Rough Idle - ways to tell what _might_ be cause?? - Pontiac G6 Forum
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post #1 of 10 (permalink) Old 08-03-2018, 12:36 PM Thread Starter
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Rough Idle - ways to tell what _might_ be cause??

Hi, 2010. I have been noticing a bit of rough idle lately. I have had the car for 2 plus months. Either I did not notice before or it has just started. It does not seem to be that rough, but, I really do not have the 'education' to know for sure.
I have only really noticed when stopped for a light [I am writing this before just sitting in the parking lot - though any time I needed to do stuff after starting and shifting I have not noticed anything but those times were short.] The pickup and power seem okay. Much better than my old car.

If I were to start the car and wait, should I rev it up and look at the tachometer? If so what am I looking for?
Would vacuum leak act differently than spark plugs or ignition coil, etc? I only know to ask about these after a Google search that said: 34% chance of Vacuum leak, 21% spark plugs and 15% coil for causes.

Would the mechanic who looked at it before I bought it have seen anything? He was recommended by the car dealer.

I have read that if it is a vacuum leak I should do something _soon_!

Thanks.
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post #2 of 10 (permalink) Old 08-03-2018, 02:40 PM Thread Starter
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I just went out to the parking lot. The car has been sitting overnight. Started it up, it went to 1.5 K rpm and slowly dropped to about .9K rpm and was less than totally smooth but not as rough as before. I ran it up to 2K and it settled down to .9K again. I did not run it for more than a minute but it seemed as though it would stay at .9K, whereas when it first dropped I was afraid it would sputter off.
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post #3 of 10 (permalink) Old 08-03-2018, 02:51 PM
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To check for vacuum leak, get some flammable carb cleaner or brake cleaner, or propane works to. Start spraying it around all gaskets and hoses. When the idle revs a little, you found your leak. Alternatively you can use a hose with the water running at a trickle. Same procedure but listen for a drop in idle. As far as checking the coils, you really need a oscilloscope and the ability to know what to look for. Spark plugs usually last 100k. If they are not A/C Delco or Autolite, they might cause a small hesitation under load. Use German Plugs for German Cars, American, Japanese... you get the picture. The wires I would guess are usually a problem on GM V6 engines. They rest on top of the motor, getting hot and vibrating. Anywhere they touch anything including another wire, look for a black spot. Arcing. When the spark jumps out the worn insulation causing a miss. Could be a intake manifold gasket going out as well, these engines are notorious for that. You get fouled plugs. Hope these tips help.
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post #4 of 10 (permalink) Old 08-04-2018, 08:54 AM Thread Starter
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Thank you for the tip and the quick replay!
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post #5 of 10 (permalink) Old 08-05-2018, 12:40 PM
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Dosent say the year or size of engine, my 2008 v-6 has a rough idle but runs great. It has new AC Delco iridium plugs and wires.
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post #6 of 10 (permalink) Old 08-06-2018, 07:32 AM Thread Starter
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First line: "2010".
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post #7 of 10 (permalink) Old 08-07-2018, 12:32 AM
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There are so many things that can cause a rough idle. I could print 2 pages of possible causes. Start by doing this, hook up a fuel pressure gauge and put it under your wiper blade so you can see it from inside the car. Hook up a old timing light to a ignition wire and tie strap the light to stay on. place it in the car so you can watch it flash. Now drive your car and pay attention to both and see which one sputters when it runs crappy. You may have to run the timing light to each of the six wires one at a time till you find it. Most performance problems are fuel or spark related. This will help to A. Determine which one it is and B. if its spark related possibly help you find which cylinder.
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post #8 of 10 (permalink) Old 08-08-2018, 01:46 PM Thread Starter
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Sounds great _if_ I had any of that. I don't even have a garage, much less tools to keep in one. 8-)
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post #9 of 10 (permalink) Old 08-11-2018, 12:54 PM
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Well then see if a friend can help or its off to the shop.
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post #10 of 10 (permalink) Old 08-28-2018, 09:47 AM Thread Starter
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Took it to the shop. $100 plus for inspection and diagnostic. One bad spark plug and its wire and a bunch of codes. They cleared the codes and replaced the _original to 2010_ spark plugs and all the wires.

After a test ride they said the codes did not come back.

For the future: oily touch to sides of engine below the valve gasket - not bad enough to worry about for a year or so. Minor leak in back shock also able to wait, they say.

Inspection, diagnostic, 6 plugs and 6 wires = $485.
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