I can't seem to figure out why my 2003 4.0 SOHC is missing at idle. It is not real bad. But you can feel it.
It has new OEM plugs. And new plug wires.
We swapped the coil pack.
PCV hose replaced.
I disconnected the IAC and idle dropped to 500 rpm.
I cleaned the MAF.
Injectors are new. The mechanic ran injector cleaner through it.
New fuel and air filters.
60 psi fuel pressure.
Can anybody think of anything else I need to check?
I bought this truck and found out it had a blown head gasket. It has 171,ooo miles on it. So I decided to rebuild the motor since it had to come out to repair it anyway. It runs good now. I just want to figure out this problem.
Thanks for any help!

 

The Ford 4.0l engines need Motorcraft or Autolite spark plugs, so good you got OEM, they pretty much EAT other Brands
And only Regular copper or Double platinum, single platinum with a coil pack is a waste of money.

OEM had 2 different spark plugs, both single platinum, but they were Bank specific, platinum tips on one bank, platinum electrodes on the other
This is because of Fords coil pack design

Try larger spark plug gap, spec is 0.054, go to 0.057
Or make sure all were at 0.054
At idle a Richer mix is run so engine doesn't overheat, too small a gap can misfire, but only at idle.

 

Thanks for the info. I'm not 100% positive of the plugs he put in. I think I will buy a new set and try that first.

 

As long as they were Motorcraft or Autolite they will last

The single platinum doesn't effect operation, just a heads up about wasting money, if you get 6 single platinum tips then 3 of them will wear out the same as regular copper on the bank with "reverse spark"