Lexia Richness Regulation Fault Intermittent wiht C5 1.8

[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?

[Mandrake]

"Richness Regulation" is a bit vague on it's own unfortunately. Is it too lean or too rich ? At idle or at high rpm ? Are you sure there wasn't another fault code ?

It could be many things - some things I would check first are long term fuel trim at both idle and higher (2500-3000rpm) to see if it is running lean or running rich.

Also check for oxygen sensor activity - make sure its switching back and forth high/low at idle and during a steady light to medium throttle cruise.

If it's always ok when you accelerate hard but has intermittent problems when you're cruising with a light throttle there could be an oxygen sensor related problem, possibly an intermittent one.

Unfortunately it's going to need to go back on the Lexia and capture some live data including while driving the car.

[agaafear]

Thanks for that. It's hard to explain! It's generally when I'm driving in traffic (under 30mph) and I let the throttle off and then reapply lightly - the engine jerks and then clears and runs fine. If I floor the throttle it accelerates without hesitation or any misfires. I'm not sure if the lexia message and this are related - I suspect they are.

So I need to test the sensor - is this with the lexia system while driving the car?

[agaafear]

This site is pretty useless.

[Hell Razor5543]

This site is pretty useless.

I would not say that. If nobody else has had this problem then nobody else can advise you on how to resolve it. The worst part of your problem is the word 'Intermittent'. Ask any engineer in any field of engineering what is the worst type of problem, and I guarantee they will say 'Intermittent fault'.

[Hell Razor5543]

Thanks for that. It's hard to explain! It's generally when I'm driving in traffic (under 30mph) and I let the throttle off and then reapply lightly - the engine jerks and then clears and runs fine. If I floor the throttle it accelerates without hesitation or any misfires. I'm not sure if the lexia message and this are related - I suspect they are.

So I need to test the sensor - is this with the lexia system while driving the car?

You can run the car with the Lexia connected, but it depends on where the diagnostics port is in relation to the driver and their needs. For example, the port on my Xantia is down by my right knee, and having the cover open and the cabling passing near my legs would cause me concern whilst driving. However, on my company van the port is in the glove compartment, and would not cause any issues.

When the spark plugs were changed were they replaced with identical plugs, or 'compatible' plugs? Citroens can be picky, and compatible plugs that are supposed to work don't always have the same results as the manufacturer recommended plugs. If you read through Mandrakes' massive thread he appears to have had issues with spark plugs.

[agaafear]

Fair enough!

[bobins]

When the spark plugs were changed were they replaced with identical plugs, or 'compatible' plugs?

There's also been a load of fake NGK spark plugs doing the rounds over recent years - they're extremely convincing to look at, but go dodgy after a short time. I'm in no way suggesting you've fitted dodgy plugs from NGK or anyone else - but it's another avenue to explore.