Hey,
I have a 2007 Volvo S40 2.4i with 154k miles. Recently it has developed a terrible idle especially when cold, coming to a stop, or while stopped at a light and letting off the brake. The whole car shakes and makes a very obnoxious bum bum bum noise and it seems like it's going to stall and urges forward. It doesn't matter if it is in park, reverse, neutral, or drive, the idle is still rough. It seems to go away while driving and runs completely normal. I just thoroughly cleaned the throttle body and I appear to have no vacuum leaks. Has anyone had this problem or have any ideas on what it might be? I just replaced the MAF sensor with oem part, and have even used diagnostics tools to run tests and nothing is coming back relating to this issue. Thanks a lot.

 

rough idle is saying you have a fuel trim issue. Could be the fuel pressure, could be the spark, could be the air metering (think intake air leaks). On the subject of air leaks, you can't visually see all the vacuum lines so a smoke test may be in order. Also there's devices like the PCV oil separator which can fail and create the air leak, or you could have a cracked boot or a bad seal etc.