I have an 03 blazer 4wd. I just recently changed the fuel pump and the fuel filter. Now the engine runs rough while at idle. Driving is fine. The engine stalled once or twice but not many times. It is coding p0171 and p0174 both banks running lean. I have checked the air intake and it is all hooked up properly. What could it be?

 

Vacuum leak?

 

Big vacuum leak?

 

Where?

 

get a fuel pressure gauge and tell us what it reads as I had an 05 Trailblazer that would throw a P0171 code until I changed the fuel pump. Yes, I saw you changed yours but if you can't hear a vacuum leak I would look fuel pressure'

 

O2 sensors maybe? I'm about to do mine tomorrow. Bought this blazer, idled rough and smelled like it was running rich. Previous owner said it just needed an o2 sensor. I decided to give it a full tune up as well. Good thing too because there were Autolite plugs in it, and the cap and rotor were a little worn. I'll know tomorrow if all of the work was worth it. Hope you figured out your issue...

 

I've come to the conclusion after a ton of research that my issue is a fuel pressure regulator. I'm hoping to get it done Monday afternoon or Tuesday. If it still has issues, I'd think about selling it off or getting another one and using it for parts. Never took the throttle body and intake plenum off of one of these, any tips? Thanks.

 

Wild thing taking off and cleaning the throttle body is something that can be done in about 45 minutes or less. I just did one of my trucks and there was carbon build up that resembled bed liner in there. I took out the IAC valve as it drop from 600 rpm to 200 rpm at idle. Pay special attention to edge of the plate and where it moves.

Truck runs much better now. Also I've had good luck with BG44k fuel injector cleaner. It really reduced the carbon that was causing a severe miss on my son's ZR2. It has leakage past intake valve #4.

 

I just did about 90% of the job, you were correct about the throttle body being gummed up, it was like wet bed liner as you said. Once I got the plenum off, it was obvious that the regulator was the issue as everything but the rear two intake ports were covered in that sludge. So I swapped in a new one, and got as far as I could reinstalling everything. I need to make a trip to the parts store for a few small things, then I can finish putting it back together. I'm hoping this fixes the issue it was having, I should know by this time tomorrow.
I can tell by the few things I've done to it so far that this thing hasn't been very well maintained at all, so little by little I'll get her back to her original glory. ☺

 

Got everything buttoned up, started it up, ran at high idle for a little bit, I discovered I didn't install a vacuum fitting right, checked all the other bolts for the plenum and throttle, all ok. Took it for a ride, ran beautiful. Filled it up with gas and changed oil. A couple hours go by and my mom calls and has a flat tire while on her mail route. So the first rescue mission was a success, didn't miss a beat.