I have an 01 blazer that idle a little rough at a red light then when park is engaged it idles much rougher and makes a loud humming noise. I already replaced these things on the truck so far, Fuel pump, spark plugs, spark plug wires, cleaned out throttle body, throttle body gasket, synthetic oil change with oil filter, cleaned out iac valve. I've tried everything someone please help this is driving me crazy haha.

 

Hello Adub,

A little more info/history on your truck would be helpful.
Miles on your truck? When did you purchase?
Any Codes?

It looks like you are doing the good maintenance.
The buzzing noise could be a vacuum leak?
Injectors under your manifold? Just guessing.
Clean the MAF, Clean the EGR.

Add a little more info/history and someone will lead
you in the right direction to figure it out.

Lots of good help here with more detail on your part.

Thanks - Mark K

 

I figured that was enough information but here's some more on the truck, I just bought it three months ago from a used dealership, it is an 01 and had 127,000k on it there are no lights on the truck and I ran the computer for codes and absolutely nothing which leads me to believe that it could have something to do with the exhaust although it is not loud while driving. I will try cleaning out the egr valve and the things you mentioned but I know if is not a major problem and does not affect the performance but is rather annoying when parked or like I said stopped at a light, lately it really hasn't been that noisy when stopped at a light but once park is engaged it goes to that loud humming noise. I really don't think it's a vacuum leak though like I said there were no codes that came up but they could be on their way. If you need nah more additional information let me know.

 

It was the pcv valve