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This is a pretty straight forward question, but I have an 09 Camry 5-speed manual. It only has about 25k miles on it and has been regularly serviced.

However, as of late I've noticed that when I drop it into neutral and am standing still (at a red light for example) the entire car seems to rumble and I notice that the rev counter is dropping to about 300 to 400 RPM's.

Anybody have any idea what could be causing this?

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To clarify, sitting still while in drive it idles at normal speed, and smoothly, but in neutral the revs drop? – mac Aug 14 '12 at 16:00
@mac I'm sorry, I should have made this more clear in my post. It's a 5-Speed manual transmission, and the revs drop when I shift out of gear and into neutral. – Mick MacCallum Aug 14 '12 at 16:16
OK. So the car idles rough and low. On such a new car, the idle speed should be controlled by the computer, so something is not right here. No check engine light? – mac Aug 14 '12 at 16:35
@mac Nope no lights on, and I think that might have been the answer I was looking for. I should have assumed that would be computer controlled. Any idea if adjusting the idle on this thing is something I can do myself? – Mick MacCallum Aug 14 '12 at 17:09
I don't think that this is simply a case of the idle speed being "set wrong," (even if it were, you'd have to tinker with it by computer) I think there's a deeper problem here, which is why i asked about the check engine light. The car runs perfectly when you're moving? Not even a hint of hesitation or stumbling when your foot is on the gas? – mac Aug 14 '12 at 18:04
up vote 4 down vote accepted

The 4-cyl camry's of that vintage are known to have a rough idle, but a drop to 300-400 RPM at idle is pretty severe. I haven't seen the spec, but I would think that car should probably warm idle in the 800-900 RPM range.

You should have the car scanned to check for pending trouble codes. These codes can show up before the Check Engine Light (CEL) goes on, and they can be a huge diagnostic clue as to what's wrong. I'd expect to find something here if your problem is as severe as it sounds--the computer should have logged some misfires.

The generally accepted stuff to check for a "normal" rough idle would be

  • intake system: clean the throttle body and mass airflow sensor, check for vacuum leaks;
  • ignition system: spark plugs, wires, and ignition coil(s);
  • fuel system: injectors, filter;

In your case, I'd suspect something like a bad sensor or bad ignition coil--something that can really screw with the system profoundly.

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