Help diagnose slight misfire in V8

[schadler]

I have a barely noticable misfire only when idling. It happens only intermittently...like every 10 seconds. It seems to do this only once warmed up. It's just a little "bump" in the otherwise smooth running engine. I noticed it a lot while towing my boat the other day...but only when I came to a stop. No problems accelerating or rolling at speed. I've recently replaced the plugs, wires, and I used some Chevron Tecron fuel injector cleaner (recommended by mechanic).

Here's what I suspect: I also have a bad (leaking) passenger side exhaust manifold gasket that makes some noise. Is it possible that at idle, some air is being drawn into the exhaust manifold and confusing the O2 sensor?

Anyone else have this problem on a 302?

 

[Ak LTD Xplorer]

have you checked your plug's.wires? how long has it been sense you replaced them..my dad's had a bad mif-fire..plug's fixed it good as new

 

[schadler]

I just replaced plugs and wires about 2 months ago.

 

[natedogco2007]

did you tie the wires up? i changed the wires on my mom's 5.0 and then the wire moved over and touched the manifold and burned through the wire. of course if caused a misfire. try checking the wires with the engine cool and off. if it is shorting out you could get a nice shock looking for it with the motor running.

 

[james t]

it also could be one of the coilpacks is on its way out. it usually starts out as a very light misfire only at idle and eventually works its way up to a hard misfire at all rpms.

 

[schadler]

Thanks James...any idea how I check that?