Here are some causes of surging.
Fuel Pressure: Test for proper fuel pressure with a fuel pressure gauge. Connect the gauge to the test port on the fuel rail. Fuel pressure reading's very depending on the system your in our vehicle, but most throttle body injection cars (TBI) are between 13 psi and 17 psi. And most (DPI) direct port inject systems are between 40 psi and 55 psi. To find out your vehicle system fuel pressure consult a repair manual. If little fuel pressure is present the fuel pump needs to be replaced.
Plugged Fuel Filter: A plugged fuel filter can cause an engine to surge. The fuel system supplies power to the engine through combustion, if fuel can not be delivered it will cause inconsistencies in performance. To check for this condition remove fuel filter and inspect, replace with new unit and recheck.
Vacuum Leaks: If an engine vacuum leak is present it will cause the sensor input readings to the ECM to be incorrect causing an engine surge. The system is programmed to work at prescribed value. When a vacuum leak is present these readings are incorrect causing the engine to surge under power and idle rough. Inspect the air intake boot for tears and vacuum feed lines to all accessories. Replace torn or dilapidated hose with a new hose and recheck system. Also an IAC (Idle Air Control) valve bypass hose it can develop tears/holes mid way through the hose, inspect thoroughly (common problem on Ford trucks and SUV's) Sometimes a vacuum leak can be detected by opening the hood, start the engine and allow to idle, then listen for an audible whistling sound. Then inspect that area of the engine compartment to locate leak.
Plugged Exhaust System: The exhaust system in your vehicle is designed to release exhaust gases from the engine to the rear of the car. This system is designed to have about 3 pounds of exhaust backpressure under full throttle. This means the engine should not have to push more than 3 pounds of pressure to release the exhaust at any given time. If a catalytic converter plugs or breaks apart it will plug the exhaust system causing an engine surge.
Weak Ignition Spark or Failing System. A weak ignition system can be a sign of a failing ignition component and cause the engine to surge. Remove spark plug wire and insert an extra spark plug into end of wire, attach spark plug to engine ground then crank engine. You should observe blue spark between spark plug gap. If a yellow spark is observed, your ignition coil is weak and needs to be replaced. Also the spark should flash in a constant rhythm, if the spark is inconsistence suspect the crank angle senor, ignition coil or ignition module.
Saturday, October 18th, 2008 AT 11:07 PM