1991 PLYMOUTH VOYGER 3.0. 200,000MILES.REPLACE THE ENGINE WITH A USED ENGINE UNDER 30,000 MILES. HAD TO USED MY INJECTOR OFF MY ENGINE. IT RAN GOOD. BUT THEN STARTED ROUGH IDLING AND SUCKING AIR ON START UP ONLY.BUT THEN IDLE GOOD. ALL START UP. SOMETIME WHEN BRAKING IDLE LOW THEN NORMAL.CHECK AND RECHECK.STILL .THANKS