BX 16 Engine light idle fluctuate

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Glenn_a
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BX 16 Engine light idle fluctuate

Post by Glenn_a »

Hi tech people, I am new here and not familiar with this Citroen BX 16 petrol and need your help...

I am having issues with the idle fluctuating, I have replaced the idle control valve and checked for any vacuum leaks (smoke test) plus service injectors and checked the AFM and found the flap slightly open and close the same rhythm with the idle I assumed it's not normal and thinking could be just electrical or faulty sensors. Oh, it smells very rich from the exhaust...
I have noticed the engine light was ON as well but not too sure how I can check the error (codes) I'm assuming there is a plug with two pins but could not find it anywhere in the engine bay.
[from the start before I replaced the Idle Contol Valve the idle was worst (engine cuts off plus hard to start and fluctuate when it running] After replacing the Idle control valve first-morning cold start idle is fine soon it warmed up then the idle issue starts (idle fluctuating)...

please help if there anyone had this issue before or at least what to look for thank you!

RobC
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Re: BX 16 Engine light idle fluctuate

Post by RobC »

Hi Glenn and welcome. I’m not clear which engine you actually have. What country are you in?

Do you mean a 16v (which is a 1.9) or an actual BX 16 (which is a 1.6)?

In the U.K. the 1.6 engine only appeared with fuel injection very late on in its life, so I assume you are talking about the 1.9 16v.

The 16v is notorious for a lumpy idle- there are myriad things that can cause it.
Reading the error codes depends on which ECU you have as well, so we will also need to know the model year.
1991 Citroen BX 16v

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

Thank you for your reply RobC

I have 1989 model and it says BX 16valve, hope that helps..
About ECU type pls let me know what to look for to find what type and please what are the list to look for possible cause all this head ache, I am keen to find out.
Thank you so much 🙏

RobC
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Re: BX 16 Engine light idle fluctuate

Post by RobC »

In that case you have the BOSCH motronic ML4.1 ECU.

There are many threads about lumpy idle for this engine both on this and on the bx16v.com forum- I would search for “lumpy idle” in the forums and read through all the advice and act on it accordingly, then come back to us once you’ve exhausted all of that.

It’s a very common problem in this highly tuned engine but there are many potential causes and the chances are you have more than one thing that’s wrong (which always confuses things further).

I’ve never entirely solved the lumpy idle on my 16v: I accept that it’s going to always run a little rough at idle and no longer let it bother me- as long as it pulls as it should throughout the rest of the Rev range. Though of course if it’s really bad then something will be able to be tweaked
1991 Citroen BX 16v

RobC
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Re: BX 16 Engine light idle fluctuate

Post by RobC »

Btw the 2 pin diagnostic socket for Ml4.1 ECU 16v is in theory to be found on the left of the engine as you look at it (ie cambelt end), near the engine mount.
1991 Citroen BX 16v

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

RobC wrote:
Tue Sep 07, 2021 3:51 pm
In that case you have the BOSCH motronic ML4.1 ECU.

There are many threads about lumpy idle for this engine both on this and on the bx16v.com forum- I would search for “lumpy idle” in the forums and read through all the advice and act on it accordingly, then come back to us once you’ve exhausted all of that.

It’s a very common problem in this highly tuned engine but there are many potential causes and the chances are you have more than one thing that’s wrong (which always confuses things further).

I’ve never entirely solved the lumpy idle on my 16v: I accept that it’s going to always run a little rough at idle and no longer let it bother me- as long as it pulls as it should throughout the rest of the Rev range. Though of course if it’s really bad then something will be able to be tweaked
Thanks, heaps RobC...
ill try to search again, it seems no one can get straight answers and never had a successful final word from what they did to solve the issue but ill try to dig more...
may I ask what is "anti-stall setting" is that mean an Idle screw to control the throttle flap?

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

RobC wrote:
Tue Sep 07, 2021 3:55 pm
Btw the 2 pin diagnostic socket for Ml4.1 ECU 16v is in theory to be found on the left of the engine as you look at it (ie cambelt end), near the engine mount.
sorry couldn't find this two-pin plug, do you have a picture what it looks?

how can I post or insert pictures here?

thanks, again!

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

I have noticed too that the oil temp gauge not working and possible the switch is faulty, do you think it would cause an issue on the idle???

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Dave_16v
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Re: BX 16 Engine light idle fluctuate

Post by Dave_16v »

Hi Glenn,

I have just looked at mine (non cat), this is the only 2 pin plug I can see. Check by the two relays on the O/S wing. I understand some are green but that could be the later M1.3.


