Idle misfire

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sean_chot

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Ram Year
2003
Engine
Hemi 5.7
So I have a 2003 1500 5.7 and I've had this problem for about the past year. When at idle, (which it barely does) the rpms will bounce around from 300-1200. It pretty much sounds like it has a race cam and is making 1200 horsepower to the wheels. It seems to be an intermittent problem but I can usually tell exactly when it is going to do it. When the truck starts, if it first revs up over 2000, it should be fine. Anything under that and it will start the misfire. It does it constantly in park and neutral. If you shift into drive or reverse it will steady out for a short period of time (maybe 20 seconds to a minute) then start misfiring. Once you get above 10 mph or so, the truck runs great. You punch it and she goes. It doesn't seem to be dependent on engine temp, but rather on the outside temp. I live in Michigan so the winters here are pretty cold. That being said, it will misfire a lot less the colder the temp outside is. It has recently started heating up the the idle has gotten worse. I have disconnected the battery, cleaned the throttle body, cleaned the MAF sensor, and checked the trans fluid. The truck has also had new spark plugs, new plug wires, new coils, new coil wire ends, new pcm, checked for broken valve springs (which none are broken) and my mechanic said that he updated the idle programming. I also just had the dealer do the fuel system flush that cleans the injectors. For the 3 days after that it idled perfectly but it's now back to what I call "the idle bounce". I've run out of ideas on what to try next and don't want to go throwing a ton of sensors in her because I don't think that will fix it. Any suggestions would help. Thanks.


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bhonshell37

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2017
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hemi 5.7
Have you considered the brand of fuel you purchase?

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sean_chot

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Hemi 5.7
Yes. I've been getting strictly speedway gas for the past year (the points are good) but just switched to see if that could be causing it. It's only been one tank and seems a little better but still has had a misfire a few times. I hope running a few more tanks through will fix it. Only time will tell


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bhonshell37

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hemi 5.7
Hmmm. Is your fuel rail pressure good?

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WilliamS

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Hemi 5.7
Out of curiosity when was the last time you did plugs and coils?
 
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sean_chot

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I assume the rail pressure is good otherwise the dealer would have told me when cleaning the injectors. It had plugs and coils about 4000-5000 miles ago


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RonJon '06

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No check engine light? One thing that comes to mind is a bad O2 sensor or circuit.
 

WilliamS

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If the idle is that bad perhaps its the idle control valve?
 
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sean_chot

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Hemi 5.7
It had a check engine light for p0300 before the injector cleaning but hasn't come back since. I also forgot to mention that it has had 2 new 02 sensors within the past year. I don't think the hemis have an IAC valve on them. And if they do, how much of a risk is there in breaking it during cleaning?


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sean_chot

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Hemi 5.7
For anyone having the same problem, I finally fixed it. Despite having and new denso bank 1 sensor 1 oxygen sensor put in, then another one swapped (same position) within a year, I decided to try a dealer sensor. $140 later, the misfire and check engine light are gone. I have heard of dodges not liking Bosch sensors but heard nothing about denso. I figured it was ok but I was wrong. If your having this issue, spend the money on a sensor from the stealer parts counter. Just keep in mind, if they have to special order it there are no returns.
 

Ramnewbie

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2017
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Hemi 5.7
I've heard this about cam sensors also, it'***** and miss with aftermarket. I don't know what is so special about stealer parts but apparently when it comes to sensors theres something to OE parts.

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Fitz-0518

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Another example of the horrible conditions in the "Parts Industry" At one time Denso was the go to supplier for quality aftermarket electronic components. No longer. More and more independent repair shops are moving to OEM dealer parts like, alternators, starters, power steering pumps. Repair techs hate to do the same job twice. My guy tells the customer, I only repair with OEM. You want budget/cheap, do it yourself.
 
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