i have 94 e420 i check the codes an i came up with 6 idle speed control, 17 data exchange, 19 fuel injectors, 20 speed signal. how do i clear or what should i do to clear these codes

"Search" > "Advanced" function:

"Turn ignition on, press switch 2-4 secs, and count the number of flashes. After reading that code, press 2-4 seconds to read the next code, and continue iterating until all codes are read. You'll know all codes are read when you read the first code again. One flash means there are no codes to read."

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'84 300SD sold
124.128

that is what i done howdo i erase the codes or fix them

Next step is to erase them and see if they come back. Hold down the button for 8-10 seconds to erase each one. It's important not to abbreviate too much, e.g. code 19 is more likely "system adaptation at limit" - try a search for code 19 and JimF's chip to resolve. Code 6 is telling you to read the faults on pin 7. Code 20 is saying your speedo is/was broken or disconnected. But first erase, drive the car and worry only about the codess that come back.