I have 05 TL automatic with 220k miles, and just recently started having an issue with my RPM dropping at a stop light (with AC on). Dips to a bit below 500, car shakes, then hops back up and settles to around 700. Feels like it’s going to stall but doesn’t quite get there. Cleaned my MAP sensor hoping that would fix the issue but didn’t. I’ve read many threads on here but many different, and no definitive answers. I’m not sure where to start, vacuum hose leak maybe? Haven’t had any services done recently. I’ve read torque converter, my friend said maybe crankshaft position sensor, also I’ve seen O2 sensor. Many different things and I’m not sure where to start. I’m not terribly mechanically inclined without a YouTube video so I’m hoping it’s an easy fix I can diagnose myself, or with you guys. Also no error lights on the dash. Any help would be greatly appreciated.

 

vacuum leak.

you need to search for your specific leak.
look at the back of your intake manifold, follow all ports and hoses to find the broken hose or missing/unconnected hoses.

 

Okay I’ll start there. Hopefully something sticks out to me. Thank you and I’ll be sure to report back.

 

Check the EGR valve.
I experienced the same idling problem for a week before the CEL and code appeared. The EGR valve was dirty.