No idle issues. No events or diagnostic codes.

But it seems that vacuum is a little low. Located about 650 ft.

It's a 2001 Cherokee, so distributerless ignition. The vacuum is just low enough that I'm wondering if I've got a timing issue of some sort. I've replaced all vacuum boots, and have checked for leaks (with propane). I cannot find any. Jeep seems a little bit sluggish.

I've currently got 74,500 miles on it, so it's still pretty low mileage. I figure that the timing chain is still in good shape and not causing any issues, but not sure I guess. I was checking with my scanner, and at idle, it seemed that 10 degrees advance was standard. I'm not sure what spec is suppose to be at idle.

Looking for some thoughts from some of you more experienced folks!

Thanks

 

10-14 deg seems to be where they run at idle.

I don't see a real issue with 16.5" as long as it's stable. 17-21 seems to be normal. You're checking with the engine warm, in P or N? No minor exhaust restrictions?

 

Jeep 4.0's do not have user adjustable ignition timing like other engines where you can rotate the distributor to set timing. Even in the 1999 or earlier models before coil packs. I would not worry about the vacuum numbers. Mine show a MAP reading of about 10.5 at idle but I'm at 6,500 feet which is about the same as 16.5 at your 650 feet. Timing chains are in spec as long as there is less than 1/2" deflection in them. Is your vehicle stock with stock tires? Lifts and bigger tires lead to sluggishness as well as many other things such as sticking breaks, etc.