I have been scouring the internet now for months trying to figure out my problem and I've looked at every article on this forum to try and pinpoint it. I think I've finally figured it out and I thought I would share.

First my problem:

2000 blazer ZR2 with 170k on the clock. When I first got it, it had a hesitation problem when starting cold. It would start fine but, when you hit the gas it would stutter. When I drove it, it would stutter until it got to 2nd gear and then it would go away. Once it was at normal temp. It would run fine. No stutter on startup or driving.

If I left it over night, same problem in the morning. At the time, this was a third vehicle (my toy). Then the Company truck left and I had to start driving it daily. After about a week, the problem went away entirely.

Well, I got laid off in early Jan (happy new year!) and the problem came back after leaving the truck sit for a few days and then having to go somewhere.

My Research:

Every article I read said replace the fuel pump. And I was about to do that. But, as I thought about it, my problem seemed temperature/ use sensitive.
A fuel pump doesn't seem to have a "predictable" problem curve. ie when it warms up, it goes away. It's either intermittant or a downhill slide to failure. No one seemed to think about the fuel pressure regulator. Nor could anyone tell me how it works specifically. All I found was it regulates fuel into the metering body.

Well, I just found this on JaguarForum.com:
Pressure Regulator - designed to permit fuel to return to the fuel tank depending upon engine RPM. Typically mounted downstream of the fuel injectors and part of the injector fuel rail system and operated by vacuum and/or electronic controls that operate a diaphram against a spring to regulate fuel return to the fuel tank. The more vacuum (to wide open throttle), the less fuel permitteed to flow to the tank. Conversely, with less throttle (idle), more fuel is permitted to return to the tank. The fuel pump is somewhat constant in its pressure and flow performance.

My FPR is located right underneath the air plenum. Which was also a bitch to find. It's a $50 part from Autozone and It will probably take about 2 hrs.

I'll report back and Let you know what happens! Wish me luck!

 

Testing the fuel pressure per the fuel system diagnosis article in the Tech Article (DIY) section (and linked to in my signature below) will tell you, definitively, where your problem is. Before you go through the trouble of replacing the FPR, wouldn't it be good to actually prove that it is the failed component?

 

When I saw the heading the 1st thing that popped into my head was the MAF <--- personal experience there. Have you cleaned it, made sure the wires are good & connection? Another thing was the intake temp sensor which works in conjunction with the MAF. With it being a seemingly intermittent issue with (possible) temperature issues/influences I'd consider a wiring connection/fault as well.