06 Explorer 4.0 V6 - small vacuum leak?

[V8SHO]

Hi everyone,

I've been having a bit of trouble figuring out the cause of a rough and high engine idle at cold start with my 06 Explorer. When the engine is warm, engine idle is smooth and runs fine otherwise.

I hooked up a scan tool and have no stored or pending codes so I looked through the live data for clues. The only thing I noted is that the long term fuel trim is about +10% at idle on both banks, indicating a lean condition. Short term fuel trim is at 0. When applying throttle, long term goes to 0.

I assume there is a small vacuum leak somewhere, but I can't find anything obvious. The vacuum lines on the passenger side near the firewall look good, intact. The other larger hoses near the driver side also look fine, nothing broken/melted. I sprayed a bit of throttle cleaner along the intake manifold and gasket area, injectors, vacuum lines, and other sources of vacuum, but no change in rpm.

I also checked the pcv valve; I wasn't quite sure how to test it, but I removed the pcv hose from the intake manifold and covered the vacuum port on the manifold with my finger but the engine idle was still rough. If it were the pcv valve, covering the port should've made the engine run smoother, right?

Are there any other things that I should check? Perhaps there is something I'm missing?

Thank you for your time and appreciate any input in advance.

 

[Rcflyer330]

you say it has a high cold start idle. how high is the idle?

 

[V8SHO]

At cold start it idles around 1600rpm, fluttering. Before this problem started it used to idle at about 1100 cold, and then drop fairly quickly.

 

[Flag Gibby]

Interesting, at idle cold it should be around 1100 like it used to be. I am thinking that it might be some piece of rubber transition/connector in the vacuum system that has a hair line crack in it that seals once it gets hot. You could try spraying the connections with starter fluid to see if that causes the idle to change indicating what transition is leaking when it is cold. I would start with the PCV valve connections since those are a known issue on older vehicles. I believe that if you disconnect the PCV valve you need to plug both the tubing and the valve. As far as testing the PCV valve you should be able to get air flow through it one direction only and if you move the air direction in to out very quickly you should hear the diaphragm moving back and forth in it.

 

[V8SHO]

Thank you for the reply, I really appreciate it!

Now that you mention it, I recall there is some noise coming from the pcv hose at the intake port connection, like a very faint hissing air noise. I sprayed that connection and surrounding area with throttle cleaner but didn't notice any change in rpm though. Maybe the only way to find out will be to change them out anyway.

There isn't a lot of working room at the pcv valve area, after removing the hose at the intake port, does the pcv valve need to be rotated out or just pulled?

 

[Flag Gibby]

On the V8 they don't come out, but on the V6 it is just pressed in to the valve cover.