Sometimes when my wipers are on, they will slam into the plastic cowl piece as they go down. When the wipers are turned on they are supposed to rise up off that piece a few inches and stay off of it until they are completely turned off. This problem happens about 60% of the time they are on, and the rest of the time the wipers act normal. What do you think this could be??

 

Check the nuts that hold the wipers down and make sure they are tight. You can pop off the little cover at the base of the wiper arm to get access to the nut.

However, when mine were loose, the driver's side wiper would flip off the windshield and end up landing on the driver's side mirror. If tightening the nuts doesn't help, you may have to replace the wiper motor itself.

 

i had the same problem my wipers would hit the cowl and then go super high on the window too on the drivers side it would almost go off the windshield. My blades didn't wipe the window completely on the pass. side either because they were cheap aftermarket heads. I went to a salvage yard and got GM wipers and heads and then i got a new motor. I put them both on and it fixed all my wiper problems.

 

I also had the same problem and I took my wiper motor out to find that there are 2 rubber grommets that hold the front of the wiper motor in the cowl. They Both were worn out. After I replaced them, it fixed the problem.