Chrysler Repair: 98 Chrysler neon, chrysler neon, neon 2

Question
Hello,
I have a Neon 2.0 litre (export in Australia) and it surges when you take your foot off the throttle on a slight downward slope. Under low revs at around 40 miles an hour it does the same thing. All the codes come up ok at the dealer. Any ideas would be great.
regards
Allan.

Answer
Hi Allan,
This sort of behavior is most often due to air leaking into the intake manifold which dilutes the mixture which is then sensed by the 02 sensor which adds fuel to bring the mixture back to normal. The result is just like opening the throttle a bit, thus you get a surge in rpm. The fix is to trace all the vacuum lines that are attached to the intake manifold to their temination points looking for loose fittings or crack in the lines. Use the underhood sticker which shows the lines as a road map. If you have a spray can of carb cleaner you can very carefully spray a very short burst of fluid at each joint while the engine is idling. When the fluid is sucked into the leak the engine rpm will change momentarily which is the tell tale sign the you have found a leak. But use very little and don't spray on the exhaust manifold so as to avoid a fire. An alternative is to spray water from a spray bottle in which case the idle will drop momentarily. You might also check the fasteners on the intake manifold which if loose could allow a leak around the gasket. Torque from the middle to the ends in a back and forth sequence, torque value is 105 inch-pounds (~ 9 foot-pounds).
Other possibilities, though less likely, are problems with the fuel supply/injectors, egr system, bad 02 sensor, or torque converter lock-up solenoid, but those would likely set a code in the engine controller.
Roland