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Discussion Starter #1
hello. just bought a 300c 2005 a month ago and when the engine is at its normal temperature its idling at 500-550! (idk its normal or low) ....its giving some sort of vibration or shaking...this shaking fluctuates from minimum to some maximum on idle (by fluctuate i mean at some starts its minimum vibration and sometimes its maximum*mostly at cold start)....but if i shift the gear to N (neutral) the RPM jumps to around 600-650 and the shaking is reduced significantly....there is no vibration on driving but i feel that the drive is not as smooth as it was before....it feels like the car is hard
things already done
1) Changed spark plugs (CHAMPION SPRE14MCC4)
2) Poured Ac delco fuel injector cleaner in full tank (60 liters)
3) Throttle body Cleaned
4) new air filter
5) Changed Oil (5w-40 castrol edge fully synthetic)
6) Got the factory setting map uploaded.
* using a 98 octane fuel.
 

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Did you check the gap on your spark plugs? You can try to replace the cam position and crank position sensors. Both very cheap and very easy to replace.

Is there any reason you're running 98 octane? Have you tried running a couple tanks of 91 to see what happens?
 

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Discussion Starter #3
No i didnt checked the spark plugs gap (does that create a big difference).....i don't want to just buy parts and keep on installing i asked a mech and he told me to replace the plug wires (coils) and check if that works but i don't want to try this try that method....i just read on some threads that PCV valve is easier to be removed and replaced or cleaned.....so was thinking to get it done.....basically v don't have 91 octane here in Kuwait. its 93,95 and 98.and its really cheap...so i go for the best one...
 

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Well I would pull the plugs and check all the gaps before I go replacing coils. Also, if it was your PCV I would think you would have other symptoms BUT if you wanted to replace it just to see if that's the problem just consider it preventive maintenance since they are notorious for having issues and it then you won't have to worry about that for a longtime.

As far as the gas goes... 98 wont hurt it but unless your car is tuned for it you won't gain anything from it. I would try a few tanks of 93 from a different gas station and see if that makes any difference. Could be bad gas too.......
 

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Discussion Starter #5
So u suggest nt to take tht pcv out ........wht shd b the gap for the plugs....I ll get it done today....and is there any site or something from where I can get the 98 octane map ? Any idea at wht octane is the 5.7 hemi tuned by factory ?

Sent from AutoGuide.com Free App
 

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To be honest I'm not sure that the stock tune is written for on the C. I assume is is 87 but again I'm not sure. If you want to tune for higher octane you should go to the diablosport website or find a used predator, intune or trinity on here. That will allow you to tune for 93 but you could get a custom tune written from Johan or anyone else for that matter for your 98.

My warm idle is going to be different because I have a custom tune and a cam. I can't recall the stock warm idle but I'm sure someone will jump in here and tell us.
 

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Discussion Starter #8
mmm....so u must b arnd 300whp.....thts cool
i m thinking of getting the basic done today....like getting the fuel filter clean,spark plugs adjustment etc
btw whts the spark plugs gap..... .053 ?
 

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I haven't been on a dyno but I expect the car to be around the 415-420HP range. Friend of mine, same car, same mods, same cam, gained 40HP just from installing that HHP stage 1 cam.

I don't remember the gap for our cars but if you search for it I'm sure it's on the web somewhere or even in your manual. If I were you I would start by putting OEM spark plugs in with correct gap and replacing the PCV. If you want you can replace the cam and crank position sensors too as they are cheap and easy.
 

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What's with the 5W40 oil when the OEM requirement is (at least here in the U.S.) 5W20?
 

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Discussion Starter #17
Well i just noticed something......while on stop i press the RPM to around 1.5-2 and its like droping with constant foot on Accelerator and the light in the CLOCK blinks slightly.......so my question is that IS THE MISSING OR SHAKING IN THE CAR DUE TO LESS POWER SUPPLY OR SOMETHING....?
i changed my car battery a month back and its still new......
 

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Discussion Starter #19
Did you solve problem with vibration at idle??
I have the same too.
Ricky get ur car flushed n put some good oil in it and change air filter n plugs plus if u can then get ur throttle body n injectors cleaned......u ll have a much smoother ride.......
 

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My hemi has only 53,000 km, I have little vibration after 4 years from bought.
I tried clean throttle, change plugs, filter, injectors and...nothing has changed.
Maybe some PCM update can solve problem.
 
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