I suspect a dirty or malfunctioning Idle Air Control Valve. It's located on top of the throttle body and is easily removed by two bolts + a small wiring plug.
Try cleaning it with brake cleaner, blow dry with air. Re-Install. If no better, replace unit. While you're at the throttle body, remove it completely and clean out any oil-blow-by contamination on the throttle body internals. I use brake cleaner without any negative transient effects, regardless of the little sticker which may be on the unit saying "don't use any harsh chemicals to clean." Make sure the vacuum ports are all clear. Re-Install.
I do NOT suspect a faulty EGR valve because EGR's typically just stall the vehicle; they don't cause surge.
But to eliminate variables, temporarily remove and plug the EGR vacuum line to keep EGR dormant during testing. Note any change in performance. If the engine still surges, then the Idle Air Control Valve is searching for position and/or sticking at various stages.
In conclusion, I suspect your issue rests around the throttle body area. IAC Valve and/or dirty throttle body.
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Thursday, December 18th, 2008 AT 9:28 PM
