High idle after PCV replacement

alphahotel · Post by **alphahotel** » 07 Feb 2011, 15:03

Hi all. I have just recently replaced my PCV system on my 1998 V70 non turbo. My car had stalling problems and after searching the forums I figured this might be the cause. Everything went fine except that once I got my car started it is idling way too fast. It starts at 1100rpm and then steadies at around 1400 rpm once it is moving. Otherwise the car is now running beautifully.

I have read that this might be related to a vacuum leak. To sort it out I started the engine and previously disconnected the plugs from IAC, MAF and coolant temp sensor one at a time. In either case I managed to get the engine revin at around 900 rpm, albeit somewhat erratically, so I discarded the vacuum leak problem although I am not 100% sure.

I have also read this might be related with either a dirty IAC, which I´ve cleaned, a faulty TPS or a busted coolant temp sensor. I would really appreciate if somebody could give me some insight if they have had similar problems.

All the best, Antonio; Madrid, Spain.

FCPEURO · Post by **FCPEURO** » 07 Feb 2011, 16:28

It sounds to me either a vacuum leak or an issue with the IAC. Being the IAC was working before you did the PCV, I would go back to looking for a vacuum leak. Did you remove the intake when you did the PCV?

Post by **jblackburn** » 07 Feb 2011, 16:52

Or something even simpler! The throttle cable may be slightly tighter than it was from moving the manifold around. Pull off the black plastic cover over the throttle assembly and hold it fully closed with your hand. Does the idle calm down to about where it should be? If the arm isn't touching the little idle screw, even in the slightest, the engine will start idling higher - it's very sensitive.

alphahotel · Post by **alphahotel** » 08 Feb 2011, 01:08

FCPGroton wrote:It sounds to me either a vacuum leak or an issue with the IAC. Being the IAC was working before you did the PCV, I would go back to looking for a vacuum leak. Did you remove the intake when you did the PCV?

In order to replace the PCV I had to remove the intake manifold. I also took apart the throttle in order to clean it. Replaced both gaskets in the intake manifold and throttle component. Where and how should I check for a vacuum leak? Thanks.

jablackburn wrote:Or something even simpler! The throttle cable may be slightly tighter than it was from moving the manifold around. Pull off the black plastic cover over the throttle assembly and hold it fully closed with your hand. Does the idle calm down to about where it should be? If the arm isn't touching the little idle screw, even in the slightest, the engine will start idling higher - it's very sensitive.

Hi jablackburn. Indeed this was the very first thing I checked and the arm is in full contact with the idle screw. Thanks.

scumcity14 · Post by **scumcity14** » 12 Feb 2011, 07:18

There is a metal bracket on the drivers side of the head that commonly gets erroneously placed between the manifold and gasket causing a vac. leak...check this. It is the bracket that holds the large PCV line. nonthing should go between the manifold and head except the gasket

Post by **jimmy57** » 12 Feb 2011, 09:05

IAC valve and throttle position sensor leads swapped?

alphahotel · Post by **alphahotel** » 15 Feb 2011, 04:41

scumcity14 wrote:There is a metal bracket on the drivers side of the head that commonly gets erroneously placed between the manifold and gasket causing a vac. leak...check this. It is the bracket that holds the large PCV line. nonthing should go between the manifold and head except the gasket

Nothing but the intake manifold gasket there. Thanks.

jimmy57 wrote:IAC valve and throttle position sensor leads swapped?

I did tag both and I am almost 100% sure they are properly placed. Thanks.

At any rate I did manage to bring my idle back to normal. I actually tightened the intake manifold bolts again this time to 20Nm torque specifications and in the correct star inside to outside pattern. I also replaced a small cracked hose running into the vacuum tree on top of the throttle body. I think this might have been the actual culprit. My revs now read 900 rpm steady after warmup.

Best regards, Antonio.