Surging/bucking

My '01 Lanos has 174k mi on it and recently showed Code P1404. I cleaned the EGR valve and throttle body with TB cleaner and replaced spark plugs and cables. The battery was disconnected while this was being done and the code was gone when it was reconnected. Idle was a little rough when the engine was first started, then smoothed out and ran smoothly during my test drive. After aprox 12 mi of driving, the CEL came back on with a P0137 code, which I cleared.

That was last week. Yesterday, the CEL came back on with five codes: 1) P0172, 2) P0137, 3) P0405, 4) P0172, 5) P0405. Since some of the codes indicate lean and others are saying rich, I'm guessing not all of these sensors are bad.

What the car is doing is surging/bucking at small throttle openings; 40-45 mph in 4th gear and 60-65 mph in 5th. If I take my foot completely off the gas peddle or push it to 1/2 or more, the engine smooths out and all stumble goes away. Running at 70mph or higher it stays smooth. Idle is also without any stumble.

Vacuum leaks? Bad EGR? O2 sensors?

Any thoughts appreciated.

Update:

The EGR valve was bad and sending confusing signals to the O2 sensors. Replacing it cleared up all of the hesitation and stumbling.

My hope is that most people start to buy this car, several incidents of these collisions will be reported and documented, and MB is forced to investigate. Hopefully that is attributed to a part for which a memory issue and not a mere "correction." I keep my fingers crossed, but I feel a little better knowing someone else out there is the same problem.


Not sure I understand your response. What problem are/were you having with your car?