Disconnected battery to clean post and now the car does not idle correctly. sometimes it stalls out.

Throttle position sensor or maf sensor malfunction.

Disconnecting the battery sometimes corrupts the CPU program and it takes the use of a scanner to reprogram it . What you have done sometimes fixes the fault but like all CPU programs it only takes one bit to throw out the program.

This is commonly caused by a dirty automatic idle speed control air bypass valve, it can be cleaned and correct the problem. Follow the instructions below exactly.

To correct this problem get a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, spray it into the air intake of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speeds problems you may need to seek the help of a professional.

this can be caused by and usually is a sludged up idle speed control valve, follow the instructions below to correct this
, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

the engine compensates for the load try turning up the idle screw also check the ignition system you might just need new wires and or cap rotor or your coil is bad also plugs

Won't idle after battery change... SOLVED! well, for me anyway. :)

I just experienced the same problem on my 2002 tundra last night, and fixed it this morning after sleeping on the problem. Here's how it went.
I cleaned the terminals, etc., and replaced the battery, as it was 7yo and old and on the verge of failing.
Immediately after this, the truck would start right up but the idle would drop to about 100 RPM, then slower and slower, and eventually stall. Every time.
I warmed it up and drove around the neighborhood for about 45 minutes, thinking the computer needed to re-learn it's Idle settings, etc... No change.
This morning, I decided to go after the cheap and easy fixes first...
Inspect throttle body... it was filthy full of black sticky dirty/sludgy stuff. I cleaned it off using a rag and some brake cleaner. DID NOT spray brake cleaner IN the opening; just on the rag and then wiped all of the gunk out of the opening, butterfly, and inside as far as my fingers would reach with the butterfly open.
Reassembled everything, started truck... runs perfectly.

Dead battery? Won't run? Dirty throttle body? How do these all tie together?! Here's why (to the best of my understanding).
Over the past 65k miles, dirt and gunk slowly but surely builds up in the throttle body. At some point, the computer senses that this affects the air/fuel mixture or something of this nature. The computer compensates for this, and stores it to it's memory. Sometime during the vehicles lifetime, the battery fails or is disconnected. The compensation settings that the computer stored are lost when the power is disconnected, so the next time the engine is started it's telling everything to behave as default... but the car isn't in a default state, there's **** in the throttle body... or a bad sensor, etc.
I could be way off, but my gut feeling is that this is correct. My advice: Pull the intake tube off the front of the engine and clean the gunk out of the throttle body. It should be the first thing to try, since it's the cheapest and easiest thing that I can think of.

Here is the most common cause of surges and stalls and low idle rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

Try cleaning the inside of the MAF sensor, the throttle valve and the idle speed control valve, then disconnect the battery for 5 minutes and drive for a day or two, this should correct the problem or make it better.

If the car starts after charging but will not idle, I would suspect the alternator is defective. The alternator is fitted with a diode pack (all to do with the electrics, valve bocking AC but allowing DC to pass) this is the the part that fails.
It allows a correct current to pass to the battery (DC only)
If the car starts after charging and runs for a few miles before stopping and the evidence is a dead battery - It will definately be the alternator.
Hope this helps

Clean the throttle valve and the air bypass idle speed control valve, they get full of sludge and restrict air flow, this causes a low idle at times and the engine will stall, clean them by spraying carb spray into the throttle valve while the eng is running, have someone hold the idle high or it will stall, after using at least 1/2 can shut down and disconnect the battery for 5 minutes, this clears the memory and allows the computer to relearn idle strategy, the computer willl take a few days to relearn the idle, maybe 30 miles of mixed driving.