2006 Jeep liberty 3.6l rough idle.

Have one kicking our ass. 2006 Jeep Liberty 3.7l 115k miles. Came in with blown head gaskets and a cracked cylinder head on the pass side due to a leaking water pump. Symptoms were rough idle and misfire codes. The pass side head was replaced with a used one after sending both heads to a machine shop to be redone. After repairing the head gasket job the vehicle came back 3 weeks later with misfire codes and a rough idle. The misfire counter shows some misfires on bank 1 only during development and only feels rough at idle. Compression okay on all cylinders (over 200psi) leakdown test showed acceptable readings about 5-8%. Swapped injectors from Bank to bank with no change, new spark plugs, swapped coils, fuel trims okay on both banks, cleaned throttle body and IAC, performed crank relearn and last but not least replaced the timing system (timing issue was suspected and did find the tensioners clogged with debris). Still, engine runs rough at idle and although no codes have popped up, it's probably only a matter of time. Anyone have any suggestions or ideas on what we could check next?

After all that work I would want to verify cam timing and valve activity. I can't remember but is only the one bank Cams monitored?

Cranking Intake and Exhaust with a Pulse sensor and an ignition sync would be a quick check for any valvetrain anomalies.

Here is a known good:


If memory serves me correct that motor was prone to misfires on bank 1 after a cold startup due to aeration in the fuel rail, but that does clear up.

There is a TSB for lifter keepers.

Which misfire codes did you find, specifically?

If you use the 'Which Cylinder Is Misfiring' function in the scan tool, which cylinders are counting up? Are there any misfire counts stored in Mode $06?

I know you've done compression and leak down testing, but my first instinct is to suspect a leaking valve. I've had more than one 3.7L fool me in the past. If you did your first round of leak town testing with the tester set at 100 PSI, I'd do it again with the tester at 40 PSI. The lower pressure can actually expose a leak, whereas the higher pressure can inadvertently seal it.

How does the cranking cadence of the motor sound?

Intake plenum gasket Leaking? Vacuum leaks don’t show up really in fuel trim on map sensor engines. Does desired and actual idle agree? How’s engine vacuum look? Over 200 psi on compression sounds high like a partial stuck closed exhaust valve

If it's possible try to do an in cylinder running compression test. It's what helped me find a broken valve spring that was still holding on to dear life resulting in intermittent misfires on a Buick. Compression was good, leak down was good exhaust valve spring was broken.


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