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Discussion Starter #1
anyone have this problem?.. misfired one time and almost died, got a p0300 .. cleared it with my obd..so i changed plugs, new egr, and threw a bottle of chevron fuel system cleaner.. i notice when i hold the throttle at about 1800 rpm it still feels like it has a slight misfires, but runs fine when you just drive normal threw the gears and idles fine .. and does not throw a code though.. is it because it does it misfire enough to throw a code? trucks run fine unless you really look for the misfire and try to old 1800 rpm.. anyone ever had this issue?
 

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Can you attain higher rpms like when passing. I have a 5.2l that I could not get over 3400 rpms and it ended up being a bad cat. If this is your problem a quick check is remove and tie back the precat o2 sensor and try it again. A little noisy but it allows less back pressure to see if you got a plugged cat.
 

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Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.

A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

Symptoms
Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present
Causes
A code P0300 may mean that one or more of the following has happened:

Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer
Possible Solutions
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
 

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Discussion Starter #4
ok well it did it again stumbled at about 1800rpm felt like it was gonna die, sounds like its back firing and misfiring, the engine light started blinking .. pulled over and then the idle smoothed out and engine light went off.. and drove normal the rest of the day.. i do notice it only does it when the engine is cold like first start of the day.. when its warm it doesnt do it.... i put new plugs, egr, pcv, and injector cleaner about 2 weekago... checked the code it was p0300 again.. lost dont know if i should take it to dealer to look at.. anyone ever had this problem?..
 

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Try to take it above 3000 rpm. If it fails to do this, remove your precat sensor and tie it back out of the way and go for a drive. Yes it will be noisy but if your problem does not continue you have a bad cat that is giving too much back pressure. Removing the o2 sensor releives the back pressure for testing purposes.
 

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Discussion Starter #6
the truck has no problem going over 3000rpm ... in fact when you get on it, it drives better no stumbling.. it only happens on very lite throttle..especially when you try to keep it about 1600 to 1800 rpm..
 

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need to use a more advanced scanner to see the exact P0300 code...also, what spark plugs are you using?
 

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Discussion Starter #10
oh really good to hear... was gonna take it to dealer for a scan but maybe ill try that sensor first.. were is that sensor located? ... and is that a dealer part only?.. thanks
 

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Discussion Starter #13
2 new upstream o2 sensors.. seems like problem is gone... but need to drive more to make sure.. thanks for the help guys..
 

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id check and see if you can locate which cylinder is misfiring and switch over the coil pack to another cylinder and if it changes your misfiring cylinder to the one you switched it to it's probably a dead coil pack i just diagnosed this problem on a 2005 envoy and this is a simple test that doesn't take long or alot of effort to see and could possibly save you some time and money in the long run.
 

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I'm having the same exact problem right now.I've elimated the plugs and wires.I'm fairly certain it's not a valve problem.I don't smell rotten eggs so I feel pretty good about the cat conv. too.I'm feeling like its a half shot sensor but which one I don't know.
 

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I am having this problem as well! I am going to look at the sensors at rockauto and try to replace them myself I think. Probably changing all of them just to be sure.
 

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I've got a 05 Hemi in my truck and had a small miss, replaced all spark plugs and drove a little better, a couple days later pulling out of my drive way it started missing terrible, popping under the hood and extreme loss of power, check engine light came on with the P0300 code, replaced all the plug wires and ran great for a few days, leaving my house again and same sanareio, popping and loss of power, but I noticed that if I shut the truck off and start it back, it runs fine again for a few days. Any ideas?
 
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