15" hg on the MityVac at the PCV hose It was vibrating a lot back and forth but not as far as the next line wither way. The Mity Vac manual says it should be steady.
Edit- When I revved it the needle would drop below 10 then jump up to over 20? Oh yea stuck the vacuum up the tail pipe no bubbles around the exhaust manifold or the Y connectors where I could see them. Used dish soap and water in spray bottle.

 

Vacuum at idle is low. You have a leak somewhere. Other behavior is normal.

 

Sprayed around the manifold, injectors the evap purge valve and EGR with propane and starter fluid no reactions from the motor. Also took off air cleaner to spray the new MAP no reaction.
Looks like a couple of the lines from the evap canister go along the firewall and down behind the motor. Any idea what they do? They are not on the vac diagram I have. This one https://www.justanswer.com/dodge/1ji...-9-engine.html

 

15 is a bit low. I like to see 17-20 at idle. Part of that may be the type of gauge you used. I have a dedicated gauge just for engines. I would next test a vacuum line to the distributor or throttle body. You might need to add a tee to do this. The flutter is troublesome. It may be late timing from a worn timing chain for the low vacuum . The flutter though, can be a bunch of things. A sticky or burnt valve can do this.

How many miles on the engine?

 

I do not recall one going to the distributor. Saw the one I was asking about connects to a hard line behind the dist along the firewall. Still not sure what it is and as I write it hits me its the gas tank. I can probably pull the one off next to the MAP. I'll have to find some hose, I think one of the T's in the kit will work. this is the mity vac I used https://www.harborfreight.com/mityva...ump-39522.html

 

I have a similar tool to bleed brakes and actuate solenoids on older vacuum controlled ventilation systems. I use this vacuum gauge as the large dial will let you see little flutters when tuning an engine for the track. You may not have a line to the distributor. This was built about the time they were going away.




Now, this is very important. How many miles on the engine. More, or less, than 120,000 miles? Issues with a low mile engine may look the same as a high mile engine but the causes can be different. Have you checked for timing chain stretch?

 

Sorry I went to look and forgot to mention 160K TC and tensioner new 5 years ago double roller. Heads look to be replacements when I had it apart for the plenum. It had an exhaust leak due to broken manifold studs that I fixed. All new exhaust Y back. Rebuilt trans and the addition of an aftermarket Crank Sensor made a huge difference in how it ran after that.

 

I'm going to stop for the day. Be back at it tomorrow.

 

Recheck your plenum.

The lines for the evap go back to the charcoal cannister. They are notorious for drying out, and cracking.

 

Felt better so I put the vac on the T coming off the ball on the firewall. Got a solid steady 17.5 or 18"hg I think it had a tighter connection than what it had on the PCV hose off the intake.
I did not check the plenum. I'll take the TB off and look in tomorrow.