I have a 1989 Toyota 4x4 with a 22RE engine. I replaced the cylinder head after getting a couple of bent valves from the timing chain slipping. My Question is the engine runs smoothly upon start up , but then starts surging after its warmed up. When I disconnected the vacuum hose from the EGR valve or the BVSV valve it stops surging. My guess is the EGR valve is stuck partially open any Suggestions?