I am hoping someone can help pin down my problem. I have read many of the posts about the dreaded 0300 code, and there are lots of possible causes. My blazer is a 1995 4.3, CPI, OBDII, 165K miles. It started idling real rough and stalling when cold. Tach would jump up and down, and it would be hesitating when accellerating. Once the truck gets up to normal temp everything smoothes out. I got my hands on a Tech II, and the only code it is generating is the P0300. No other trouble codes. I took some readings without the code and with the code. The first reading is without. I only listed the sensors where something changed:
ECT Sensor 1.88V, 1.02V
MAP 1.43V, hopping between 2 and 3V
MAP 37kPa, hopping 39-60kPa
HO2S Bank 1 Sensor 1 525mV, hopping 600-800mV (Is this in front of the cat?)
ST FT 14%, -40 to -50%
KS Activity 0, 212.
Engine is obviously stuck on RICH when coded, so that might explain the different values.
I get no codes on the EGR or anything else. Fuel to air is 14.7:1 like it should be.
A friend thinks on of the pop-it valves on the end of the spider is sticking. He suggests I replace the spider. Is there a replacement brand recommended? ( I have seen online that some come with individual injectors).
Truck has only had 15K miles put on it since 06- it's had a new fuel regulator, fuel filter and tune up. The shop where I take it is stumped.
The question that might be the clue to the whole problem is why does it run normal when warm?
Can anyone offer any suggestions?
Thanks in advance for any help- the truck's been in the family since new, so I don't want to give up on it.

 

So- a friend helped me change out the CPI (spider) and nut kit. We also replaced the EGR valve gasket with one that has a screen in it. Truck is running MUCH better and not throwing codes. Every once in a while it has a slight roughness to idle, but evens back out. Got 19.6 mpg after the change- best mileage I've had in years!
I recommend the Chilton repair manual- it had great instructions, pics and specs.

 

Sounds like you need a tune up. Cap,rotor, plugs and wires. Be sure to use delco parts or you will probably keep getting random misfires. You may also unplug the maf, drive it and see if it helps. If it does then its just a simple cleaning required.