4.6 intech erradic slight erradic idle. tach

Could be the tach isn't accurate at low rpm, that isn't unusual. Try connecting an external tach for testing.

run the fault codes
check for vacuum leaks on all vacuum hoses
check fuel pressure
use quality injector cleaner

The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). The engine should pick up speed and begin to smooth out.

The battery has nothing to do with the idle speed

go to auto zone,its free ck.throtle senser

It's been almost 2 years since you posted the question so it's likely you will not see my answer to your question.

First, do NOT make any adjustments to your throttle body idle setting. The screw most likely never budged since 2006 so you should not touch it since this is not the root cause. But yes it is wise to check all vacuum lines as "craig" suggested.

I have a 2007 Corolla CE, 1.8 liter VVT engine, 5 speed manual transmission which I bought new from the dealer. Currently has about 108k miles on it. After about 4 or 5 years in cool to cold weather it started doing the same thing. I researched it online then asked my local Advance Auto Parts person who confirmed my hunch. It is known as "idle hunting" when the engine is cold, in colder outside temperatures the idle rpm's will increase up to roughly 2000 rpm then drop to idle, then back to 2000 rpm, then repeats multiple times. Then after driving a short distance, stopping and running at idle, the idle speed may drop to 600 or 500 or as low as 400 rpm, running quite roughly but still keeps running. My Corolla normally idles smoothly and steadily at 800 rpm when warm or hot. The idle hunting or low idle rpm will typically correct itself when the engine warms up enough.

The problem: the intake manifold gasket has aged and shrunk a bit, allowing engine compartment air to get pulled directly past the gasket and into the cylinder head intake port. This causes an imbalance between the reduced air filter airflow sensed by the Mass AirFlow (MAF) sensor versus the actual air/fuel ratio versus the engine rpm versus the oxygen level in the exhaust stream. The gasket will shrink more as the temperature under the hood drops, allowing more air to flow past the gasket. The Engine Control Unit (ECU) is simply trying to do its job as programmed by increasing fuel delivery to compensate for the overall imbalance, then when rpm's get too high it will reduce fuel delivery.

The solution: purchase a new intake manifold gasket for roughly $10 to replace the stock gasket. Mine is a thin orange polymer gasket with round cross-section which seals around all 4 intake ports. You can search for instructional video of how to install it on YouTube.

I purchased one but did not install it yet. I am sure this will resolve the problem since all other suggested fixes I found on the internet did nothing but unnecessarily frustrate the owners.

Possible Idle air control, simple to change on the throttle body

have you checked the EGR (exhaist gas recirculation) valve? sometimes carbon will chip off and make them stick partially open causing extremely rough idle or wont idle at all without help from throttle

run a fuel pressure test, if that checks out fine it may be a faulty coil pack or ignition control module

this sounds similar to a problem i had. as the rpm went over 2000 the engine would stop for a split second and then kick back in.
after a few days looking my garage finally found the problem was a faulty air mass meter.
this cost me £200 in total to be repaired.

Check the fuel system, chenge fuel filter. clean the fuel tank.