This is actually for my brother's car. He had his mechanic install a JDM engine possible an S5 into his S4 (88 TII). For some reason his mechanic did't hook up the boost gage. The iddle was originally rough and the engine will die. His mechanic up the idle to 1500 rpm wich seems kind or high. The car however runs great once he step on it probably boosting higher and at a lower rpm than before, hard to know since the gage is not hook up but he thinks there is definitely more power. This mechanic has swap rotary engines before so he trusted him but it don't seem like this one went in right. Right now the intake hose elbow before the intercooler keeps blowing out when in boost.
Thanks in advance for your help

 

The boost gauge is driven off of the same signal the ECU uses to determin boost. They get the signal from the Boost sensor.

You could have the sensor disconneted (or more likely from your description he didn't hook the sensor up to a vacuum source and you have a major vacuum leak), but you can't disconnect the gauge without disconnecting all the gauges or the ECU.

 

Thanks Icemark. So a vacuum leak will create an overboost condition along with a crappy iddle?