Question93 Eldorado 4.6 Northstar(160k miles) surges at an idle in gear. Replaced TPS, IAC, Computer, Crank sensor,Fuel pump and sending unit, fuel filter, EGR valve, map sensor, spark plugs, wires and transmission. The surging is so much the vehicle feels like it is going to stall. It will run good after the idle, so I do not think it is the timing chain.
Answersurging can be caused by vacuum leaks around the intake manifold or leaks in the exhaust manifold gaskets or any other exhaust leak ahead of the oxygen sensors.
It can also be caused by a blackish residue within the throttle body and on both sides of the throttle plate area that needs to be cleaned off using an aerosol spray type cleaning agent.
A mis-adjusted TPS can also cause surging.
