My '00 Jimmy with 114k miles has developed a really annoying habit. When I crank her up in the morning or after she's been sitting for more than 5-6 hours, she stumbles and misfires until she is fully warmed up. It runs a little better at full throttle, but when you level out the throttle to cruise she misses again. The check engine codes have indicated "multiple misfire", and "bank 1 too lean".
I have replaced the MAF, spark plugs/wires, and cap/rotor. The problem is definitely temperature related. Like I said, she runs fine once up to temp. Is there a possibility the fuel pressure regulator can be the problem? I'm thinking the unit may expand and shrink with temperature changes. Just a thought.
Please help if you can!

 

have you tried replacing the 02 sensors?

 

i had a 1996 burban that had the same symptoms and it was the o2 senosor bank 2 sensor 2

 

I replaced the driver's side sensor, the one before the cat. I believe thats bank1 sensor1. This mornin' she did pretty much the same thing. Ugh, is there another sensor up closer to the manifold? Ive seen no exhaust leaks, maybe its the cat?

 

look after the cat their should be another sesor ofter the cat. the first sensor should be fairly close to the manifold. im not sure how many sensors your blazer has but i know some vehicles have as many as 4.

 

Hmm. I will try replacing the other behind the cat. I cant find a vacuum leak either so if that doesnt fix er' then I'll have to start back at square one.

 

Did you have it hooked up to a scanner and check the live data on the o2 sensors, or due a fuel pressure test should be around 60lbs of pressure if it drops off then a possible leak at the regulator. How is it at idel if it's very ruff almost stalling then clean the EGR valve