Stumped! INTERMITTEN rough idle

[fitguy]

I've have a 98 Stang-3.8 throwing a PO302 (misfire cylinder 2). For over a year, it's had a random rough idle. ACtually, it's really a violent shake. However, driving down the road or getting on it, there is NO power loss at all or skip. At times, I can feel a little hiccuping if I hold the rpms about 2,500 rpms... Not too bad, though. Again, this happens randomly. Other times, the car idles smooth.
WHat I've done:
changed spark plugs/wires
cleaned AIC
Cleaned MAF
Checked EGR
Checked Canister purge valve
checked for vacuum leakes
changed fuel filter
ran sea foam through the tank, twice

I have read where this could be several other things. I think it could possibly be a bad injector. what do you think?
Any wise suggestions is GREATLY appreciated.

 

[wmburns]

First do a through review of the charging system. Have the battery tested. Have the alternator tested for correct output and excessive AC ripple. Most autoparts stores will do it for free. Don't cut corners on the battery cables. Make sure they are clean and tight.\

Next inspect the spark plug routing. Make SURE that all factory standoffs and looms have been used. Are the wires touching any metal parts?

Clean the MAF. Use only a product designed for the job.

Change the fuel filter.

Change the PCV value.

Check for vacuum leaks. Even a tiny one will cause problems.

Are there any exhaust leaks? If there are any, fix them.

From this point on, things get more complicated and expensive.

Consider an injector cleaning and flow test service such as injectorrx.com. If this is a DD, sending all 6 out at the same time is a problem. Consider buying one new injector and rotate through until all are done.

IMO, it's a common occurance for ppl to replace spark plug wires on the V6 and do a piss poor job of routing. Poorly routed wires still misfire and most ppl stop looking at an ignition problem once the wires have been changed. Do yourself a favor and make sure the ignition system is in tip top shape before moving on.

Don't cut corners on the charging system. You maybe thinking a bad alternator couldn't possiblely have an impact on your problem. Your wrong. It could. The test is free. Rule it out before throwing away money on other things.

 

[fitguy]

I have done all of this except checking the altinator, fuel injection, and coil. I have pulled the wire off the coil and made sure it had fire. It's so random though. I will have the altinator checked today. how many volts should be coming out of it?

 

[wmburns]

Don't make something easy hard. Just rely on the alternator testing equipment. At home, you could test for correct output (generally anything above 13 volts is OK), but it's difficult for the home mechanic to correctly test for AC ripple.