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S500 | 220.175 | 113.960
363 Posts
Discussion Starter #1
I've had CEL come on every once in a while due to O2 sensor going bad and old rattling CAT, so when it came on today I didn't pay much attention.

About 2 miles down the road I noticed my engine shakes slightly on idle at 500 RPM. When I start accelerating the shake would get more noticeable and go away at around 2000 RPM.

My immediate suspicion an engine misfire, perhaps due to clogged fuel filter, BC it was never replaced and I am at 160K ODO on my '01 S500.

I went to auto zone right away and they pulled codes:

P0300 random cyl misfire
P0130 O2 sensor
P0305 cyl 5 misfire
P0150 O2 sensor circuit
P0600 loss of serial communication link

As the gentleman was pulling the codes, I had to start the engine and since that time the car did not show any signs of misfire anymore.

Afterwards, I drove it another 5 miles, few engine starts and once again, no sign of engine shake/no evidence of misfire.

I don't know if this will come back, but I need some help dear fellow forum members...

Does this sound like a fuel filter gone bad? Should I check that first or the wires and spark plugs under the hood?

New fuel filter at auto zone is 40 bucks.
Thank you very much gentlemen.
Any input would be a blessing!

Best Regards,

'01-E320 & 02-ST2
31,631 Posts
What happened was that a misfire was serious enough that the ECU shut down the cylinder, that's when it was really noticeable. A stop/start cycle reset the ECU so it was firing again.

Not changing O2 sensors isn't the best way to proceed. The resulting fuel mixtures can melt cats, which are expensive, as well as wasting fuel and causing misfires. You are in a part of the country where you can fit inexpensive aftermarket cats, and the O2 sensors are easy enough to change yourself. Why not fix it properly?

If you haven't changed the fuel filter, then I'd do that anyway, but take care of the obvious ones. And I'd get a genuine Bosch filter from a reliable source, like or rather than whatever autozone might have. Buy an air filter with it at autohausaz and you'll hit the $50 mark and get free shipping as well.

Once you have replaced the cats and O2 sensors (the fronts are really, really important), then you can see if the misfire issues return. If so, and you have already changed the spark plugs (due at 100K miles) then swap the coil (but not the ignition wires) on the #5 cylinder with the number 1 (these would be the first coil on each bank). Be sure to connect the ignition wires properly, there is an a and b wire for each cylinder. If the misfire moves, then you know it's the coil. If it does not, then swap the ignition wires (both of them, again, a to A and b to B) and see if it moves. If it stays on #5, then you either have a bad plug, a leaky or clogged injector, or a far more serious problem which would be very rare and expensive.

But it's probably something simple.

Good luck.
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