Car stutters at stoplights lexus ls400 1990

Tune up items, coil/module, coolant temp sensor, many others too.

Could be Is run to rich. You can have it tested on a machine at your local garage. Or you can try using Gas treatment or fuel injection cleaner to see if that helps. ever witch one you have.

Could be a transmission problem or something as simple as bad spark plugs.
The engine is under the most load when RPM is low and you are trying to accelerate, such as when it upshifts.
You should have the computer checked for trouble codes and hopefully that will point you in the right direction to test.
If the spark plugs have more than 50,000 miles of wear you might start with replacing them.

Check the front O2 sensor. I had a 99 Jeep that would stutter and seem to lose power while accelerating. No check engine light came on but took it to a shop and had them put it on a computer. Come to find out that the O2 sensor was giving the engine misreads and was telling the engine to take in more fuel. Causing one of the cylinders to misfire.

No engine codes?
Check the spark plugs & plug wires first. Then check ignition coil/distributor cap.

if you went the route of changing the plugs, try the spark plug wires, and the distibutor cap

Try unplugging your Mass Air Flow Sensor (MAFS) - you'll find it on top of the metal body immediately after the air filter. I went through an 18 month ordeal - replaced fuel filter, fuel pump, dropped fuel tank and cleaned it, ran 55 gallons of fuel injector cleaner through the system - nothing! After reading some blogs on this car/engine, gave the MAFS unplug trick a try. The car instantly corrected itself (when you unplug this sensor, the engine control module reverts to factory default, allows sufficient fuel into the engine for unitterupted performance.) However, if this corrects your problem, it's only a temporary fix. Run it about 3 days - it you notice soot in the tailpipe, the factory default is running too rich. Replace the MAFS.

give it a tune up and change the fuel filter!!!

My was doing the same thing, it was an EGR valve and a misfire on the #2 cylinder which required a new spark plug and a coil pack
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Turning off the CEL does not cure any problem, you have a ignition miss, U will have to have it put on a diagnostic machine to determine the cause of the miss.