Engine vacuum is erratic. Video attached

[MustangLX-5.0]

Am still in the middle of diagnosing the MAF / ECU issue. So I decided to check vacuum today. The results I got don't sit well with me. Well, here watch this video I have attached here. See for yourself. In the video, engine was idling. RPM's were not fluctuating and there wasn't any surging at that time. but the readings seem low. And the needle seems to flicker in tiny increments, and not to mention it also seems to slowly move up and down at times. I sure hope something isn't toast . Could this be heavily carboned up valves? I am NEVER hard on this engine. And heck, I have totally beat on my other car and the vac readings on that one are perfect. What could be causing this?

Oh and watch what the gauge does when I increase the engine speed.
There is a slight delay between the video and audio FYI.

YouTube - Mustang engine vacuum fluctuation

 

[jrichker]

Looks good to me. All the fluctuations were small amounts, less that 1" vacuum change. When you increased the RPMs , the vacuum went up to about 20", which is good.

Vacuum problems with valves are usually indicated by steady sweeps of more than 2"-3" of vacuum. Low vacuum would be less tha 16" at idle with a stock cam. Clogged exhaust can cause the vacuum to drop off when the engine is brought up to 1200 RPM and heald there for 30 seconds or so.

 

[90mustangGT]

It's not really bad, but not good either. Yes, that issue points to the valvetrain.

 

[MustangLX-5.0]

Could this just be caked up valves? I don't recall the vac readings doing this a couple years ago.

Ok, I know I should not compare the readings on my 3.8 versus the 5.0. Yes, 2 different engines. But the thing is, I immediately did a test on my 3.8 to compare right afterwards. The readings stayed at 20 at idle, then sharply dropped on hard throttle, then shot up to 24 at high RPM. After I let off the throttle the vac went to 25 then stayed there. Now, on my 5.0, the reading won't stay in the high after I let off the throttle. It falls back to 16 after settling down.

What is this? Burnt valve? Worn cam? I know the camshaft is a little noisy.. but it also is noisy on my 3.8. You can hear it pretty loudly in the vid. And look at how the needle shudders after I hold the rpms at 1700 (the first throttle increase).

Exhaust can't be blocked. pipes are gutted. I appreciate the response. But, you don't think this is that bad?