Engine Vibration at Low RPM?

So I noticed since I test drove the truck that at low RPM, like when the brake is on and I am stopped, the truck vibrates ever so slightly. Runs smooth as can be once I get rolling, but around the 500 RPM range it is a bit shaky. I figured it wouldn't be a big deal to fix, if it was even a problem. It is only noticeable enough to bother me, not enough to cause me any real problems. I noticed, though that when I turn the AC off, and the RPM bumps up to about 900, no more vibration/shakiness. Turn AC back on, RPM drops to around 500 again and it vibrates. Any ideas fellas? Run some SeaFoam through it or...?
-EDIT- AC on when driving, no vibrations, only vibrates when stopped, so I don't think it is the AC compressor.

 

mine does the same thing. I have a load of miles on mine and I figure maybe get injectors professionally cleaned, replace plugs, maybe plug wires, clean throttle body, clean MAS...if that doesn't do it, I'm probably looking at a loss of compression in a cylinder or two. I'm not really worried. Mine doesn't die...just a little shaky when she drops down in idle. Same thing here...turn on air, smooths right out

 

Well I don't know if this is the right answer but there is a reason that your AC in your house costs so much to run. It uses a lot of energy to operate therefore costs money to use. The same can be said in an engine with your vehicles AC. When you use it, it uses a significant amount of energy, which costs you fuel. When you press the AC button it disengages a clutch on the compressor in your engine giving your belt system the full load of that compressor which puts an extra load on your engine and your idle doesn't account for that. I haven't seen this myself because mine doesn't have a tach but I know that i had a seized idler pulley and i freed it and ever since then my gas milage has gone up about 1 mpg.

More load, same gas and air, less rotations

Just something to think about

 

You missed the OP point here. His tacoma is not idling as smooth as he would like or expect. When you turn on the AC or Defroster, the computer tells the IAC to up the idle to support the extra load. All we are both saying is that when that happens, the idle smooths out. It’s like there is a problem with our motors because they won’t idle smooth around 500 rpm. Kick up the idle with the gas pedal or AC/Defroster and it smooths right out. That’s all. We’re just trying to figure it out.

 

Oh, I see what you're getting at. Mine has the exact same problem
Apologies on the somewhat smartass response

 

No worries. Its not a big deal, the vibration, it is just an annoying little thing, but I'm sure I will get used to it over time.

 

Ever try cleaning the throttle body? How are the plugs? Also carbon deposits in the engine can cause that, try a nice cleaner like

$25 bg44k BG 44K fuel system cleaner power enhancer 11oz.

bg44k

 

I like low idle. it rumbles deeper

but seriously, I think it's more of a 1st gen thing. I've been in at least three with the same rough idle. they're designed to last forever, not idle like a Porsche

 

On my 2.7L truck, when at idle, when I TURN ON the A/C, the computer INCREASES the idle to allow for the extra load of the compressor. According to your first post, the idle drops. That needs to be corrected. What is a normal idle for a 3.4L?

 

My 3.4l idles right around 700 with AC on and 500 with it off. As stated i would do a tune up. Plugs, wires, air filter, clean MAF and run a can of Greased lightning fuel treatment through it. Most people never clean the MAF sensor and that could make a big difference.