Misfire still.......any suggestions?

[RangerMax]

Hey everyone. I'm working with a 2005 Ranger Edge 2WD 3.0. Lost the bottom end of the engine due to a cam synchro a while back. Finally got it running again this past weekend. Took my '05 top end (172,000 miles) and put it all on an '02 bottom end (202,000 miles). Used a new engine gasket set. I went through the rocker arm torque sequence twice just to make sure it was good as I was putting the engine together. Fired right up and drove fine for two days.

Started idling pretty low (5-700 RPM) and rough two days ago. Check engine light comes on, then starts to flash. Codes are P0304 (misfire cylinder #4) and P0316 (misfire under 1000 RPM). I have a code scanner, so I erased the codes after each of the following attempts to track down the source.

Swapped spark plug wires between #4 and #5 hoping the code would change to cylinder #5. Wires have less than 3000 miles on them. Code stayed at #4.
Swapped the coil pack. Code stayed at #4.
Installed new plugs and verified the gap at .044 on each plug. Code stayed at #4.
Found someone online with a similar issue and it turned out to be a PCV valve. Swapped PCV valve just to see if it would work. Code stayed at #4.
Swapped fuel injectors between #4 and #1. Code stayed at #4.
Sprayed carb cleaner strategically around the engine while it was running to check for vacuum leaks. No leaks.

I found that if I keep my foot on the gas pedal to keep the RPMs at 1000, the engine idles fine and the check engine light stays off. Take my foot off the gas pedal, idle drops to 5-700 RPM, idle is rough, the CEL comes on within 30 seconds, then it starts to flash.

As a temp fix, I bend the tab on the throttle body (where the idle speed adjustment screw would be on a standard carburetor) so the engine will idle higher. Idles between 900-1100 now. CEL does not come on now, but I also know that this isn't a true fix.

I know about the exhaust valve seat issues on the 3.0 engines for '04, '05, '06. Next step is a compression test and leak down test to see if this is my issue. I doubt it since the heads have 172,000 trouble-free miles on them, but I guess it's a possibility.

Not sure what else to check or do. Any suggestions?

 

[91stranger]

You said the cam synchro went bad before the rebuild but you didn't mention if you replaced it or if you put it in correctly. If this cam synchro is put in wrong it will pull misfire codes. I think it's normally a 1309 code but if it could throw other codes as well. Did you check you cam synchro since doing the rebuild?

 

[rusty ol ranger]

Hows your idle air control look?