04 regal elctrical concern/drivability

working on a 2004 buick regal 4dr with 3.8ltr. the starter screeches badly, but starts after a couple tries. however when car is running the dash warning lights cycle on and off, also the engine idle surges up and down...
installed new upper intake plenum and spark plugs and the car ran/idled fine until i went for a drive and started acting up again with same problem. turned the emergency flashers on and dash lights quit blinking and the engine surge went away....... turn flashers off and problem returns. any ideas are greatly appreciated. thanks

Did the vehicle come in for a no start, or because it was leaking coolant and you found the upper plenum leaking?

If yes, check the "Nose" of the starter....have seen cases where the coolant leaked into the cylinders, hydrolocking the engine and causing the nose of the starter to crack/break.....

As for that electrical problem, was it there before the work was done?

the dash warning lights flashing and the idle surge was the original concern. found engine coolant was low in radiator, so installed new upper plenum and gaskets including new spark plugs. started vehicle and run/idled fine.(for at least 15min) went to test drive vehicle and made it about 50yds and lights began flashing and engine started to surge just as before........ was told that it could be a problem with ignition switch/wiring..?. possibly losing a ground, but finding ground when flashers are turned on..?....

Checked battery cable connections?

Checked for codes?

It sounds like the ignition switch/harness assembly. See link below I posted last year for R&R procedure.

Ignition Switch Replacement (http://www.automotiveforums.com/vbulletin/showthread.php?t=1054152)

I had one, where so much coolant leaked into the cylinders, it filled the exhaust with coolant......car started, and when I went around a corner started to buck, idle went crazy and lights flashed because of poor idle and then it died....noticed fluid coming out of exhaust....jacked up the front end.....let coolant out....and then started ok....

found the problem to be the ignition switch/wiring harness. (dealership had 5 of them on the shelf, thats usually a sign of a problem part). removed and replaced it and the car runs perfect. thanks to all that replied......