When You step on the gas in my 96 Cherokee sometimes it hesitates if I take my foot off and reaply gas it's ok then I get code P0300?

Answer 1

The very first thing that I would try, and the least expensive would be to clean the throttle body.

Take the plastic lid off the top of the engine (find it by going from the big air filter box via the large plastic tube that goes to the top of your engine). Underneath that you will see what looks to be a carburetor but what is in fact the opening of the throttle body. It has a flat piece of metal that opens and closes automatically due to instructions from the engine and all the black boxes. If you fiddle around with all that when the engine is not running you will find the linkage that would move and provide more gas if you foot was on the gas petal. This is not too difficult.

What you need to get is a can of throttle body cleaner from your local parts store. Not carburetor cleaner but throttle body cleaner. Spray a couple two second sprays into the top and then try to start the engine. It may take a turn or two to start because the stuff you sprayed in there actually will burn and will act as if you have flooded the engine with excess gas. If the engine starts let it run for a minute and then turn it off and spray a bit more in there. What you are doing is using that solvent to remove the build up of tars and other junk that makes the whole system stick and not work correctly. If you have a friend there you can have him/her start the engine and you can stand by and spray very small amounts of that cleaner in while they rev the engine. You will find that if you don't rev the engine it will probably stop. This is normal and just means that you have put too much flammable stuff into the fuel system. ]

If the problem is just a matter of dirt and gunky build up in the fuel system this cleaner will absolutely take care of the issue and potentially save you a ton of cash from the repair place.....who would do this first anyway.

If using this cleaner stuff doesnt take care of the problem then I would suggest taking it to that same repair guy and hope for the best. I've taken care of starting and running issues several times with a 4 dollar bottle of cleaner so I feel that this is a good first start. Please make sure that if the engine is running that you stay well clear of the belt and radiator fan on the front of the engine.....death and destruction may result if you don't.

ALSO - the code that you're getting may go away if the throttle body is clean but it may also stay there. If you still get an error code and the engine is running right you will need to have the black box cleared with a test set. I recommend going to one of the major auto parts stores (preferably where you bought the throttle body cleaner) and having them put, normally at no charge, the computer reader which will clear that error code from the vehicle. What a pain right?

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.