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Hello, I own a 2002 impala, 3.8L.
Approx 140,000 miles

I commute to work and drive about 50 miles one way. When I get to work and shift from drive to reverse (I always back in to my parking spot) the RPM's drop, sounds like its going to die for a second or so. I give it some gas and its fine. From what I've read its hard to diagnosis as it could be a dozen different things. Mostly I've heard the MAF and Idle Control Sensor could be the cheaper/easier things to replace...

Any help would be greatly appreciated, thanks!
 

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Hello, I own a 2002 impala, 3.8L.
Approx 140,000 miles

I commute to work and drive about 50 miles one way. When I get to work and shift from drive to reverse (I always back in to my parking spot) the RPM's drop, sounds like its going to die for a second or so. I give it some gas and its fine. From what I've read its hard to diagnosis as it could be a dozen different things. Mostly I've heard the MAF and Idle Control Sensor could be the cheaper/easier things to replace...

Any help would be greatly appreciated, thanks!


Check engine light on? If so, scan for codes. That will point you in a direction, if the light is on.

Often, low idle and/or dropping idle (as if the engine may stall), is caused by the inside of the throttle body being dirty. The dirty bore and dirty edge of the butterfly valve prevents the proper bypass of air at idle, when the engine is warmed.

That is why when you stop, the engine feels as though it may stall. While driving, the butterfly valve is opened enough that there is no lack of air to the engine (unless the air filter is extremely clogged). If you stop and shift to park or neutral, you may not feel as though the engine will stall - although it may feel a little rough. Placing the car in gear puts a load on the engine, causing a drop in idle or rough idle. Running the a/c and/or turning the steering wheel while stopped, also puts a further load on the engine.

The 3.8 engine throttle body is easy to clean with spray throttle body cleaner, while still mounted to the engine.

The 3.8 engine also has a PCV valve assembly underneath the MAP sensor, which often becomes clogged and causes a rough idle. ACDelco sells a PCV “kit” that includes the valve, two o-rings and the black plastic holder (which usually cracks when the current one is removed). The kit may include the PCV valve SRPING - it not, reuse the existing spring. The kit is inexpensive - stay away from aftermarket.

Removal of the PCV valve kit assemblyrequires unplugging and removal of the MAP sensor, which is mounted on top of the plastic holder. It is very easy to damage the existing MAP sensor, if you are not careful. If you damage it, it can be purchased separately and also replaced.
 
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