Causes of a P0300 code in a 2003 ford ranger?

Answer 1

Trouble code P0300 means: Random Misfire Detected After getting this code, along with a P0171 and PO174, I did a little research. Yes, this code does mean that a random misfire was detected, but the cause isn't specified.

Someone on another site suggested checking the vacuum hoses for a collapsed hose or a split. After looking extensively, and listening for the hiss of a leak, I found just exactly this problem. Most of the vacuum lines under my hood are plastic, but up under the throttle area, there is a right-angle rubber hose that attaches to a long approximately 5/8" dia plastic vacuum line, then turns and connects directly under the throttle area. This hose was "clamshelled" - collapsed - and had a nearly 1.5" split in it. I went to our local auto parts store, and while they didn't have a vacuum hose replacement part, a small diameter cord-reinforced rubber hose fit perfectly. Replaced it, cleared the codes, and haven't had a problem since.

Hope this helps.

Answer 2

P0300 Diagnostic Code - Random Misfire

Symptoms.
Engine may stumble or miss
Engine may be hard to start
you may notice no issues

Cause
Failing spark plugs or spark plug wires
Bad coil or coil pack
Failing oxygen sensor(s)
Bad fuel injector or more than one
Stuck exhaust valve
Bad catalytic converter
EGR valve or valve passage clogging
Bad camshaft position sensor
Bad PCM or ECM

The Fix
Best first action is a tune up, new plugs, wires, inspect all hoses and wire connections then reset the code. If it returns you will need to narrow it down to a system, coils and coil packs should be tested, catalytic converters for function ( do you smell rotten eggs?). A misfire that jumps cylinders could indicate a lean condition, do you have any other codes along with the 300? this will help clue you in to the source, check valve function to make sure they are opening and closing fully.
This is probably pone of the most difficult codes to troubleshoot, so start with the basics and work your way into the more expensive options, in many cases a good old tune up solves the problem, back it up with a fuel system cleaning and see where you stand.