For the past week or so I've noticed an issue with my 06TL 6MT (20k miles). At idle, say sitting at a light, it will occasionally drop 100 to 200 rpm for a second or two and then come back to idle. When it does this the engine note changes alittle - kinda like what is sounds like when you slightly lug the engine. I also noticed this when I first engage the clutch when approaching a red light. As the rpms start to drop with the clutch in, they will drop a little below idle and then come right back up.

Has anyone else noticed this with their 6MT? The only thing I can think of is that I started running the A/C this week. But I don't remember this happening last summer. Or maybe I got a bad tank of gas?

I have a regular maintainance appt. scheduled for Tuesday. Should I point this out or am I just being oversensitive?

 

why don't you turn off the a/c and see if it's still doing it?

my money is on the a/c.

 

But is it okay that it does it with A/C on?

 

I can feel it when my a/c kicks in. My RPM does change.

I don't know in your situation. But if you do that you will know if this rpm drop is a/c related or not.

 

Only when it first kicks in? I could understand that but mine is doing it two to three times at any given red light.

I'll see what happens with the A/C off.

 

no... as you said, 2 to 3 times at any given red light for me as well.

 

man I never use A/C..... A/C hurts performance! LOL I'm gonna try to drive without A/C in the summer...

 

A few things to consider. First off, how many miles do you have on your car?

The quality and brand of the fuel you use can cause this problem. My 2001 Ranger pickup (2.5L 4-banger) does what you describe quite a bit more when using Mobil then when using Amoco (BP).

Another thing that can lead to this is a dirty throttle body valve or injectors in need of a cleaning. It's simple to check the condition of the throttle valve in the throttle body. Just remove the ribbed coupling and using a flashlight, open the valve (also called a butterfly valve) and check the valve seats iin the throttle body opening (of course, do this with the engine off). Using a quality throttle body cleaner, coat a shop rag and clean the seats.

As for a good fuel system cleaner, there are many. I use Chevron Techron Fuel System cleaner every 10,000 miles.

Generally, the A/C will not cause this problem by itself since the ECU compensates for the additional load. So I suspect the problem is elsewhere.

 

The car has 20k miles on it and I rarely run anything other than BP/Amoco 93 Octane.

 

Ok I checked and it is only doing this with the A/C on.

 

This is false... generally, the ECU is reactive only (as opposed to proactive) when it comes to compensating for the additional load of the compressor. The TL's compressor, like some cars, cycles through periods of being engaged and disengaged as required to cool the incoming air to a sufficiently cold temperature. When the compressor engages, the additional load on the engine causes the RPMs to briefly drop. The ECU detects a drop in RPM and adjusts accordingly to bring the idle back to spec.

I'm not surprised. This is normal. On every manual car I've driven, I can easily tell when the AC is on because of the bouncy idle and the noticeable drop in overall power. Can't do anything about it but live with it.