Image

There are various sites showing the codes but the procedure is as follows.

Taken from an Ausiefrogs written by Barryg. I believe the small diagram is a little misleading but you should get the idea.

Locate the 2 pin diagnostic connector. Stick a wire into pin 1. Pin 1 is as shown below:

---_---
| x x | Looking at the pins, keep notch to the top, pin 1 is left hand pin.
-------
^ pin 1

Using the wire attached to pin 1 as shown above, do the following:

1/ Turn ignition on (but don't start the engine)

2/ Ground pin 1 using the attached wire for 3 seconds. This means touch the wire from pin 1 to some convenient chassis ground point for three seconds, then disconnect from ground. One could connect a switch (one side pin 1, other side chassis ground) for this purpose, but I found just touching the wire on something chassis ground worked fine.

3/ You should see the code 12 flashed on the check engine light

4/ wait until the check engine light is lit continuously. This is about 3 seconds after the code has flashed.

5/ ground the wire from pin 1 again for 3 seconds.

6/ The next stored code will be flashed, or the code 11 is flashed indicating end of stored codes.

7/ if not code 11 repeat steps 4-6.

8/ Once code 11 has been flashed the ECU can be cleared of stored codes by grounding the wire from pin 1 for 10+ seconds when the check engine light is lit continuously.

9/ For an ECU with no stored codes this process will yield code 12 followed by code 11.

10/ Not all error conditions will result in the check engine light coming on whilst driving, but the codes will be stored. Thus, this may be a worthwhile thing to do every so often just to make sure all is well.
Prefer it to the Lamborghini, like Signor Gandini!

RobC
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Re: BX 16 Engine light idle fluctuate

Post by RobC »

Yes that’s the one, thanks Dave.

As for the oil temp sensor- don’t worry about that, it’s completely separate from the engine management loom and so will have no bearing whatsoever on the running of the engine.

Lumpy idle on a 16v could be anything (plus a combination of) from this non-exhaustive list:

Weak spark (leads, cap/rotor, module, coil)
Bad fueling (injectors, fuel filter, pump, fuel grade, etc)
Dodgy electrical connections, especially earthing
Malfunction in engine management sensors- coolant temp, air temp, crank sensor, air temp sensor, air flow meter, idle valve, etc etc (NB these are separate to the dashboard gauge feeds- easy way to tell the difference is the engine management ones all have two pin (minimum) connectors while dashboard ones have only one- other than the oil level one on the back of the block).
Blocked air supply
Vacuum leaks
Timing slightly out
Poor compression on one or more cylinders

Etc etc.

So it’s unsurprising that you can’t find a straight answer. What you need to to is work methodically through each item and either discount it or fix it and then move onto the next.
1991 Citroen BX 16v

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Dave_16v
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Re: BX 16 Engine light idle fluctuate

Post by Dave_16v »

Add throttle position sensor to ROB'S lot, has that been checked whilst doing the AFM and ICV.
Prefer it to the Lamborghini, like Signor Gandini!

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

Thanks Dave_16v and RobC for all your effort to help 👌 ill look into that RobC check list and go from there but for now need to know the error code and need to find that plug. Dave_16v mentioned some are green color? I think I found that plug and it looks like a injector plug just sitting on the RH near engine mount. I wish I can attach pictures, how you guys can attach picture anyway? Thanks again🙏

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Re: BX 16 Engine light idle fluctuate

Post by panky »

I use Imgur to host my pictures. I load them up to my computer from my camera/phone then download them to Imgur, I'm pretty sure you can load them direct from your phone but I've not personally done that. Easy to set up an account, and it's free, and super easy to load a link onto the forum by copying the BBC code (it becomes obvious when you have an account)and posting it into a reply on here.
Image

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Dave_16v
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Re: BX 16 Engine light idle fluctuate

Post by Dave_16v »

Make sure you select full editor / preview when you reply.
Under the text section below save as draft you will see "Attachments".

Click that and you will be able to browse your folders and select the photo. Upload it then select place in line.

Have your cursor in the position you want to attach the photo. Officially, in the comments part, you add your user name and "own copyright".
Prefer it to the Lamborghini, like Signor Gandini!

Glenn_a
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Re: BX 16 Engine light idle fluctuate

Post by Glenn_a »

thumbnail_20210909_154858.jpg
is this the diagnostic connector? (green in colour)