Lexia - Richness Regulation Fault Message - C5

[agaafear]

My C5 1.8 has 53,000 miles and runs well. However, recently, I notice that when I'm driving on a light throttle or let the throttle off to reduce speed, the car starts jerking quite strongly. In traffic this is quite annoying. My friend who works for Citroen did a diagnostic test using Lexia and "Intermittent Fault, Richness Regulation" appeared. It did not throw up any code. The car has recently been serviced - including new spark plugs. My friend describes the jerking as an intermittent misfire. The car accelerates without any issue and otherwise runs fine. Any ideas what the cause of this might be?

 

[paul.h]

As a first step I would check the air filter is clean and then clean the throttle body and plate using something like carb cleaner or white spirit since this can affect low engine speed.

[agaafear]

Thanks Paul - I'll do this. I noticed that the throttle cable, where it enters the throttle, seems quite loose. It comes up very easily when pulled. The pedal itself is fine. If it's neither of those what would you look at next?

[MadMalx]

Throttle cable will be slack, you adjust it by getting someone to put the accelerator to the floor then pulling the cable to take up the free play, then insert the clip. Once done the cable feels slack under the bonnet without any tension applied.

My 1.8 exhibits the same fault as yours, again without any codes being shown up. Suggestions I've had were coil pack, dirty injector or maybe a sticky EGR valve.

[qman3428]

It probably wasnt done in the service so change your fuel filter

[agaafear]

I perhaps didn't explain the problem properly! :)

 

When I'm driving in traffic (under 30mph) and I let off the throttle and reapply lightly the engine jerks a few times and then runs fine. I also notice when I start the car and it's warming up - when I'm stopped - the idle is a bit lumpy and you can fee it in the car... The car hadn't been used much - laid up since December last, only every covered about 4,000 miles per year and was driven very gently.

 

One other thing - the NCT (MOT) - last year the rear anti slip alignment test : the limits are +14 to -18 m/km. The car was exactly at -18. I am told there are no adjustments that can be made to the rear of the C5, there is no play in the bearings, the car feels absolutely stable and the tyres are wearing evenly. I was under the car recently and am amazed at how clutter free the suspension area is - quite amazing how a single sphere on each side operates the rear suspension!

[agaafear]

Is the fuel filter bothersome to change. I recall on the Focus that it was a bugger to get at! The air filter was changed at the service!

[paul.h]

Have you cleaned the throttle body and plate yet, I normally do this each time the air filter is changed since the carbon that builds up affects the gap between the 2 so the air flow is not correct and the idle motor has to try to compensate.

[agaafear]

It was the idle air control valve which is attached to the throttle. Following this, garage did a reset of the "auto adaptives" - seems to be running fine now! The slight whistling noise from the top of the engine at idle - or a little more - is nothing to worry about.