I have an 06 300C heritage with 74,000 miles. It has a problem I am determined to solve.
The symptoms: On cold start up: sometimes runs rough like it's missing a cylinder. If I turn it off and restart it it runs rough for a few seconds then smooths out and runs good. Sometimes it cold starts normal and runs good but when the oil temperature reaches about 70 degrees it runs rough but smooths out by the time the oil temp reaches 80 degrees. Also, in third gear around 2000 to 2500 rpm while accelerating lightly the RPMs will drop 200-300 RPM suddenly like a hesitation then it resumes accelerating. It does this in auto and manual mode. So far it has thrown codes P0301 and P0300.
What I've done so far: Replaced spark plugs with copper tops, EGR valve, MAP sensor, ignition coil and cleaned the throttle body.
When it showed code P0301 I swapped cylinders 1 and 3 coils. After that it showed P0300. Thinking the coil I put on cylinder 3 was bad I replaced it. All the symptoms remained. This morning it showed code P0301 again. Before I left work I swapped 1 and 3 coils again putting the new coil on cylinder 1. After that I got a good smooth cold start up but the hesitation in third gear stayed but not as bad.
Next I'm gonna get a mechanics stethoscope to listen to the fuel injectors and valves and wait to see what codes it shows next.
I had two cold start ups today and no misfires. It does still hesitate in third gear though. This is happened before and it will probably start misfiring again in a couple of days. Tomorrow I'm gonna get a stethoscope and a multimeter out and check out the injectors. Does anyone know what the resistance is suppose to be for these injectors?
Yesterday the cold start misfire came back with a vengence. This time it didn't smooth out when I restarted it. Also, I heard a click three times and it would stumble like it was going to stall for a few seconds after it did it. I kinda sounded like the throttle body slaming shut.
Today I measured the resistance of the injectors and they were all close. I put the stethoscope to them and they were all clicking the same. I also listened to the valves and didn't hear anything I would consider abnormal.
I also looked at the EVAP system. The only thing I could find was where the EVAP purge solenoid outlet hose has been rubbing on a wiring harness on the right rear of the engine but it didn't look like had rubbed through.
Next I am going to look at TPS and throttle body because of the clicks that I heard. And because the condition is worst when cold I am going to look at the IAT sensor.
I just tested my IAT sensor. I don't know what the ohm resistance range is suppose to be but the resistance dropped as I heated the sensor with a hair dryer. It responded quickly so I guess I can assume that it is ok. I'm gonna keep looking for a way to test the throttle body. The cheapest one I've been able to find is $220 so I want to make sure that is it before I spend the money.
Still having the same issues. This weekend I changed my oil and switched to Mobile 1 5w20 and a Mobile 1 filter. I also did a dry compression test. First off, the oil didn't solve my problem but it made a big difference on how my engine runs. Its smoother, quieter and seems to rev quicker. The compression test showed 150 to 160 psi on all cylinders and they all built pressure the same. I know this shows the pistons, rings and valve seats are good but, is it safe to rule out a broken valve spring? I ordered a DiabloSport intune, so my next plan is to turn off the MDS, then try a canned tune to see if it makes a difference. BTW, after the compression test it threw P0301 and P0113. I checked the IAT sensor then cleared the codes. They haven't come back. Yet.
Keep us updated... I am following along... your just doing things as I would to be fair so not much to say! Lol... you could look into a cam position sensor and a crank sensor.. they can cause a whole host of weird little gremlins!
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Single cylinder misfires usually aren't problems that would affect all cylinders like a sensor, so I would concentrate on that cylinder. Perhaps a coil or injector wire or connector, did you do a good wiggle test of the harness?
Beer for my men....and NOS for my horses.
Hello, so I'm not sure how this all works as I am new to this but I like the fact of getting advice from ppl who know what they are talking about. My 300 is not as fancy as most of you all however I have gotten codes P0300 P0301 and P0303 I know they are misfires but the car is shaking once it has warmed up and when I stop at a red light it shakes not extremly bad but i can feel it. I don't want to have to pay seriously crazy money to get it fixed can anyone please suggest what may be wrong with my car please. thanks in advance.
You might need spark plugs. Usually when you post a question you would start off your own thread, you kind of highjacket this persons thread by posting your question here. So to keep everything from getting confusing as to who and what vehicle we are talking about you would have your own thread.
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