remove it an clean the surfaces of lead and were it bolts to also the oil pressure switch will not be the cause of your starting or boost problem but possibly of your oil light the lambda should not be the cause as dont think the ecu uses that until engine is warmer were the coil packs 2nd hand if so they could be your problem an also depending on type of plugs they may need gapping to 0.6 (i may be wrong but sure iv heard that somewere before)