The car sat for awhile over the winter due to a bad alternator. When I finally dropped the new one in and fired it up, the idle was high (1.2K rpm). The car drove flawlessly so I didn't bother to adjust it. My only mod at the time was a downpipe and the car was pulling about 18" at 1.2K idle.

I thought that maybe the unusual idle was due to a cracked gasket between the UIM and the LIM. While I had the UIM off I decided to do some work. I removed the AC and PS and all supporting lines/hardware, replaced the belt, disable the EGR, made a custom intake and replaced the gasket.

After about a week of work I fired her up and she sounds great. Strangely, my idle is fixed and now sits steadily at 800 rpm. My only concern is that the Greddy boost gauge is only showing 14-15" of vacuum at idle. Is this attributed the the new intake or should I be concerned?

 

My guess is yes. Look at it like this, the air in the intank track is moving more freely now with less restriction through the intank, the vacum at he same rpm will be less. Think like this, if you were to put your hand completely over the air inlet the vacum would increase until the car stalled. Some times I need to start a lawn mower with extra gas, say it it sat all winter. when I remove the filter and place my hand over the hole in the carb a lot of gas is drawed in with one pull. A hand choke. This sucks gas up from the tank. If the air on your car has a less restriction at a given volume it should draw less vacum. Does that make sense? I remember as a kid my uncle had a vacum gauge, but I never understood why it went down when he gave the car gas? Well the butter flys on the carb open and that causes a drop in the vacum. The air is free to go into the engine. Of course you did some work on your car and could of caused another issue to so its always hard to tell. I hope this helps and I could be very wrong too. If i am I'll get flamed and maybe learn something in the process. Terry7

 

Well, after I slept on this my advise is totally wrong. You have a leak some where. For some reason I forgot the vacum reads from in side the intank after the butterflys in the plenumb and changing the intank/filters won't really effect your vacum. A good intank system allows more air to flow but doesn't effect whats going on past the butterflys. Sorry for the false hope.

 

Wouldn't a leak negatively affect boost performance?

 

Vacuum is dependent on engine speed. With the engine warm, give it just enough gas to hold 1200 RPMs and see if you still pull 18"

 

Agreed ^^^. Vacuum reading will vary with engine speed. Try this some time: get the engine up to 4k rpm while coasting down a steep hill and let completely off the throttle. This throttle position will be the same as when the car is idling, but you should get nearly 30 inches of Hg vacuum. Put the clutch in and put it in neutral. Watch the vacuum drop as the rpms do, all while the throttle is closed.

 

If i get 9-10 in Hg when my BP is idling i am happy, this is at 1500rpms

 

I guess it took a while for the stock ECU to catch up. I'm still pulling 16" at 800 rpm.