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Recently had to install a catch can. Sent it to the shop and they recommended putting one on because I was having a issue with oil leaking. They found it and wanted the catch can added. Since I added it, I went on a 200 mile cruise yesterday and at the end of it my idle was running high. Usually it’s around 750 and it was staying around 2000 for extended periods of time So my question is, would adding the catch can have anything to do with the idle. I ran longer tubes bc I had only one location that would fit this catch can. Sorry if this is stupid but when I change something and something Else happens then 2+2 =4. Most of the time
Not a big fan of the setup but I can't really tell from the pics how your system is routed but it looks like you have the TB capped off and the intake and clean air side of the valve cover going to the CC. What's going on with the other two ports on the VC's? If this is an LS1 then you should have two ports on the passenger side and one on the rear of the driver side VC. In stock form the the rear of both VC's connect to a hose running up to the intake manifold where a PCV valve is in the line just before entering the intake manifold. If there's a leak in the line leading into the intake manifold it will cause higher than normal idle.
If it were me and I needed to run a CC then I would have left the lines as stock but ran the lines connecting the two valve covers to the CC and then from the can through the inline PCV valve and then into the intake manifold. As for the other port on the passenger side it should be connected to the throttle body or the bellow between the MAF and TB.
From what I can tell they’re no pcv just straight vacuum to the can then cover. I would put a pcv valve in the line coming off the intake before the can. The high idle is probably one of the back ports aren’t sealed and it’s got vacuum on the crank case.
There should be a pcv valve in the line from the intake manifold to the catch can. It's basically a vacuum leak without it. What happened to the stock one? You should be able to plumb that into the line.
After looking at the pictures more carefully 01 camarosstx is right. It looks like you have the supply air tube from the throttle body capped off That port is where the supply of clean air into the engine comes from. If the supply air tube is just vented to atmosphere you are using unmetered air which can cause issues too.
There should be a pcv valve in the line from the intake manifold to the catch can. It's basically a vacuum leak without it. What happened to the stock one? You should be able to plumb that into the line.
This remains true, however. My factory PCV grommet disintegrated between the catch can and the TB, so I drove it for a couple of days with just a hose and no PCV valve before I could fab something up. The effect was just as the OP describes - like having a big vacuum leak.
Ok I added the PCV valve back in line on the inlet side of the catch can. And then I connected the hose from the passenger side valve cover front 90 to the throttle body. Not sure why this was off. Don’t know if the shop took it off and didn’t forgot to put it back in or left it off for whatever reason. Today I will get out and see if that makes a difference.
when I took it out Sunday I drove about 2-3 miles with everything ok, and then it felt like my foot was on the gas pedal gradually climbing the rpms up even though my foot wasn’t on the gas. I put it in neutral and then it idle up to 3k rpm for a bit. Then went back to down to normal idle after a minute. So I drove it home and parked it. Haven’t drove it since I put the throttle body line and PCV valve back on. Hopefully this helps.
You are getting closer. The pcv valve might need to be in the hose that goes from the intake manifold to the catch can. Many cans are not sealed. I would move the valve so that it is between the vacuum source and the can to eliminate the possibility of the can itself being the vacuum leak.
this is how I have it running. So should I move the PCV valve? I have it coming off the long line coming from behind the top back of the intake (where the two PCV lines come together). Sorry, just trying to get it right. .
also in here I put the line from the throttle body to the valve cover? That is good to go? How I have it is how it should be? Thanks again any and everyone for any help
the catch can is sealed pretty good. O-Rings on the parts with arrows and hose clamps on the hoses. So the catch can should be sealed pretty good
Originally Posted by jlangley
You are getting closer. The pcv valve might need to be in the hose that goes from the intake manifold to the catch can. Many cans are not sealed. I would move the valve so that it is between the vacuum source and the can to eliminate the possibility of the can itself being the vacuum leak.
The line from the throttle body to the v/c is correct.
If the catch can holds vacuum you should be good as is.
Personally I would move the pcv valve to between the can and intake to be sure.
ok..... so you would move the PCV valve to the exit side of the catch can. So come out of the catch can (on outlet side)/PCV Valve/ then go into the intake? I’ll look into that.
I put the catch can there bc it’s where I could mount it without doing much modification. But I wonder if I got a tall skinnier one that I could fit closer to the throttle body/intake area. And mount it there and it will shorten the lines going to both and maybe that would be good? Not sure if the longer lines have any negative effect on it.
Originally Posted by jlangley
The line from the throttle body to the v/c is correct.
If the catch can holds vacuum you should be good as is.
Personally I would move the pcv valve to between the can and intake to be sure.
I would move the pcv valve in case the can won't hold vacuum.
The length of the lines shouldn't be an issue.
Make sure the valve is installed in the same direction as stock. It's basically a check valve.
Not sure which PCV valve you are using. The OE one had a check ball in it. Later models had a small hole opening. I tried the later one on my car and the idle got wacky.
I switched to the newer version many years ago and have used it ever since without noticing any difference.
And yes, the PCV needs to be on the outlet line from the can.
I wonder if proximity to the intake could make any difference? I can't think of a reason why it would, but that seems to be a difference between the OP's set up and what the rest of us run.
just original PCV valve. Moved to out line of catch can going to Intake.
Originally Posted by RevGTO
I switched to the newer version many years ago and have used it ever since without noticing any difference.
And yes, the PCV needs to be on the outlet line from the can.
I wonder if proximity to the intake could make any difference? I can't think of a reason why it would, but that seems to be a difference between the OP's set up and what the rest of us run.
not sure yet, weather has been crazy here and haven’t got the car out to fully check. I started it and let it idle and it idled much better but the true test will be when I have a chance to put miles on it. But hopefully the problem is solved. Just need to shorten the hoses and move the catch can so it’s not so far away. I’ll keep this thread posted when I get more updates.
Originally Posted by jlangley
Is the original problem solved now?
Last edited by JaceDaniel83; Feb 12, 2021 at 06:06 AM.
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PCV. Catch Can. Idle changes 
