Replace valves for cylinder 1 for misfire at idle or low speed only

[Actormike]

Recently we had a water pump replaced on a 2004 Jeep 4.0L The next day it started misfiring on Cylinder 1. The engine never overheated and two shops agree there are no signs it overheated. The new shop is telling is the below and provided the video/photos.

Misfire is not present under load at all, only during coasting and idle conditions. Performed compression test on cyl 1 and 3. Both cylinders had close to 150 psi. Leak down test was very low. Connected a vacuum gauge to the intake manifold and monitored the vacuum. Noticed the vacuum is somewhat low at operating temp, and has consistent drops that coincide with the misfire. Suspect a valve issue is causing this condition. Likely an exhaust valve.
RECOMMENDATION- Remove head, replace valves for cylinder 1, have head machined and pressure tested, reassemble and retest.

Also, the repair cost is 1800.00. Is that normal?

PS we had already tried all the normal fixes like fuel injector, coil pack, plugs etc.


VIDEO:

 

[Gilaguy23]

I imagine you'll gets several responses on this. I did not listen to the video but I'll ask is the miss there 100% of the ytime while idling? Its been my experiance if a valve is burnt you'll get a constant miss or lack of fire off the bad cylinder(s). It will not have similar compression due to compression leaking past the burnt valve. It wont take much loss to make a miss at idle speeds, but the miss can be hidden at high rpm and you wont notice it unless the cyl is dead or close to it. Not disputing the findings, but it sounds like a occasionally sticky valve possibly.

 

[pagrey]

The vacuum is steady as far as I can see. There is a procedure Jeep recommends to de-carbon the valves. You can just use water. There is also a whole procedure to spin the valve if it's stuck. Personally I wouldn't spend big money until I did a bit more research

 

[Actormike]

Turns out the machine shop determined the head was cracked. If you listen to the audio in this video below, it still does not sound right to me at idle and seems a little rough, although the misfire is gone after the repair.
I cleaned the Throttle Body and Air Intake Control Valve yesterday but that did not resolve. Next step is to replace the Iridium XP Spark Plug I put in during troubleshooting with some Champion Copper Spark Plugs. The Coil pack is brand new, so surely that is not the problem.

I was really hoping it was the AIC but it cleaned up nicely.