I am having similar issues, but I dont know where to start. My engine had a miss at idle speed, so I had a tune up done with new plugs and wires etc. A few days later, my ac/ heat would only blow out floor and defroster. Now the engine idles so rough I dread stoping at a light in town. I noticed that my lights werent lit up on my 4WD buttons this morning, so i tried it just to see what happened. I only hear a clicking sound in the dash area. I am researching and Ive come across a few different possibilities. Could it be a clogged egr valve causing the whole problem or more likely a vacuum leak or actuator?? Please help. I know a little bit about cars but I cant afford to take it in and I really like my blazer. Any help would be appreciated.

 

it could be both. if your egr is clogged it will idle low and sound like its got a high performance cam in it. do you have the engine light on? and check your vacuum lines for dry cracking or leaks escpecially if the truck is around 10 yrs old....and replace as neccessary