500SL rough idle

Having rough idle trouble on a 92 500SL. Changed plugs and resistors, checked for fuel and vacuum leaks, replaced o2 sensor.
Duty cycle at 50% at start up, then increases to 93% after warmup. ASR light comes on intermittenly. I also set a code 18 when I unplugged the idle air valve( How do I reset?) The roughness can also be felt when I increase engine rpm's. Any suggestions are certainly appreciated. Thanks....