'89 BX 16v Error Code 52 - Air leaks?

[Kitch]

In short:

The idle can be smooth in a 16v, you just have to set it up properly. 9/10 times it's because the idle mixture is wrong, which on some models can be adjusted using the adjuster screw on the air flow meter. The cams aren't lumpy or anything, so other than the fact they take gobfulls of air due to the huge valves, they should be able to idle as smoothly (if not smoother) than an 8v.

The gearbox - sounds like the syncromesh is worn. It starts by grinding/baulking on rushed changes, and eventually will grind on all changes into the affected gears. 2nd and 3rd are the ones that are usually affected first, but not always. They weren't like it from the factory, no.

[white exec]

On the gearbox, check that you have 75W80 gear oil GL-4 there, and not GL-5 or GL-4/5.
Total Transmission 8, or Traxium Gear 8, is one of the correct ones.

GL-5 is a lower friction spec, and actually prevents the synchromesh in Citroen's 'boxes from operating correctly, which can lead to baulky changes. Give the new oil a few days of use to bed in. You should notice the difference.

[krekov]

Ah, looks like I'll be shopping for a new transmission in the near future in that case. It's already had an oil change a month ago, the oil used was Total Traxium Gear 8.

In short:

The idle can be smooth in a 16v, you just have to set it up properly. 9/10 times it's because the idle mixture is wrong, which on some models can be adjusted using the adjuster screw on the air flow meter.

I believe that can only be done on non-catalyst models, is there any way to do it on others?
On the old, broken ECU I was able to adjust the mixture using spring tension on the AFM and achieved an idle like this:
https://youtu.be/tudh1Fq4xQc

The AFM in that video is a total bodge job, don't even look at it. I got it idling just as smooth on a different AFM too.

But, with the new ECU it doesn't appear to react at all to these spring tension changes.

[krekov]

Do a compression check.

I was able to do it today, it is as follows:
11 bar on cylinder 1
13 bar on cylinder 2
12.5 bar on cylinder 3
12 bar on cylinder 4

[Kitch]

I believe that can only be done on non-catalyst models, is there any way to do it on others?
On the old, broken ECU I was able to adjust the mixture using spring tension on the AFM and achieved an idle like this:
https://youtu.be/tudh1Fq4xQc

The AFM in that video is a total bodge job, don't even look at it. I got it idling just as smooth on a different AFM too.

But, with the new ECU it doesn't appear to react at all to these spring tension changes.

Fair question, possibly not. It might be that the mixture is controlled by a combination of lambda and coolant temp inputs. Truth be told, I've only ever known of two DFW cars in the UK, so I've never seen one up close to inspect it