I've got a stock 156,000 mile 87 LB9/700R4 IROC. Its pretty much all original, except for a few maintenance items such as alternator, radiator, water pump. When I go to replacing parts, I always go with AC/Delco since I get a good deal at local dealership. About two weeks ago, my IROC started this hesitation right off idle, such as accellerating from a stop light. It got worse and now you can feel it hesitate while reving in Park/Neutral. It revs slow compared to before. Now any time you try to accellerate, it will stumble and will eventually stop running if I don't let off the throttle. It even sometimes backfires.

Now my dealing with backfiring TPI's resulted in a MAF change. So that was the first thing I tried, which didn't help. Well, here's a list of all that I have checked:

MAF is 5 gm/sec @ idle > over 130 at WOT
TPS is .54 @ idle > 4.37 at WOT (was no dead spots)
Throttle body has been removed/cleaned thoroughy
IAC has been clean and reset
Replaced Cap and rotor
Swapped in a new coil (but put old one back on cuz it didn't help)
Fuel filter changed
Checked backpressure on exhaust ( less than 1 psi @ idle > 1.5 psi at 2000 RPM which was well within spec according to my GM manual)
Ignition module was checked twice both hot and cold
Checked and replaced a bunch of vacuum hoses/lines throughout engine
Used two different PROM chips
Base timing at 6*
Removed vacuum source from EGR temporarly just to check
02 is reading lean 90%
Block learn is 148-153
Knock retard will occasionally pull 1 or 2* during the stutter until I let off throttle
Base idle in P/N is a steady 700 RPM's
Sparkplugs (R43TS AC/Delco) gaped to .035 and plug wires checked with DIS/kV tester (all was around 10 kV @ idle)

My main question, other than that I'm at my wits end trying to diagnosis this problem, is what is the minimum fuel pressure needed to supply a TPI until you experience problems. When KonEoff, Pressure goes to 25 psi or so the first time, 35 or so the second time. With engine idling, pressure is 32 psi and drops down to about 25-27 psi while reving it through the stutter up to 3500 RPM's. I know my pump is 16 yrs old, and is in dire need of replacement. I already have a brand new AC/Delco fuel pump ready to go in, but I want to know for a fact that this is where my problem lays before I go through cutting my exhaust off. I've checked everything my GM service manual mentions for the hesitation/stumble symptom except the canister purge system and injector balance test. This manual says 32-47 psi is idle range. Doesn't give a spec for reving or even a minimal.

I really need some help here guys. I'm about out of ideas, and the ECM is not helping me either. It's not threw a code the first time throughout my testing but had a code 36 about a month before all this happened, but its not showing up now (I have a new MAF Burnoff Relay ready to go in). Any help will be greatly appreciated and welcomed.

Thanks in advance.

 

Installed new MAF Burnoff Relay (AC/Delco) today, but as I figured, it didn't help the least bit.

I'm totally lost on this.

 

I can't remember exactlly, but here is what I am thinking. I know that the 305s ran 39.5psi for the early years, what I can't remember is if they were bumped up to 43.5psi for the later years.

You need to at least make sure that you hace 39.5, and then by the time you check it, maybe someone else can chime in.