i have an 08 tsx and noticed that whenever i first start the car, it does this slightly noticeable rhythmic vibration that appears to happen in cycles, which appears to go away or at least isn't so noticeable after driving for a while. i guess to better describe what this feels like it's as if someone moderately shakes your chair as you sit in it for approx 2 seconds and then less than 30 seconds later, shakes you again for another 2 seconds. is this cause for concern? what could cause this? hope i described it well thanks for any input!

 

This is normal. It's very likely coinciding with cycling of the AC compressor. Once the engine reaches operating temperature it runs more smoothly. Before that it runs slightly rich and with the timing retarded. Nothing to be concerned about.

 

Try starting with the HVAC off for the first 90 seconds or more. Sounds like that would confirm LukeaTron's diagnosis.

I do, and find that my 2006 5AT engine starts up smoothly, and gives good power in the first few minutes. I know the heater/blower doesn't operate at normal speed until the air is cooled/warmed to the climate control set temperature, so most days, I just don't use climate control for the first 2-3 minutes of driving. When I do need a/c right off the bat, generally I've just turned the car off within 60 minutes, so I'm not so concerned about "cold engine" syndrome.