I have a 2001 blazer w/ 4.3 Vortec vin code "w" engine. I had to replace the lower intake gasket and found the timing chain cover leaking. after pulling engine and replacing the timing chain and cover gasket, oil pan gasket, plugs, wires, cap, and rotor. and putting it all back together I have a rough idle it will idle about 900 to 1000 rpms then drop to about 500 sometimes it will stall completely, also sluggish sometimes accelerating but once I get I get rpm's up it runs fine. I am also getting the SES light on had the parts store use their scan tool it shows two codes p0300 and I believe the other one was p0507 I had one person say it sounds like a vacuum leak but I checked the lines they all appear good and when I pulled the two vacuum lines from the engine individualy the rpm Increased.

Did I do something wrong, or am I just missing a step somewhere?

I did use all AC Delco parts for the ignition.

 

Check your EGR to make sure it's sealed and not stuck open.

 

update I reset the codes, it still runs rough at idle. Thought maybe the codes were from problems I had getting it to start and the distributer not being clocked correctly and after driving it about a week or so had the codes checked only one showing is P0171.

 

another update after trying multiple things to rule out a vacuum leak or pcv system leak causing problems, on a whim I tried disconnecting the mass airflow sensor. When it is disconnected the Eng idles great, but if I plug it back in it idles rough. Does that mean that the mass airflow sensor itself is bad, or that something else is bad that is effected by that sensor?

 

Also note I did try cleaning the sensor using the mass airflow sensor cleaning stuff. I heard that if you use carb or brake cleaner it will mess it up.

 

Other cleaners can mess up the elements inside that it uses to read. If cleaning didn't help, the MAF sensor probably died. Or for another reason it is not reading correctly.