After installing crankcase ventilation system my engine idle jumped to 1200 - 2000 rpms. It did not have this system when I bought it for some reason it had been removed and the vacuum port at the back of the motor had been blocked off. It ran fine this way. Now it throws a code of P1506. I replaced the IAC and the TPS and checked for vacuum leaks. Any ideas how to lower the idle and why would the motor run smooth with the vacuum completely blocked off? I also completely covered the ports under the IAC and there was no change to the engine idle.