I have been having a rough idle problem. Along with hard starts and 14mpg average. The check engine light has been coming on with p0300, (p0306,p0302 occasional) when idling. And p0175 when driving. Things I have done are changed all o2 sensors, new air filter, cleaned MAF.
The freeze frame data shows the ltft being at -14 to -30 and the stft has been close but recently been at 0 with the ltft bank 2 -18
Any Suggestion?

 

First and foremost... What are you working on?

When was the last time a tune up was done and what brand of parts were used?

Have you ran any injector cleaner through it?

What made you replace all of the O2 sensors?

P0175 - Fuel Trim System Rich Bank 2
P030x - Random/Multiple Cylinder Misfire Detected

Any vacuum leaks near the driver side of the intake manifold and/or exhaust leaks on the passenger side bank?

 

Sorry about that, It's a 96 blazer 4.3 engine code W. I ran seafoam through on the last fill up. I changed the o2 sensors because of the strong cat smell I had , and a friend gave me 2.
The last tune up.. when I first got the blazer in '04
Other than the mpg I haven't had any issues with the reliability of the rig.
I haven't checked for vacuum leaks, but did use a vacuum gauge and it was fine.

Any thoughts on the fuel pressure regulator? I'm debating on taking it somewhere or buying a fuel pressure gauge.

 

Your truck has 4 O2 sensors. Which 2 did you change? Hopefully the ones closest to the exhaust manifolds in the Y-pipe.

A fuel pressure and leak down test will tell you whether you have a fuel supply issue.

A partially clogged catalytic converter could also be adding to the problem.

 

I changed all 4, the reason was I smelled the cat and a friend had 2 brand new for free

 

The O2 sensor directly ahead of and then directly behind the cat have nothing to do with fuel management in the engine. So those were replaced unnecessarily.

Unless you had an O2 sensor code, I doubt they were the reason for the smelly cat...

It may be time to do a full tune up again. At the very least, you should pull the plugs and see how clean the cylinders are burning.