1997 Camry 2.2 surging

My husband and son just put an engine in my son'e 97 Camry 2.2. It ran great, but there was a leak in one of the injectors. They replaced the injector o rings, and now, when you crank it, it surges while it is running. It goes from normal idle to a very fast idle and back down to normal about every 3-5 seconds. Any one have any ideas on what could be causing this? Thanks for your help.

Check your EGR valve for heavy carbon deposits (clean if heavy deposits are found) and EGR valve diaphragm for proper/smooth function. Check the EGR vacuum modulator and VSV for EGR for proper function.

Just replaced the Egr valve and now it idles but its at a steady 2200 rpm and will not drop but you can give it gas and it will take the gas like it should. any other ideas?

See if the engine coolant temperature sensor is in spec, and has good connection to the harness, and the harness is good.