I had to replace the battery on my 2006 4 cylinder. After I replaced it and I cranked it it began idling too low. It idles at about 500 and then to 750 when I push on the accelerator. If I push too hard on the accelerator it drops back down to 500. What could be causing that?

Did you check for codes before you began replacing parts ? Have you replaced fuel filter ?

You most likely have a cylinder mis-fire. Usually a bad spark plug or ignition coil/ignition wire. Check the codes to determine what cylinder is causing the misfire and repair a necessary

Hello, the idle speed is controlled by the computer, there is no adjustment, what you can do is to clean the inside of the throttle body:

Remove the intake hose from the T/Body, disconnect the battery, use a can of air intake/throttle body cleaner and a brush, open the throttle all the way and clean the carbon out, put the hose back and reconnect the battery, start the engine and keep the rpm up until it clears out, drive it for about 15 minutes, about 90% of the time this fixes low idle.

Low compression does not require head removal. Do a compression test on a cylinder, then squirt some oil in the spark plug hole. Do the compression test on that cylinder again. If the compression goes up then the rings are worn. P0303 is a misfire in cylinder 3. This lets unburnt gas into the catalytic convertor. The cat can overheat, melt and be ruined. If the check engine light is blinking don't drive the car. A misfire is either no gas, no spark or low compression. The quivering light can be from idle or failing alternator. Put the probs of a multimeter on the battery posts. Set the meter to volts dc. Start the car the voltage should be between 13 and 14.6 volts. Anything more or less points to an alternator problem.

Replace the idle valve with a factory one and remove the negative battery negative cable for 5 minutes to reset the idle control system to base line settings.

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.

I am not sure about the exact idle required,but yes 500 is low.You should check the throttle position sensor next.If it is bad,it does not know how mauch gas you are using,nor how much is required.This is definitely a symptom of that.It also uses the TPS as an input to the engine computer which is 'telling' it to shut off.

Most often, dirty or faulty 02 sensors will throw off the idle. The 02 sensors and camshaft position sensor basically control all the idle. If TPS was dirty or bad, you would have some hesitation when giving some gas. Bad plug would cause lack of power or misfire.

Try cleaning your throttle body, then disconnect the battery to clear the memory.

THis has happened to me in the past. My fix was to clean the throttle body. The problem began after my battery died. The computer was defaulted back to its original settings after replacing the battery. Once I cleaned the throttle body, everything was fine. This happened at about 85,000 miles.