4.6L Rough Idle/No load hesitation
 

Hey Guys, Got a problem and am looking for ideas hear.

I have a 2005 4.6L STX with 150K on it.

The Idle is rough and low. At around 1200 RPM cruising you can feel the engine sputtering and it is a tad slow off the line due to the low RPM fluctuations but while going and under load there seems to be no problems.

Recently have....Cleaned the TB, Replaced plugs and COPs, replaced air and Fuel filter. Oil is changed every 5k and have no signs of leaking fluids...meaning Coolant is not low, no smell of coolant in the exhaust, no coolant mixed with oil, not running hot etc. Oil levels are maintaining and not lower than a half of a quart between changes

Any Ideas on something I might have missed? Appreciate all the help.

I had to replace two of my coil plugs. The wire harness in the truck. When I removed them from the coils while the truck was running there was no change in the running of the truck. If I jiggled them the idle would change. Only on two coils. My truck is not the same as yours but maybe that is a help?

I would change the TPS

Ck for missfire codes . Ck Mode 6 info for non flagged missfires . If It is missing , It should show. Unless the counters have been turned off , Haven't seen that in a while though .If you can't do that , go old school and unplug one coil or injector at a time . One that does not change anything shows a cyl. to look at closer .

Guess I should have mentioned I have gotten no codes like I was getting before the COP/Plug change

Mode 6 will show counts before ECM flags a missfire . Try the unplug of each one at a time if you do not have a scanner with mode 6 ( non continuous monitors ) capability . Missfire pid on Ford vary by year and scan tool. It will show 1-10 with counts on most scan tools . 1 being cyl 1 ect. You can have a missfife that has not turned on the ck eng. light yet . It has to pass a preset # before the CEL is turned on .

Thanks JWC for the explanation. I do not have a scanner, guess its about time to invest in one though...always useful.