1989 240DL JETRONICS 2.4 HAD A RUN AWAY ENGINE PROBLEM. REPLACED THE ECU MAIN COMPUTER WITH A JUNK YARD ONE OF THE SAME NUMBER. MY CAR STILL IDLES FAST HALF OF THE TIME. UNPLUG THE INTAKE HOSE TO THE AIR CONTROL VALVE AND PLUG IT AND THE CAR IDLES FINE. VALVE HAS BEEN CLEANED, WORKS FINE, NO BINDING. 8 OHMS ACROSS THE TWO TERMINALS. I BELIEVE IT IS THE SIGNAL CONTROLLING IT, ALTHOUGH I HAVE NOT DONE A THOROUGH CHECK OF THE WIRING HARNESS YET. AFTER ALL OF THAT THE QUESTION IS - THE BLACK COMPUTER BOX ABOVE THE PASSENGER'S FEET ON THE FRONT WALL. WHAT DOES IT DO? DOES IT AFFECT THE IDLE CONTROL SYSTEM? ?????? NO MECHANICAL BINDING OF THE AIR VLAVE, LINKAGE, ETC. ALL ADJUSTED SAT.