1998 V70 rough idle after PCV replacement

[erikv11]

Don't mean to be a broken record (I know ... "what's that?"), but did you check the corner of the intake manifold nearest to the throttle body?

[charleskennedy23]

I had a similar issue with my 98 v70 t5 after doing the pcv. My problem was I didn't get the bracket that holds one of the hoses in the pcv system in place on right. The bracket was on driver side and is behind the intake manifold. If you mess this up the IM will pinch the hose and won't seal. I got a gas smell and the car wouldn't idle at all. I could see the pinched hose if I looked right at it, but would have had a hard time taking a picture of it. RSPI helped me find the issue and he has a warning about this problem in his DIY video on YouTube.

I'm pretty sure that this is what Erik is talking about. If this isn't your issue my guess is that IM isn't sealed in some other way.

[charleskennedy23]

Here is a picture of the hose and bracket I am talking about. This picture was taken before I took the old PCV out. When I put this back together I got the bracket that is holding the PCV hose on the right (driver) side pinched between the block and the IM. I had exactly the same symptoms as you. I took everything apart, got that hose and bracket installed properly, put it back together, and the car ran smooth as silk after that.

[erikv11]

Kudos to Charles for a much better description and an image to boot, that is the bracket I was referring to. They come in a couple different shapes but all can get in the way.

[charleskennedy23]

thanks Erik! That PCV job was the first major job I tackled on any car in my life. Up until that point it was just oil changes, inflating the tires, and the fuel filter. I about crapped my pants when I put it back together and the was doing the stuff bruno was talking about. Not to mention my wife was pretty mad about the gas smell making its way into the house from the garage, lol. I was so grateful when rspi told me about the bracket "gotcha."

Bruno I hope your issue is easier than this because it's no fun taking the IM off again. If this is it then the good news is that conceptually the fix is easy.

Cheers!

[brunocerous]

Here is a picture of the hose and bracket I am talking about. This picture was taken before I took the old PCV out. When I put this back together I got the bracket that is holding the PCV hose on the right (driver) side pinched between the block and the IM. I had exactly the same symptoms as you. I took everything apart, got that hose and bracket installed properly, put it back together, and the car ran smooth as silk after that.

I was so excited to try that, but when I looked, my car doesn't appear to have that bracket at the right-hand (driver) side of the manifold holding the hoses down. From what I could tell, the PCV hose moves OK and doesn't seem to be pinched by the manifold, at least on that side.

Guess the manifold is going to have to come off again. ...

[charleskennedy23]

Well good luck moving forward. I hope you find something when you take it apart. When you pinch the hose like I did the seal between the IM and the block doesn't form and the car runs just like you described. My guess is somehow you aren't getting a good seal. So make sure everything gets sealed tight before you torque down the IM bolts.

Let us know what happens... Def want to get you back on the road soon!

[brunocerous]

Thanks so much, everyone, for all your help, your ideas and your suggestions!

After checking the manifold once again for leaks or pinched hoses and finding none, I had an indie Volvo mechanic look at it. A smoke test determined that the entire manifold was leaking, which vindicates everyone who said it was a massive air leak.

After replacing the gasket and double-checking everything, the car exhibited backfiring through the intake side. A second — yes, second — smoke test determined that the entire top half of the manifold's mating surface was leaking in various places. Checking it with a straightedge, we found that the manifold was warped — only about 2/1,000ths of an inch, but enough to cause a significant air leak.

While the indie mechanic had initially thought that torquing the manifold bolts would be enough to rectify the warping, the fact that it was warped along its horizontal axis rather than vertical made it impossible. The manifold gasket showed signs of pressure on the bottom half, but not the top half.

The solution: Two gaskets, plus silicone on both sides of each gasket, finally stopped the leak. Indie mechanic (specializing in European cars) said that he had never seen a manifold warped like that. (Kudos to the poster who asked if my manifold had come from the junk yard — being that I'm the second owner, it's possible.)

He also found that the spark plugs "were dark," which might have been caused by the oil pressure from a bad PCV, and which would explain why my plugs looked so foul after only a couple of months (previous thread: https://www.matthewsvolvosite.com/forums ... 67#p384167 ). Also, he found that a ground cable under the starter had been severed, which should've prevented the car from starting AT ALL, although it did not. Likely, it was still making contact at some point before all this went down.

A heartfelt thank-you to everyone who offered their time and expertise.

[humbertoflores63]

I have never heard of a warp intake. If the car was running fine before you started the work, how did it warp or could been the torque sequence when you put it together. Did you clean the mating surface of the intake plus the block?

[brunocerous]

I have never heard of a warp intake. If the car was running fine before you started the work, how did it warp or could been the torque sequence when you put it together. Did you clean the mating surface of the intake plus the block?

Beats me. If I had tried to pry off the manifold with a crowbar, that would make sense. I didn't. Indie mechanic said he had never seen that, either, and didn't think it was caused by torquing. I never exceeded the recommended 18 ft/lbs either.

I hadn't cleaned off the mating surfaces as well as I should have, but my guy did clean them off to a near-mirror-like finish. Still, it wasn't flat enough to prevent a leak. I'm not crazy about the two-gasket solution, but I'll definitely keep an eye on it.