Car is a 2000 Accord EX with 170k miles on the VTEC 4 cylinder that has a pesky misfire CEL for cylinder 3. Bad enough that extended idle time will make it flash and only cylinder 3, but the car runs reasonably well and gets 29mpg in mixed driving.. One owner car with lots of service records, regular maintenance.

Wires, cap and rotor are Denso and less than a year old,
Coil and NGK plugs are new.
Distributor shaft checked for play.
Valves recently adjusted and compression checked.
Timing belt done 15k ago.
Currently at a local shop and they can't find the cause, I suggested injector, seals, and harness and they said they checked those.
Checking around, cylinder 3 seems to be common but I haven't seen exactly why. Usually something on the list above sorts it out but no luck so far.

Any ideas what else it could be?

Thanks

 

Partially clogged EGR port would cause a lean misfire but not enough to cause P0401(insufficient EGR flow) to be triggered.

 

Thanks, sounds like something to attack next!

 

Bah, EGR would NOT affect idle though.
Verify that the spark plug boots are sealing properly. Prestolite and Sumitomo are the OEM plug wires. NGK is acceptable fit and finish, other brands may or may not fit correctly. Cheaper wire sets are known to have the boot pop off or not fully seat and cause a misfire condition.
Verify there is no oil in the spark plug tubes.
Swap the plugs around, if the misfire follows the plug then it is most likely the plug that is at fault. Verify the plug gap on #3 is not excessive or shows wear/damage.
I've had new plug wires be bad out of the box, beg/borrow/steal another set.

 

You can try swapping the fuel injector with another. See if the misfire follows it.

 

It ended up being a leak at the intake. The shop smoke tested it after swaps of other bits didn't fix it. .
They replaced the downpipe and intermediate pipe as well due to corrosion and now i have a p0420 for bank 1. Good times!