Background.
GF's 1999 Blazer 4.3, 245K miles.
Ran good, but apparently the check engine light has been on for a while
I live waaaayyy out in the hills, and don't have much for diagnostic tools.
So a strict adherence to a diagnostic flow chart isn't that helpful.

To the point, starts but stumbles and misses.
Borrowed a scan tool and checked the codes and had.

PO122 throttle position sensor, switch A low output.
PO144 Ox sensor circuit high voltage Bank 1 sensor 3. Not sure what that means since I think I only have 2 Ox sensors??
and PO3000 random multiple cylinder misfire.

1st, since I never have even looked under the hood of this vehicle I started with the basics.
Maintanance has been iffy.

So,,,,,
New plugs, rotor, cap, wires, fuel filter.
Next checked the FP pressure. 60psi while running dropped right down to 50 when the pump shut off.
Replaced pump, now 60 & 56 psi, so it is in specs.
Hosed the intake and related for vacuum leaks, none.
Checked the fuel spider, no visible leaks.
EGR pulled and checked for junk keeping it open, nothing.
Hmmm.....since I have a 1999 5.7 suburban that runs great, swapped the coil, ignition module, EGR. Not any better.
Replaced both Ox sensors, no change.

Still am baffled.
Multiple misfire mean more than one so it must be more wide based component that is the problem.
Thinking dist gear wear, cat converter fouled, ECM ??? or I dunno??

I didn't swap out the TPS with the suburban maybe I should?

Any ideas?

 

hmmmm...... nobody?

 

Read P030x Explained, and The dreaded P0300.... Plenty of info in those threads.