Rough Idle, What's Left?
 

08' 5.4l 3v with 101K miles. About 4 months ago I noticed a slight rough idle. I changed fuel filter, plugs, air filter, cleaned throttle body, MAF sensor, reset computer(helped for about 2 days) to no avail. No codes thrown. It's not horrible but it's rough enough to notice. Any other things to look for/test? Thanks.

What plugs are in it?

Moto SP509.

Should be ok. Did you use dielectric grease on the boots? It almost sounds like a small vacuum leak or a leaking injector.

Yeah, used grease. I thought about a vacuum leak. Any easy way to locate these? All hoses/connections look good.

Lean issue should be present with a vacuum leak bad enough to cause those running conditions. After everything youve done I would guess cops if they are original

Yeah, I am leaning towards that. No definitive way to test cops that have not outright failed though is there?

You can get ohm readings from the coils, but if it only acts up when its up to operating temp, you will need to test the coils when they are hot, which is quite difficult.

Yeah, I wish I knew someone with one of these.
http://www.tooldiscounter.com/ItemDi...le&kw=WAE76562

Wouldn't a dead coil throw a code?

If the coil was completed [electrically] open it would throw a circuit malfunction code, but won't throw a misfire code

Thanks. I hope it's just a failing coil. Other than buy the tool I guess only option is to wait until it dies completely or replace one/all of them.

Go on Ebay on buy a 10 pack of coils, that will give you 2 spare.

Are aftermarket coils ok?

Yep, they are good, and save lots of money.

Visteon/Motorcraft coils are the best for the money. The coils that are made in Hungary.

$180 a set I believe. Search "Visteon" via eBay and take advantage.

Get them while you can.