[Sup3rTallPaul]

My truck is throwing a code for a vacuum leak, and the idle drops pretty frequently when I'm sitting still. I looked around under the hood while I was changing the thermostat, but I didn't see anything that looked like it could be the problem. Are there any usual culprits on our trucks? Its a 2004 i4, base model. It's had this problem since I got it which was about two months ago.

 

[cart7881]

What's the code for "vacuum leak"?

 

[jfh2004gmc]

check your resonator hose up top. our engines are what they call a closed orifice system. there is another hose also that requires full replacement of the intake manifold. common problem. had mine done at the dealership. cost me about $600 .

 

[Iceman62]

^^^Yes^^^

Also, vacuum leaks can be tough to troubleshoot as it could be anything from a pinhole to hidden crack (dry rot). One of the easiest methods to locate is have your truck checked for leaks at a service ctr...cheaper than going out and purchasing necessary equipment to determine the cause. I let the experts find it...not as easy as the old days when hoses simply broke in half. Good luck.

 

[Sup3rTallPaul]

What's the code for "vacuum leak"?

It's actually two, P0420 and P0506

 

[Sup3rTallPaul]

check your resonator hose up top. our engines are what they call a closed orifice system. there is another hose also that requires full replacement of the intake manifold. common problem. had mine done at the dealership. cost me about $600 .

Do you have a picture or diagram of where the resonator hose is?

 

[Uncanny355]

I don't have the resonator anymore but this might give you an idea. You have to pull the resonator to get to it. Where my finger is pointed is where it connects

 

[Sup3rTallPaul]

I don't have the resonator anymore but this might give you an idea. You have to pull the resonator to get to it. Where my finger is pointed is where it connects

Ah okay thanks!

 

[Sup3rTallPaul]

Alright I checked the resonator hose and it looks good. I checked other possibilities around the throttle body and intake and I can't find it at all. So, I have a question. Is it common for the intakes to leak on the 2.8?

 

[Freeballin]

I would clean the throttle body & air mass sensor before searching for vacuum leaks.

 

[Sup3rTallPaul]

I would clean the throttle body & air mass sensor before searching for vacuum leaks.

Would that trip a vacuum leak light?

 

[Freeballin]

Would that trip a vacuum leak light?

If you're referring to that red colored vacuum cleaner symbol in the instrument cluster display?



J/K

 

[Freeballin]

That P0420 code is a catalyst efficiency fault that can be triggered for many reasons.

The P0520 code is for the idle air control (IAC) system rpm lower than expected during cold start up.

What makes you think there's a vacuum leak?

Is this a stock engine with no bolt-on mods?

 

[Sup3rTallPaul]

That P0420 code is a catalyst efficiency fault that can be triggered for many reasons.

The P0520 code is for the idle air control (IAC) system rpm lower than expected during cold start up.

What makes you think there's a vacuum leak?

Is this a stock engine with no bolt-on mods?

The little print out Auto Zone gave me with the codes both had Vacuum leak listed as the issue. That's why I thought that.

 

[Freeballin]

Cleaning the throttle body & mass air flow sensor will most likely cure this problem.

Code P0506

Code P0420

How To: Change Spark Plugs & Clean The Throttle Body

How To: Clean Your Mass Air Flow Sensor

Walmart CRC cleaner pack $7.88
.