Hunting for an air leak

[Any1else]

Trying to get to the bottom of a P0171/P0174 fault code and so far have:-

1. Smoke tested and found a leak in the throttle body/idler valve hose and replaced it.
2. Replaced the CCV hoses and found that the small stub on the CCV didnt have a blank end on it so I installed one.
3. When the intake manifold was off I replaced the gasket on it as well as the one on the throttle body.

After about 150 miles it threw the codes again so I :-

4. Replaced the gasket on the DISA
5, Double checked all the hoses and clips.

When the car is idling, and when its is revved gently, I can hear a intake/sucking sound from the back of the intake manifold (when I am under the bonnet) but as this aligns with the throttle body I am wondering if this is just the normal intake noise. Anyone else notice this on their car to give me a point of reference?

Going to run another smoke test when I get a chance but I cant see where else there might be a leak.

Do the injector seals perish enough to allow air in? Should they be on my replacement list?

 

[enuff_zed]

I assume you have thoroughly checked the corrugated pipe on the inlet elbow?
Could be split underneath where you can't see it?

 

[Any1else]

I assume you have thoroughly checked the corrugated pipe on the inlet elbow?
Could be split underneath where you can't see it?

Yup. It’s been off a few times and it is fine. I noticed last night that the coupling to the throttle body pipe wasn’t straight so have now aligned it properly so it may have been the cause of the recent code but will need 150 miles or so to be sure.

Main question is - do I have an air leak or does the throttle body normally make a sucking sound?

Going to see if I can check the fuel pressure to make sure the codes are because of too much air and not because of too little fuel.

 

[colb]

Often missed are the blanking rubber caps at the rear underside of the intake manifold if you have these they perish split and fall off. Also check the dipstick tube O ring has not failed and allowing air in. Smoke should find these if they are at fault.

 

[Any1else]

Often missed are the blanking rubber caps at the rear underside of the intake manifold if you have these they perish split and fall off. Also check the dipstick tube O ring has not failed and allowing air in. Smoke should find these if they are at fault.

Cheers colb, when I had the manifold off last week I checked the caps and they were all present with no signs of perishing. Also, dipstick o-ring was replaced when I had it out.

 

[Mike6]

Similar problem to me but my codes appeared just after garage struggled to replace post cat oxygen sensors and had to use a lot of heat. I am still adamant that sensors might be letting air in or they disturbed that troublesome exhaust joint next to the sensors. Either way it's another possibility for showing codes

 

[Any1else]

Thanks Mike6, I did wonder about the sensors but given the price of them I want to rule out an air leak before attacking sensors. Still curious about how loud the intake noise should be on a throttle blip.

What was the reason for you getting the sensors changed?

 

[Andrew J]

I've chased these codes recently and from research the rocker cover gasket and oil cap seem to be suspect items too. Smoke test should show these though.

 

[Mike6]

I was getting a specific code for the sensors. Heater element had failed on one bank of oxygen sensors so doubt it's a failing sensor on your car but could be air getting in if exhaust joint is failing.

 

[Any1else]

Andrew J, the oil cap was on my list too but the vacuum pull on it when the car was running was noticeable without any sucking sound. I haven’t checked it since I’ve replaced the CCV parts but will now. Rocker cover gasket was leaking and dripping oil onto the exhaust so I have replaced it so can rule that out.