belt to go which made a huge mess . So I decided to get a Japanese F23a engine to put in the car . I bought the engine installed a new timing belt on it water pump spark plugs clutch pressure plate New intake manifold and throttle body gasket cleaned the entire intake and throttle body fresh coolant fresh oil transmission has fresh oil . So I put this engine got everything hooked up lowered the car tops all the fluids was super excited started right up fire great.started revving real high about 2100 RPMs and after about one minute of idling that high it start surging between 1100 RPMs and 2200 rpm's The idle air control valve is brand-new all sensors are checking out according to the shop computer I took it to which is a good friend of mine and no check engine lights are on and the engine is surging any suggestions please help me I am desperate any help would be very grateful

 

I'd start by looking for a vac leak......a hose the isn't connected, bad gasket seal, ect.

 

Try Scotty Kilmer's YouTube video "How to fix a car that idles poorly". It maybe your throttle is sticky and needs to be cleaned. It may be the Idle Air Control valve needs to be cleaned. It may also be that you have a loose hose causing a vacuum leak as previously mentioned.