Rough idle when below 1000 rpm.

[Ryan Heo]

Hi.The PCV valve, A/T pan gasket, and spark plug tube seal, which were all OEM parts, are replaced on today. After that everything is fine except for rough idle. I stared the engine to test overall but as the rpm gauge goes to 1000 when gear is P, I felt the engine is almost dead. It wasn't dead. So I checked under the hood, I can listen to strong vacuum sound. I thought some vacuum hoses were misconnected or missed. I check double it was everthing good. What could this kind of problem make for my car?Thanks.