1998 Taurus w/ v6 Duratec, code po305

[ejb22]

The car has a pronounced miss at idle, and a code for misfire on #5 cylinder. I have checked spark and replaced the plug and wires. When the car is cranked cold and the idle is high - I do not notice the miss, as the idle drops, the miss is evident. The car has 72k miles and runs great otherwise. Thanks and I appreciate all help. Ed

[shorod]

A misfire can be caused by more than just a spark issue. If you have a fuel injector that is not working properly, low compression, or too much carbon on the valves/piston top, you may notice a misfire. A carbon build up would typically show up when cold rather than warm though.

I'd suggest starting by adding a bottle of fuel injector cleaner to the fuel tank and run it for 100 miles or so. I've seen fuel injector cleaner fix some pretty interesting driveability issues.

If you have access to a scan tool with a datastream mode, you can monitor the oxygen sensor voltages when the misfire occurs to determine if the air/fuel mixture is going rich or lean. This will help you determine if you need to focus on a spark issue or fuel issue.

-Rod