Idle surging only with AC off
11-21-2012, 12:22 PM
#1
Staging Lane
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Idle surging only with AC off Sorry if I missed the answer to this somewhere, but I wasn't able to find it. As the title states, my car (98 SS) jumps between 1000-1500 rpms when at idle with the AC off. I've pulled the IAC and cleaned it and verified its operation. I do have a SES light and the code P0507 stating IAC issue (higher rpm than expected). I've double checked the vacuum lines and I don't see/hear any leaks. I've unplugged the IAC as suggested somewhere else and no change to idle. If I squeeze the PCV return to the TB the surge goes away. Do you guys thing maybe the PCV valve is faulty? I'm running out of ideas. Thanks.
11-21-2012, 12:39 PM
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It is either a hidden vacuum leak or stuck open pcv valve or a lean mixture. Blow air on both sides of the pcv valve, it should allow air on one side. To check for leaks, spray carb cleaner around the intake and injector o-rings.
11-21-2012, 03:33 PM
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So I tested the PCV valve and it operates as expected. Only allowing air into the TB. I also sprayed everything with carb cleaner and no signs of a vacuum leak. So additional info, today it surged whether a/c was on or not. Also it seems very slow to come to idle. Basically stuck at 1.5-2k until I have come to a complete stop and about 5-10 seconds later it will fall. Thanks guys.
-Dustin
-Dustin
11-21-2012, 06:44 PM
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Thanks for the responses. So far I have replaced the canister purge solenoid and capped the passengers side pcv on the rear portion of the valve cover since I was there anyways. I tried disconnecting the maf and there was no change.
As far as a tune. I had a base tune about 2 years ago to account for my bolt-on mods. I still find it weird is that if I pinch the pcv return to the TB the surge stops until I give it gas. I bought another pcv thinking that my aftermarket pcv might be casing some issue because of internal spring tension, but I need to buy the hose adapter. This issue seemed to start suddenly when it would surge too low and die. I found some vacuum leaks and a bad pcv. I change all that out and things cleared up for about a week.
As far as a tune. I had a base tune about 2 years ago to account for my bolt-on mods. I still find it weird is that if I pinch the pcv return to the TB the surge stops until I give it gas. I bought another pcv thinking that my aftermarket pcv might be casing some issue because of internal spring tension, but I need to buy the hose adapter. This issue seemed to start suddenly when it would surge too low and die. I found some vacuum leaks and a bad pcv. I change all that out and things cleared up for about a week.
11-26-2012, 10:48 AM
#7
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So after creating a makeshift adapter for the stock PCV and installing it everything seems to be back to normal. I noticed that the stock PCV allows a little bit of back flow under low pressure. I'm assuming this is why the aftermarket one I used didn't work correctly. Luckily I decided to check the gas tank to see if there were any leaks back there, because I found that all of the nuts that hold the pump assembly in place on the top of the gas tank were loose. I don't think this helped anything but at least my pump wont makes its way out.
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10-03-2013, 06:38 PM
#8
Mines also a 98 ls1 but the only difference is i installed a ls6 intake and ls6 valley cover on it. So i dont have the stock pcv system anymore.
If my car has never been tuned, can the stock tune still be a little off?
Also, i noticed that if i have the car in idle with the ac off, and i remove the rubber elbow right before the throttlebody, (along with maf sensor and lid,) the car seems like its gonna die completely, so i have to reinstall the elbow to make the idle climb back up.
Car is a m6 98 ws6 with stock internals and few bolt ons. Only codes are p0405 and p0410 both which popped up after doing egr and air delete.
Any ideas on what to check?
10-06-2013, 04:36 AM
#10
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Sounds like a vacuum leak to me. I would keep looking for the leak. Taking the maf and elbow out of the intake system is letting un measured air into the system cause it is not passing through the maf (making the car run lean). I would not do that anymore. The reason you dont have a problem with the vacuum leak with the ac on is because the car bumps the idle rpm up when ac is on to compensate for the extra load. Honestly, if I could not find the vacuum leak in a hose or by spraying cleaner, I would start replacing gaskets and seals until I fixed it. The ls6 intake is supposed to be installed to like 83 inch pounds too I believe. Easy to over torque those bolts. Maybe that is where your leak is from. My .02 cents...
10-10-2013, 08:41 PM
#11
Sounds like a vacuum leak to me. I would keep looking for the leak. Taking the maf and elbow out of the intake system is letting un measured air into the system cause it is not passing through the maf (making the car run lean). I would not do that anymore. The reason you dont have a problem with the vacuum leak with the ac on is because the car bumps the idle rpm up when ac is on to compensate for the extra load. Honestly, if I could not find the vacuum leak in a hose or by spraying cleaner, I would start replacing gaskets and seals until I fixed it. The ls6 intake is supposed to be installed to like 83 inch pounds too I believe. Easy to over torque those bolts. Maybe that is where your leak is from. My .02 cents...
10-10-2013, 09:05 PM
#12
i also notice there was a small leak of gasoline from the gas cap after filling her up. Im not sure if its related or i forgot to seal the gas cap correctly.
Any help would be appreciated.
Any help would be appreciated.
10-10-2013, 10:02 PM
#13
heres another thing, i unplugged the iac and turned the car on. It sounded a bit deeper and after the cold idle, it jumped up to about 2k rpms. So i turned it off and plugged the iac back on. Does that mean the IAC works properly?
10-11-2013, 02:51 AM
#14
Like mentioned earlier it's most likely in the tune. My 98 is the same way but I'm a new tuner so I'm still messing with it. It's something with the IAC. It's not faulty but you can control the speed at which it closes and opens. Most tuners dont fool with it but sometimes you have to and from what I'm told it's more common on the 97/98 models or if you swap to bigger TB's you have to fool with it.
10-11-2013, 03:43 PM
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Have You looked through the "diagnostics & tuning" forum in LS1 Tech ? Also You might try websites like Aitn ,,,,,They are a mechanics website that basically deals with everything to do with engine diagnostics & tuning They list all the possible codes and everyones repair for each particular code.
10-11-2013, 03:59 PM
#17
Have You looked through the "diagnostics & tuning" forum in LS1 Tech ? Also You might try websites like Aitn ,,,,,They are a mechanics website that basically deals with everything to do with engine diagnostics & tuning They list all the possible codes and everyones repair for each particular code.
10-22-2013, 02:57 PM
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As far as it possibly being in the tune ,,,,,,yes absolutely ,,,,,,,,,,that's why there are so many reflash updates ,,,,,,to address issues like that ,,,,,,,that does'nt mean it is for sure that ,,,,,,,,that's just 1 of the possibilities . BTW , that other website I mentioned is iAtn not aitn, sorry and good luck