1990 Lexus LS 400 Check engine

You need some punctuation in that huge sentence so it makes sense. When the Check Engine light turns on, it means the Engine Computer detected a problem, set a diagnostic fault code, and turned the light on to tell you. I'm not sure why you wouldn't trust your mechanic to read the codes. It's not like he's going to be able to fix anything by not telling what codes are set. If you don't believe what your computer told him, many auto parts stores will read engine codes for free, but be aware they're in the business of selling parts. Fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition.

Once you know the code numbers, come back here and post them. We have listings of the descriptions for each one, and I can suggest a course of action for most of them.

Not a bother. We're here to help, but you didn't provide anything to use to make a diagnosis. We need fault code numbers, test results, observations, or something to work with. What kind of help are you looking for?