Hello again! I finally finished replacing the head gaskets on my 94 s10 blazer 4.3L vin W, but now I'm having different problems, primarily that my blazer will start up but quickly die. It sounds super rough, like it's misfiring. It absolutely will not idle without giving it throttle and keeping it around 1500 RPM
What I've done about it:
Did a compression check, nothing unusual there.
replaced/connected vacuum lines that were rotted/disconnected
Checked timing for TDC, that appeared to be in line (as in, at TDC rotor was pointing at #1 cylinder. Couldn't get it to idle to check with timing light)
Checked for vacuum leaks with propane; didn't notice any changes anywhere along lines or intake manifold


Now what's really confusing me is this: For ****s and giggles I disconnected the brake booster vacuum line and to my disbelief it actually idled when I did this instead of dying immediately. The idle was still very rough and high (about 1500 RPM), but idled none the less.
I also disconnected the IAC (with the brake booster vacuum attached) and this also allowed me to idle without stalling at 1500 RPM.

I'm not really sure how to interpret why my blazer idled after removing the brake booster vacuum line, or if I should even make anything of it at all. Any input would be appreciated!

Meanwhile I'm going to check for silly things like spark and fuel pressure, but am at the moment slightly stumped!

 

Now that it does idle, I'd go back to the ignition first and check the timing.
Don't forget to pull the brown wire apart at the connector behind the passengers footrest carpet. Else you have the ECM messing with the advance.

 

Thanks error_401, I'll give that a whirl. My fuel pressure test was revealing- with pump on went straight to ~56psi, then dropped immediately to 50psi after the pump disengaged, and sank to 30psi after about 10-15min.

 

"Big air leak makes it idle fast" means its starving for air or way too rich. Idle solenoid?

30 psi after 10 minutes..isnt it supposed to dump the pressure at key off? I thought that was standard design for EFI systems.

 

Only on the TBI does the pressure bleed off nearly immediately.

 

I fixed it! I was reading the wrong line for the timing, adjusted the timing to where it needed to be and it runs perfectly now! I don't even care about the fuel pressure anymore, it purrs like a kitten!

 

Great you got that fixed. It sounded too much like ignition, the reason why I suggested it.