Weird Idle - Pontiac G8 Forum: G8 Forums - G8Board.com
 
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post #1 of 20 (permalink) Old 07-31-2018, 12:57 PM Thread Starter
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Weird Idle

So Im a relative new owner of a pontiac G8 V6.

I rece tly replaced my alternator, battery and my purge selenoid. Now my G8 is doing this weird thing during idle. My RPMs are fanning between 550 and 700 every 4ish seconds. Its very rythmic and i cant tell if its normal or not. Whole running the cabin fan the fan speed dwindles in unison with this bump/sag in RPMs.

Im also experiencing a P0455 code. The idle iasue started before that this code popped up today and im insire if they are related.

S.O.S?
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post #2 of 20 (permalink) Old 07-31-2018, 01:19 PM
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It sounds like the purge solenoid wasn't hooked up correctly. Have you triple-checked all the connections?

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post #3 of 20 (permalink) Old 07-31-2018, 01:42 PM Thread Starter
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Nah I took it too a shop. Its pretty much plug and play is it not? Im no mechanic but it litterally just looks like it plugs right on without to much going to and from the selenoid??
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post #4 of 20 (permalink) Old 07-31-2018, 02:11 PM
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Well, you've got two problems related to a leaky solenoid and the solenoid was just fiddled with. That's a screaming coincidence. Which happened first - P0455 or the shop replacing the solenoid? My understanding of what you've written is that there were no problems you've mentioned until the shop worked on it, and now all your problems have the potential to be related to the work the shop did. I'm not saying they screwed up, but I do always start by looking at the last thing that was changed before the problem appeared.

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post #5 of 20 (permalink) Old 07-31-2018, 08:20 PM Thread Starter
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I had the purge selenoid replaced before the p0455 code was thrown. I had it replaced due to a horrid clicking noise. This particular selenoid is the one located under the hood near the intake.

Its been about a week and now the p0455 code is showing up after the repair.

Do you think the weird idle is related to this issue?
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post #6 of 20 (permalink) Old 07-31-2018, 08:21 PM Thread Starter
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And yes no issues whatsoever until the shop replaced the selenoid. Now ive got the p0455 as well as this weird idle issue.
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post #7 of 20 (permalink) Old 07-31-2018, 09:07 PM
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Depends what you mean by a horrid clicking noise.
My V6 makes a clicking and I'm going to call it a whine when I shut the car off.
These noises are perfectly normal for these 3.6L engines.
If you are not getting the clicking/whine??? then there is something wrong.
I was the same way when I got my V6 thought these sounds were abnormal when they were normal.
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post #8 of 20 (permalink) Old 07-31-2018, 09:58 PM
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Quote:
Originally Posted by BAS G8 View Post
...My V6 makes a clicking and I'm going to call it a whine when I shut the car off.These noises are perfectly normal for these 3.6L engines...
The clicking/whining sounds you hear are coming from the throttle position sensor.

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post #9 of 20 (permalink) Old 07-31-2018, 10:25 PM
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Hmm, I was told it was from the purge solenoid....
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post #10 of 20 (permalink) Old 08-01-2018, 03:42 AM
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Read similar sentiments awhile ago so set out to pinpoint the source of the noises. Narrowed it down to the front portion of the engine bay which led to the throttle body and throttle position sensor.

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post #11 of 20 (permalink) Old 08-01-2018, 06:14 AM
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I have to agree with PONY MAN when the car is cycled off that clicking noise is the throttle body position sensor resetting itself for the next start up,also at time after start up and driving for the first couple of minutes there are clicking noise from the right rear of the car thats the purge system running a self test to make sure there's pressure in the system and there are no leaks

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post #12 of 20 (permalink) Old 08-01-2018, 10:26 AM
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OP my apologies for the misinformation and thank you to PONY MAN and LTUNA03 for correcting me.
I replaced the Purge solenoid on my V6 a few years ago after the car thru a CEL and have not had a problem since.
....except, apparently with my memory of just what the mechanic told me....
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post #13 of 20 (permalink) Old 08-01-2018, 10:31 AM
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Quote:
Originally Posted by Robert Goodrich View Post

Do you think the weird idle is related to this issue?
Yes, until proven otherwise. A vacuum leak can/will cause a bad idle. Chase the purge lines around and see if there are any leaks or anything and make sure all related connectors are solid.

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post #14 of 20 (permalink) Old 08-01-2018, 08:16 PM
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Its the same issue Im having, That damn surge. I posted a thread.
You said you replaced the alternator and battery. I did the same I got same result as you. Im thinking its the alternator. I going to try put the old alternator back in and see if is the issue.

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post #15 of 20 (permalink) Old 08-01-2018, 08:17 PM
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The relearn PONYMAN mentioned ,did not work for me ,but I have a different intake setup than stock.

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post #16 of 20 (permalink) Old 08-02-2018, 11:35 AM Thread Starter
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The clicking noises were confirmed coming from the purge oid from under the hood behind and to the right of the actual engine. Since it was replaced the clicking has stopped.

The dealership diagnosed my P0455 as the EVAP vent selenoid back by the fuel tank. He wants 800 bucks to replace it. Do you all think its worth it?

As far is this weird idle thing goes wouldnt a vacuum leak severe enough to cause this not throw a code? P0455 likely wouldnt cause this idle from what i have read. Could the idle be a temporary thing relating to relearning the new alternator? (i amaware thats a dumb question lol)
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post #17 of 20 (permalink) Old 08-02-2018, 11:43 AM Thread Starter
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And just a clarifaction the clicking noise I talked about above was during operation of the car and at idle.

Here is a chain of events

Noticed clicking coming from purge selenoid confirmed it was from purge selenoid by unplugging and listening DID NOT REPLACE just hooked back up and left as is

Alternor blew a few weeks later. I replaced and confirmed its a compatable after market alternator.

Simoltaneasly replaced battery and purge selenoid

Weird idle began after these parts were replaced

Week later threw p0455 and confirmed at a chevy dealership its the EVAP vent selenoid down by the fuel tank
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post #18 of 20 (permalink) Old 08-02-2018, 12:34 PM
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Oftentimes, vacuum leaks are difficult to pinpoint and may/may not illuminate the check engine light based on severity and location. $800 to replace the solenoid above the fuel tank seems to be near the going rate at a dealership. Are there not other reputable repair facilities in the area? Under normal circumstances, engine idle stabilizes rather quickly after startup assuming all other mechanisms are functioning properly. Which brand of compatible aftermarket alternator was installed? Purge solenoid?

The clicking/whining/something moving noise I referenced above frequently occurs after the ignition is switched off. Based on the information provided by the OP, BASG8 is right since it now appears two different scenarios were being discussed concurrently.

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post #19 of 20 (permalink) Old 08-02-2018, 01:31 PM Thread Starter
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I can update later tonight with item numbers etc. With having replaced the alternator and battery couldnt the weord idle be related to the ECU tryi n to relearn proper idle speed/fiel-air mix etc etc?
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post #20 of 20 (permalink) Old 08-02-2018, 01:58 PM
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Will answer the question this way. Awhile ago, left the battery disconnected overnight to do a "hard" reset in a Hail Mary attempt to eliminate a head-unit issue. Upon reconnecting the battery, the car had an inconsistent idle for a span of five, perchance three minutes or less. Eventually, it smoothed out and started running normally. In short, something else is amiss as it shouldn't take long for the ecm to get back in touch (sync) with reality i.e. actual versus stored/preset parameters.
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