Corolla RPM moving down (shakes) when AC on

Question

I have 2018 Corolla XSE at 55000 miles. I recently started driving long range on highways and using the AC constantly. I noticed that when I come to red light/stop, RPM Lowers down than normal, and the car shakes a little bit. Same thing happens when RPM goes up. But shaking is felt more when it goes down.

Took the car to mechanic, he said first step would be replacing the AC Compressor, because there can be shortage. I wanted to get an opinion before going forward with it.

Edit: It does not only happen when AC is on.

Answer 1

When you find a mechanic who knows how to diagnose problems and not just line his pockets at your expense, they will check the engine for codes and pending codes and will have a look at long and short term fuel trim numbers. If nothing unusual shows up, they might want to clean the throttle body, because if it's not hospital-room clean, the car won't idle right and that may cause the engine to shake.

I would allow the throttle body to be cleaned as part of the diagnostic procedure because it's hard to know if it's really clean if it just looks sort-of clean.

Before you allow a mechanic to replace any parts, get it in writing that replacing the parts will repair the issue. Any mechanic who is unwilling to guarantee his diagnosis is just guessing, not diagnosing.

Just remember, diagnosis is not free, it takes time and mechanics deserve to be paid for their time.