1994 Honda Accord Engine power drops when clutched down

I drive a 1994 Honda accord, recently its takes like two to three attempts to start my car in the morning and it seems to idle well when started, but when drivien into the highway I observe that my engine rpm suddenly drops below the 900-1000 stable value when ever I clutch down to move either to a lower or higher gear, this experience is worsened if I have the car A/C on while driving. Please what could be the likely cause.