P0402 Air Circuit - Air Flow Lower Than Recommended Citroen C5 X7 1.6 HDi

[carlsberg101]

After 6 months of relatively uneventful motoring the car has recently thrown up a host of problems, this being the latest one.

It only just went through it's MOT last week when they fitted a new Mass AirFlow Sensor when the engine management light came on on the way to the garage.

2 days after the MOT it decided that it would occasionally be very sluggish to pull away. It will not rev above 3000rpm and simply has no acceleration so I have to crawl away from traffic lights etc. with a maximum speed of 20 mph, but then a minute later it is absolutely fine and accelerates and pulls away as normal.

Plugged in to Diagbox thingy and the above code pops up. Mechanic Google suggests it's possibly the EGR valve so I pop it off expecting it to be clogged like all the Youtube videos but it actually looked surprisingly clean inside. I give it a clean anyway and pop it back on only to have exactly the same symptoms and code, except the code is now intermittent rather than permanent.

I suppose the EGR valve could be faulty. I did think that the action of the valve was not as smooth as I had expected but as it was my first encounter with an EGR valve what the hell do I know.

This might be a random thought but in the back of my mind I'm thinking turbo? Probably just because I'm paranoid when it comes to turbos as car is currently on its third one. The turbo does seem to get insanely hot and I did notice that it has a slightly louder whine/whistle the other day when accelerating before these new problems cropped up. I took off the air intake and turbo is still spinning but I'm worried it is on the way out again. I'm planning to take the turbo out and inspect it and check the oil pipe is clear but does anyone have any words of wisdom they would like to share?

Thanks

[carlsberg101]

I thought I should do a quick update.

I removed the turbo and oil feed and they looked OK so I decided to bite the bullet and replace the EGR valve. As I wasn't convinced that it was the EGR valve causing the problem I opted for the cheapest one I could find. End result, new EGR valve fitted and it didn't make a blind bit of difference.

Next plan is to replace the Turbo Boost Solenoid. I've ordered a reconditioned unit reasonably cheap so it is probably worth a go. It does make sense as it does feel like a lack of boost hence why I had my suspicions about the turbo. After that it is a matter of checking the vacuum lines but I don't see how a damaged vacuum line would only cause an intermittent fault?

Watch this space.

[Doo]

Have you looked for bad hoses? The boost hoses tend to break down inside due to oil passing through them and the can collapse without any outward signs. Squeeze the hoses at the air metering unit (where the boost hoses go into the inlet). Check the corrugated hoses as they are the first to go, especially the (as you're facing the engine bay from the front of the car) right side from memory....

If any of them feel squishy, pop it off and check the inner lining for tearing. It'll be pretty obvious.