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P0306-extremely Rough Idle 01 4.3l



So yesterday on my way to work my ses light comes on, not much i can do at that point. Engine seemed fine and still running smoothly. On my way home still running great until i head up a steep upgrade and down shift to 3rd to pass up a few truckers struggling up. I notice the engine shaking badly thru my gear shifter and the ses light begins blinking. Instantly notice a loss of power. Stop by the parts store to run a dianogstic and get the code p0306. So i make it home and my engine is shaking pretty bad, idleing up and down to the point of almost dying and bad exhaust fumes. I change all plugs/wires and checked for any exhaust leaks. Engine still starts and even runs but the shaking/sounds are unbearable! I take good care of my truck, only has 81k on her. Any ideas?

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Could a bad cat cause this problem? And if so, how can a tell a bad cat besides removing it?


My GM factory fuel and emissions service manual has a couple of ways listed to check the exhaust for blockage.


One of these is to remove the forward oxygen sensor, then connect an exhaust backpressure gauge to the opening. Then the book gives test procedures from that point on and what the reading(s) on the gauge should be. (You would be best to look in the book for your year/model vehicle to get the test procedures and pressure reading for your specific vehicle.)


This is listed under "Restricted Exhaust System" in the index at the back of the fuel and emissions service manual.

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