rough idling and slugish movement

[joeabidakun]

ℓ̊ own a nissan frontier 2002. My mec did a service on it. Then it returnd with the ses light and the engine would give a tapping sound, then drop rpm during idle. My mec says ℓ̊ should change the plug distribution wire and all would be fine. ℓ̊ did change the wires and ran a scan. ℓ̊ got a fault code for knock sensor and a code for iacv. ℓ̊ took off the upper airintake manifold and cleaned the iacv and then install it back. ℓ̊ did another scan and all code was gone, but the engine stil drops in rpm and when on high way, the engine would slugishly increase in km/h and would increase quickly after a minute of two. And also black smoke on my tail pipe with clear water Please what else can ℓ̊ check to correct this.