I was checking vacuum at power boost. Then noticed motor runs with line unplugged. But when you put gauge to line or just cover with thumb, motor stalls. What could cause this?
Would like to know what caused you to want to check vacuum at the booster to begin with.
Typically the engine RPM’s will go up when you induce a vacuum leak such as removing the vacuum brake booster hose. This is NORMAL.
While the hose is disconnected, the IAC – Idle Air Control will try to compensate and upon plugging the hose may sometimes cause the engine to stall. Simply restart the engine and it should compensate.
If you were having idle issues to begin with, the IAC may be sticking.