My 1998 E320 is losing power and throwing the codes po300 random misfire) po305 cylinder 5 misfire) po306 (cylinder 6 misfire). Since 305 and 306 affect the same side of the motor, I am thinking that this problem is most likely a cat or o2 sensor on the same side. The car will sometomes drive at various speeds for a long time before the car loses power and throws the codes and says check engine electronics.

My thoughts are that a cat would not come and go as a problem and would be accomanied by the usual loud sounds associated with a bad cat. Also, I have noticed that the problem usually occurs when the car is under a load and going up hill with higer RPMs. Although sometomes it happens when I haven't even gone around the block once. Other times it won't happen at all. It does seem like the problem is becomming more consistent as times goes by.

Any ideas. Later I am going to try to remove the 02 sensor on the same side and see if it runs better. The problem is being able to do so when the problem happens. I never seem to have the right timing.

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1998 E320 150,000
1980 300SD 240,000
1965 190D 79,000

The left side cat is a good possibility.

However, start by moving coils and or spark plug wires around.

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Thanks for the advice. I ended up concluding that it was the cat since removing the front 02 sensor prevented the car from throwing the error codes. I have removed the old cat and have the new one 90% back in. I will report back.

FYI Don't run car too much after removing the 02 sensor. The hot exhaust can melt things under the hood!

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1998 E320 150,000
1980 300SD 240,000
1965 190D 79,000