My car has to strain to pick up speed after being idle at a light

if it starts and runs wont be
timing marks or crank angle sensor
or coils

any engine check light on ?
could be the air idle sensor
egr
fuel pump pressure to the rail

Check for vacuum leaks would be my first thought.

Check engine light on? Check the trouble codes.

Idle air control (IAC) stepper motor stuck, dead or carboned up.

Low coolant will increase idle speed if a sensor is uncovered. Makes the computer think the car is running hot.

You don't say how many miles its done so is it due a good engine service? Its no good sticking it on a diagnostic unit if its already sick. Get the basics done first.

sounds like u cld be dumping fuel! Go to repair shop to get a diagnostic checkup!!! Couldn't hurt!!

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

Observe if you go down to the first gear when you slow down and pick up speed after. It may be an issue with the torque converter. If you have rough idling , you may have a dirty or faulty IAC valve.

Read the trouble codes for your automatic transmission using a scan tool. I like the wireless ELM327 OBD2 adapter and OBD Fusion app.
The trouble codes will tell you why the transmissiion is putting the car in limp mode.

have the car scanned for the codes,then get back to me,most big chain parts stores will do this for no charge

speed sensor

1993 Lexus LS400 wont idle but will run