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Not idling correctly after replacing vapor purge valve

Tiny
WPATTERS1229
  • MEMBER
  • 2005 CHEVROLET EXPRESS
  • 6.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 146,000 MILES
I replace the vapor purge valve with a standard part #CP470, but it did not come with a rubber gasket that was on the old one I took off the engine. I reused the old gasket but it did not lay flat since the new part had a light grey plastic piece but it was fixed to the part. After replacement, the engine would not start at a fast idle or idle the correct speed. It idles around 550 rpm. No codes came up on the OBD2 scanner. Should it have been installed without the rubber old gasket?
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Wednesday, May 27th, 2020 AT 10:18 AM

15 Replies

Tiny
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I put in the old valve. Nothing changed. But I also installed two new O2 downstream sensors. The fuel trims and the voltage of the O2 sensor look good. My problem is that the idle will not go much past 600 rpm. It barely starts but also does not stall. I have disconnected the battery to reset the PCM to see if that is the cause. Have not done a drive cycle to see if the not ready items change.
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Wednesday, May 27th, 2020 AT 5:59 PM
Tiny
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Is the idle smooth and steady at 600 RPM or is it rough? Is it just lower then it was or is there another issue? What did it use to idle at?

I attached the info and testing on the Idle Air Control which is what controls the idle speed.

I attached the process for the purge solenoid and I don't see a gasket that needs to be installed so it is possible that was the issue.

Clearly it seems like there could be more air entering the engine but normally when that happens it raises the idle or makes it unstable. So let us know this info and we can go from there. Thanks
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Thursday, May 28th, 2020 AT 5:27 PM
Tiny
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Thanks for the reply. I put the old purge valve back and then ran it again. Not much difference. The voltages going to the downstream O2 sensors did not look very good. Since I had replaced the upstream sensors about 6 months ago I decided to replace the downstream ones. I then disconnected the battery for a couple of hours. Today it seemed to start with a fast idle and then ran down to around 500 rpm's. After it went into a closed circuit the O2 voltages seemed to be more in line. I took it out for a drive cycle and the only two ready parameters that did not go okay. Are the catalytic converter and the VAP. Here in CA the VAP is not necessary but I need to get the catalytic converter to go Oklahoma. I am thinking it will just take a while to get that one from what I have read.
The other emissions items seem okay. This engine the PVC is not repairable as it is automatic. So the manual says. The EGR is not throwing a code. In fact no codes at all.
The thing that drives me nuts is the fact that the idle is low. It should be around 700 - 900 rpm. No low idle codes or misfires etc. I guess I just need to drive it and get it hot enough to get the catalytic converter's to pass.
If you know of any trick to do that let me know.
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Thursday, May 28th, 2020 AT 7:53 PM
Tiny
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I attached the drive cycle that you need to follow in order to force the catalyst monitor to run. It is not the easiest to get to run so just read through the whole thing and then drive to an area that you can perform the entire thing before trying to start it.
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Friday, May 29th, 2020 AT 7:08 PM
Tiny
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I have read that you can also get the catalytic converter to go ready by running the car after it is warmed up for 3 minutes at 3,000 rpm's. A smog tester said to drive the car at 55 mph to 60 mph for 30 miles. It seems like it is just a case of running the vehicle for a while at a certain rpm to get the catalytic converters to heat up.
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Friday, May 29th, 2020 AT 11:35 PM
Tiny
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Yeah that is a common misconception. It is possible for the monitor to run by doing these things but it is because it saw the steps laid out in previous drive cycles and it finally passed the monitor. However, if you follow the steps it will pass quicker if there are no issues causing a DTC. Doing the things you mentioned has caused a lot of people a lot of frustration because they do them and it doesn't pass. Again, it is worth a try but if it doesn't work, the steps will need to be done to get it to pass. Otherwise, you can just drive the vehicle as normal and it will pass eventually. This process exists for those that have to pass emissions testing and the need to run and can't wait for it to just happen on its own.
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Saturday, May 30th, 2020 AT 4:06 PM
Tiny
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Everything has passed but the catalytic converter. I ran a process that supposes to fix that. It says warm up the engine. Then run the vehicle for 3 minutes at 3,000 rpm's. Then let it run at idle for a bit and shut off. Did this and it did not work. All other items have set to okay except the VAP which I find to be normal in most cases.
I guess I can go run the engine for 8 minutes and stop without using the brake, then sit for 2 minutes with the service brake on in drive. Then drive home.
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Saturday, May 30th, 2020 AT 5:45 PM
Tiny
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Okay. This is what I was saying that this process of running at 3,000 RPM's for 3 minutes and then idling and shutting off is not the actual process.

