When my GX comes to a complete stop at traffic light for example, I notice that the revs fluctuate from 700/600 RPM down to 500. At the 500 mark the engine feels kind of rough and when it becomes smooth again when it goes up to 6 or 700. Any idea what may be causing this and what I can do to fix?

 

How often does it change while you're stopped?

It's normal for RPMs to change when the A/C compressor kicks in.

Chip H.

 

It fluctuates like every 10-15 seconds, and maybe it is because of the A/C compressor kicking in since I always leave it on. But that rough vibration for a Lexus does not feel right - and it started to happen like a month or so ago. I recently got timing belt/water pump replaced but did not notice it immediately - maybe after couple of weeks. Spark plugs and transmission fluid were changed at 120k and I'm at 180k now. All oxygen sensors were replaced like 10k miles back. I always get top tier 93 gas and also add additives every now and then. Maybe I should also check air filter which I think was replaced about 10-15k miles back.

I searched online, and someone mentioned possibility of vacuum leak. How do I check for that?