Po172 is system rich bank 1 and po300 is multiple cylender misfire. i would get a full tuneup. sparkplugs and sparkplug wires.
SOURCE: chevy malibu 2001 code po300
P0300 is multiple cylinder misfire, meaning a engine miss is detected on more then 1 cylinder, I would have the codes scanned at auto part store to know for sure which cylinders are actually missing, if there are 2 cylinders that are missing and they are side by side, such as cyl. 1,3. Or 3,5. If so its possible u have a blown head gasket blowing in between the 2 cylinders.. 1st double check that your wires are installed correctly, the coil packs have numbers on them to assure proper location.. Note the rear head has cylinder 1 3 and 5. Some people get that confused.. Providing you have a 3.3, 3.8 or 3.1 liter engine.
SOURCE: I HAVE A 2001 CAVALIER
The P0172 code is a rich code most likely caused by the P0300. The P0300 is a random/multiple cylinder misfire code. Replace the plugs and wires.
SOURCE: my 1998 chevy astro transmission surges, but not
p0440 will not effect the way it runs. check the coil and ignition module, common on these vans, and p0300 related.
SOURCE: have a 1999 Chevy Tahoe,
* p0172 bank 1 rich. If you have access to a scan tool, I would check the fuel trim and see if engine is running rich all the time. In Chevy, if both banks are too lean or too rich, usually the cause is the Mass Air Flow sensor being dirty.
* P0420 The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, bank 1 it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter. Most likely related to the P0172 code above.
* P0300 multi misfire probable cause. Fuel injectors always seem to get the blame for this one since the there is only a lean condition to one side of the engine.
The fuel injectors on these trucks really have one problem, the poppet nozzles at the end. They can stick either open or closed. If they are stuck closed, then servicing the system will clear up the problem (I recommend that they use the 'top engine cleaner' over anything else). However, if they are stuck OPEN, then no amount of cleaning or servicing will fix the problem unless the nozzles are replaced.
Here is a TSB link to the GM's upgrade from the SCPI to MPI system for your truck. http://members.shaw.ca/betterthanyoutoo/Sticking%20Poppet.htm
Here is also a link to the conversion being done on a 4.3 V6 vortec with the same issues your having. http://www.s10forum.com/forum/f107/scpi-to-mfi-upgrade-kit-324166/
Good luck and try using fuel injector cleaner first to address the issue, Lucas fuel injector cleaner is great for the price for how much you get for it. Just follow the instructions on the bottle and you should be good for a month of injector cleaner when you fill up the gas tank.
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