If you want to force this monitor to run you need to do the following in this order. So if you can't do it in this order where you live, you need to drive somewhere that you can and shut the engine off and start the process.

1. Turn off all accessories, AC, blower fan, etc.
2. Start the engine and allow it to idle for 2 minutes.
3. Accelerate at part throttle to 55 mph and maintain 55 mph for 8 minutes.
4. Brake safely to a stop.
5. Idle the engine for 2 minutes leaving the engine in drive and the parking brake on.

At this point, the monitor should pass. If not, there is most likely a pending DTC that could be causing an issue.

Just want to stress that if you do what you said which is run the vehicle for 8 minutes, stop without the brake, and let is sit for 2 minutes with the service brake on is only part of the process. If you do it this way, it will not pass. It is only going to be forced to run if you follow the process step by step. See the attached for the actual document. The reason this is so critical is the PCM has been programmed to look for these steps to be followed in order to determine if the monitor passes or not.

Let me know if you have questions. Thanks
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Sunday, May 31st, 2020 AT 9:58 AM
Tiny
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Okay, I can do that. The part that I have seen on a couple of forums is that you have to coast to a stop and not use the brake to stop but use the parking park if necessary to stop the vehicle. Your saying that using the brake to stop is expected by the PCM and then set the parking brake and let it idle in drive for 2 minutes. That is much easier than trying to coast to a stop with the help of the parking brake instead of the regular brake. Will update if it works. So far no codes and all the trim data and o2 voltages etc, are working as expected.
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Sunday, May 31st, 2020 AT 10:27 AM
Tiny
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Sounds good. Yeah. I don't know if the PCM is expecting to see brake input as part of the process but I do know that it says to brake safely so using the brake is acceptable if not expected. I say that because I am not sure why a catalyst monitor would need to see the brake input. So that means it most likely is part of the process because they don't want to put you in a position where you have to coast for that long.

Plus these monitors are meant to run while you are driving normally. This process exists so that if a car has to make it through inspection and the monitor has not run, it can be forced. If you had to wait for it to run normally it could take weeks and you would miss the inspection cutoff.

So if it runs under normal driving and coasting down from 55 mph with no brake input was part of the process, it would never run. I don't know about you but how often do you coast from 55 mph to 0 with no brake input or using the parking brake to slow down? Again there is a lot of good info on forums but unfortunately there is some not so good info as well.

Thanks for the updates. Let us know what happens after you run through this. Thanks
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Sunday, May 31st, 2020 AT 3:33 PM
Tiny
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Thanks for the reply. My thoughts exactly. I have everything else running great. Idle, fuel trims, O2 sensors replaced and voltages looking great. I think a run following the process will get this working. Sure have learned a lot about fuel trims and sensor voltages etc. More than expected. I have been looking for a good OBD2 monitor that will show real time monitoring with graphs instead of text. Actron seems to make one that is not expensive. I tried one of those FIXD monitors since they had them on sale for $20.00 and now I know why. To see anything that matters you have to subscribe to their service. It is a hook you and then fleece your wallet.
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+1
Sunday, May 31st, 2020 AT 6:21 PM
Tiny
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Okay, finally got the catalytic converter to go okay so the only one not okay is Evap. I had to run the process twice before it flipped. So went to smog placed and got it to pass. Still runs slow idle around 400 to 500 rpm's. After getting home it actually flipped a code pending for slow idle (IAC) setting. Now here is what gets interesting. I went in with my scanner and cleared the code. Went back and looked at the Readiness and the catalytic converter, O2 and heater are all back to not ready. Is that normal after you clear a code? I also have to figure out why it idles so slow.
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Monday, June 1st, 2020 AT 3:14 PM
Tiny
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No. It is not unless when you reset the code you cleared the adaptive numerator. When you do this, it wipes the monitors.

Let's start a new post for the IAC issue as we have to keep it to one topic per post. Let us know what the code is and we can figure that out. I would not worry to much about the monitors at this point if you passed smog. They will run on their own well before the next check.

https://www.2carpros.com/questions/new
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Monday, June 1st, 2020 AT 7:43 PM
Tiny
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Okay, the idle seem to all of a sudden work properly. Guess it just needed time.
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Monday, June 1st, 2020 AT 8:55 PM
Tiny
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Haha. I love it when that happens. If it happens to present itself again please come back to 2CarPros. Thanks for the update.
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Tuesday, June 2nd, 2020 AT 6:28 PM

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