Vacuum leak?
 

I noticed that suddenly my car, which normally draws about 18 lbs of vacuum, is idling at 13. Max boost, which is controlled by a manual controller, is delayed by 1500 rpm, or 5k. I can't find a leak in any vacuum line fitting. Would a leak in a charge pipe cause the vacuum drop? I thought I'd ask before removing undertray and searching. I've already sprayed starter fluid around with no results.

Low vacuum at idle with no increase in idle rpm points to a drop in VE. Has the timing belt been off since you noticed the drop in vacuum?

The only thing I've done lately is wire a new tps connector in. A wire broke on the original. Intake manifold was off a month ago and I had full vacuum after installing it. Car is idling well with no surging. Other than the lack of boost it's running good.

Megasquirt? If so what type and include your current tune and log.

It's a MS3 basic built by Reverent. About 3 years old. Log is 4th gear wot. I have another of slow drive, but I can't get it to load. I see I'm getting full boost a little sooner than gauge says. Makes me wonder if Bosch gauge is reading wrong, or maybe a vacuum leak somewhere under the dashboard. Please take a look and let me know what you think. I'll wait before I start looking any more. Thanks.

I took a good look at ic piping. Sure enough, where it comes up behind the headlight, it was contacting the body. I have a hole about 1/8''x3/4'' long. Patched it until I get a new pipe. Vacuum is still low. Vacuum stays steady at 34 kpa at idle. Compression cold is 175 on all 4 cylinders +- 5 psi. I'm thinking the plastic line that goes to the vacuum gauge has developed a slight crack, where the clutch pedal was hitting it. It still shows max boost, but low on idle. I'm going to pull the line off the gauge, plug one side of it and try to pressurize it to see if it leaks. If anyone has any other ideas I'm open to suggestions. I really don't want to pay someone to smoke test it.

Just seems like some sort of leak, the IC piping wouldn't affect it. Hope you find it

See Six’s build thread near present day and you’ll see info on how to leak test intake. Pulling the hose can work as well, but you still need to plug the turbo inlet.

Not saying this is related to your issue; it is related to smoke testing.

I went to silicone intakes site. They are out of the 3" intake tester. I got on a waiting list. They said that they should have them in stock around September 7.
I disconnected my vacuum/boost gauge, as that's where I was getting vacuum leaks. I took a wot log and compared it to my last one. Boost was slower and erratic. Virtual dyno has me 16 HP down as well. I'm pretty sure that I'm dealing with a boost leak issue now.
I have a taped patched hole in the pipe that goes behind the headlight. I have a new pipe on the way. I'm pretty sure that's leaking under boost. I've loaded a graph from VR to show boost from my last log and now.

Attachment 227706

If you can't wait, I made the same with a PVC pipe cap. This one was 2.75" OD like $1.50? Then ran a $7 or so transitioning silicone coupler for whatever size I needed. I think the valve stem was $2. Most expensive part would be the 1/2" drill bit and silicone RTV adhesive.

My failure was a worn silicone coupler being clamped with a worm drive clamp. Started leaking at 10psi exactly under the worm clamp drive mechanism.


https://cimg4.ibsrv.net/gimg/www.mia...f30fa1cb23.jpg
DIY intake leak tester with PVC pipe cap, silicone coupler (transitioning size if needed) and a drilled, siliconed tire valve stem

Edit for misspelling, due to cocktail in pic.