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G35 rough idle and jumpy Rpms

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Old 02-05-2017, 09:17 PM
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G35 rough idle and jumpy Rpms

I've been having some problems with my 03 g35 sedan. Just recently hit 100k. It started off slow. One day I notice the car was shaking and very rough at idle. Drove for 10 min and it didn't happen for another week. Then it did it again but went away. Now I'm to the point that it's non stop shaking idle. I will start my car at a cold start and it doesn't shake. Once the rpms drop bellow 1000 it starts to shake. When the car is completely warmed up it sits at 700 rpms but since the shaking started it fluctuates from 700 to 600 and the whole car shakes. I've taken it to firstone and they told me it was a simple fix. Told me it was going to by throttle body. They quoted me 1000 but I went ahead and bought one from Nissan and replaced it myself. This did not help at all. I did the idle air relearn procedure multiple times. I recently ordered some coil packs. Just because the car is 100k and wanted to replace them before they fail on me. The one thing that bugs me is that it runs fine when it's warming up and the rpms aren't low but once it warms up it's rough. Seems like a sensor isn't sending a signal to the engine that it needs less gas or something. It's a very rich idle. The exhaust smells strong and it rumbles from the engine. No misfire codes. I'm thinking o2 sensor maybe. Don't think it's cps sensors because the car runs fine when driving just very rich and shaky at idle. Any suggestions? I've been searching many threads for an answer and have had no luck. Will post a video of how the car sounds if wanted. Thanks in advance!
Jake
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Old 02-05-2017, 11:08 PM
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Did you scan it for codes or are you assuming there aren't any because the SES light isn't on? A lot of times a cam position sensor will start to act up and won't trip the light but will throw a code and your symptoms are common with those when they start to go bad, especially at your mileage.
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Old 02-06-2017, 12:30 AM
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Are you sure it's running rich? Sounds like you might have a vacuum leak, since it shakes and runs rough when it's warmed up and in closed loop. You said it also doesn't do it when you drive, so I would start looking at all the intake and vacuum hoses.

It could be a bad MAF, so I'd start with cleaning that, checking all connections with intake and vacuum lines. If you have a diagnostic tool I'd look at your short-term and long-term fuel trims in real-time to see how the car is really running. You can also try unplugging the MAF after the car is warmed up and seeing if the car steadies out. It will set an engine code, but that should help eliminate the MAF.
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Old 02-06-2017, 04:21 PM
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Vacuum leak is the first thing I'd look for.
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Old 02-06-2017, 06:25 PM
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Now when checking for vacuum leaks, is the best method done by inspecting all hoses first then if nothing is found continue to spray a cleaner (forgot what one) on the hoses and if the idle evens out when you spray a certain part then that's your culprit? Thanks for all the help already.
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Old 02-06-2017, 08:55 PM
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Yea, I'd double check all your hoses. You can use unlit propane, brake cleaner, and even spray.bottle with water. Not so much for it to even out, but a major change in performance. I had a bad vacuum leak and had to build a smoke machine to find it.
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Old 02-07-2017, 03:36 PM
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I tried using carb cleaner last night and I couldn't seem to locate the exact hose. I hear a hissing sound on the passenger side of the engine and I sprayed all the vacuum hoses multiple times and nothing happened. Could it be a gasket? I've read online that sometime it can be a gasket. I'll try spraying them again tonight
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Old 02-07-2017, 03:51 PM
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Quote:
Originally Posted by Jacobk4508 View Post
I've been having some problems with my 03 g35 sedan. Just recently hit 100k. It started off slow. One day I notice the car was shaking and very rough at idle. Drove for 10 min and it didn't happen for another week. Then it did it again but went away. Now I'm to the point that it's non stop shaking idle. I will start my car at a cold start and it doesn't shake. Once the rpms drop bellow 1000 it starts to shake. When the car is completely warmed up it sits at 700 rpms but since the shaking started it fluctuates from 700 to 600 and the whole car shakes. I've taken it to firstone and they told me it was a simple fix. Told me it was going to by throttle body. They quoted me 1000 but I went ahead and bought one from Nissan and replaced it myself. This did not help at all. I did the idle air relearn procedure multiple times. I recently ordered some coil packs. Just because the car is 100k and wanted to replace them before they fail on me. The one thing that bugs me is that it runs fine when it's warming up and the rpms aren't low but once it warms up it's rough. Seems like a sensor isn't sending a signal to the engine that it needs less gas or something. It's a very rich idle. The exhaust smells strong and it rumbles from the engine. No misfire codes. I'm thinking o2 sensor maybe. Don't think it's cps sensors because the car runs fine when driving just very rich and shaky at idle. Any suggestions? I've been searching many threads for an answer and have had no luck. Will post a video of how the car sounds if wanted. Thanks in advance!
Jake
With a fourteen year old vehicle you can keep guessing, replacing various parts that are not the root cause, and wasting time and money.

OR

You can spend the one hour diagnostic fee at your local Infiniti dealer by a trained tech using the Consult lll to tell you what the problem is.

OR

Just carry a screwdriver with you so when it finally dies just take off the plates.

Just my $.02

Telcoman
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Old 02-11-2017, 11:56 AM
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Turned out to be something as simple as the valve covers leaking. I had replaced them this last summer and now they are leaking again. The engine was 2/3 of a quart low on oil. Gonna cost me 1800 to do it with the dealership and then I'm saving and getting rid of this g
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Old 02-11-2017, 12:13 PM
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How come you don't do it yourself? It's not too terrible as long as you keep track of everything you take off. If not get a local trusted mechanic to do it. It's about 3 hours labor time. Get parts from rock auto (they sell both the gaskets and covers if you need both) and you'll be golden and save a ton of money.

Last edited by victor0206; 02-11-2017 at 12:14 PM. Reason: Mispelling
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