RS2 Rough idle

[igor136]

It can be crack on exaust manifold.

1-2-4-5-3

[s0_big]

I guess you could compare the RS2 maf with your AAN maf on the AAN if thats running ok. That should give you a better comparsion as to its condition. There is no electrical difference between them. The RS2 ecu has a change internally which gives a different reading compared to for example the AAN. If it runs ok on the AAN and is within spec more or less considering its age then you have eliminated one more thing. If you use the AAN maf on the RS2 and the problem is on the car we haven't eliminated it. So get readings from AAN first then swap to RS2 .
I can't remember exactly the calculation for coolant temp but if in group 000 field 1, 184 - 215 represents 85C - 105C, surely 161 should be more than 25C! Would have thought they both read from the same sender. Does it make sense when engine is warmed up?

The MAF is sure working, i tested 2 AAN MAF that i know is working but no difference. The readings from VCDS (group 3) that is the air intake temp, sorry my fault. The coolant temp sensor is working, showing in spec and also in the right Ohm values.
Tonight i changed the FPR for an AAN (4.0bar instead of 3.8bar) no difference what so ever..
I have this one question that i would like to have answers to though, why is it that the car runs on good idle for those 40-60sec right after cold start up, and then changes to this ****** idle. It must be some electrical/sensor problem i think. I assume that the ECU is running first say 60 sec in a predicted maner and then starts to look/get input from some sensors to control the engine..

[twoqu]

Yes you are right despite it clearly saying Coolant temp in red! Thought it was a bit odd!
I think it has something to do with lambda heating. I can't see the engine getting to 60C in that amount of time to be honest. The engine could be at minus C.

[s0_big]

Yes you are right despite it clearly saying Coolant temp in red! Thought it was a bit odd!
I think it has something to do with lambda heating. I can't see the engine getting to 60C in that amount of time to be honest. The engine could be at minus C.

It's me that did the writing in red. What do You mean getting to 60c in that amount of time?

On Sunday I have thoughts of plugging in my Maxxecu and see if I can see something strange. Little easier to get info from that ecu.
Really appreciate the help you have given so far

[twoqu]

It's just I read that Motronic goes from open to closed loop at coolant temp of 62C. It also does not fit with the regularity of the fault which seems to be a time period. An engine could be at any temperature at start and therefore it would take longer to get to a certain temp.
I can't see how the lambda is used during cold start as it needs to get up to a certain temp to start switching. More fuel is being chucked in from the enrichment which I guess is also coolant temp controled as one variable. So either something is ending after a certain period or the ecu ignores certain parameters and has a set routine a bit like limp home it runs until it looks for the signals it needs to run. I believe limp home is N alpha so even if we run the engine in that mode by say disconnecting the maf, I am not sure what that would tell us.
So without that bit of knowledge about the transition from start, I am not sure what to suggest next. It does seem that its not a unique fault. Others have had it one day and not the next which means there is no definitive solution. Pretty frustrating!

[twoqu]

http://www.sjmautotechnik.com/troubl...ing/20vo2.html

If the info in the above is accurate then the cycling is consistant with the symptoms. But why would a new lambda behave in a way that was inconsistant with the ecu unless there is some incompatability. It's a possability I guess.

[twoqu]

The N80 is also a suspect. It also appears to be activated after lambda control is initiated. It is also cycled. So the mixture is to a certain extent part inj and part vapours.
Without power it is open. If it fails the engine can also suck in the vapours via a non return valve during high vac conditions.
I know there is no codes but clearly if the engine is injesting the fuel vapours constantly that might reek havoc with the mixture

[k.alle]

The N80 is also a suspect. It also appears to be activated after lambda control is initiated. It is also cycled. So the mixture is to a certain extent part inj and part vapours.
Without power it is open. If it fails the engine can also suck in the vapours via a non return valve during high vac conditions.
I know there is no codes but clearly if the engine is injesting the fuel vapours constantly that might reek havoc with the mixture

Should not this scenario make the pulse witdh shorter?
If 1-1.3 ms is a baseline for normal idle and fuel vapors comes in uncontrolled I would have thougth the injector time would decrease.
Or is it because it essentialy becomes an air leak in that case?
The oxygen introduced from the tank increases the injector time?
Sorry for rambling but it is a interesting topic to me.

[EDIT]
I guess one way to test would be to plug the hose to the tank behind the N80.

[twoqu]

I guess if we knew whether it was running lean or rich then it might be easy to point the finger. It does seem that the N80 would cause a lower load and shorter injector time. We have only seen the opposite! I was only trying to find things that cycled and only operated at a certain stage and were possibily implicated in fueling! The other possibility of course is that the engine is being starved of air and that would point to some leak!

I also think I misread that temperature of Lambda closed loop! The time period might be more related as to when the ecu detects the lambda switching although we still need an explanation as to why that might cause the issue!

[twoqu]

https://www.s2forum.com/forum/techni...tle-in-neutral

Thats interesting. I doubt whether the gauge is particularly accurate although from your screen shot of VCDS is looks as though you are at 13V! Perhaps we are overlooking something basic such as an electrical issue or ground especially as the car has just recently been put back together. Just a thought.
Do you have an earthing strap from the alternator bracket like in the third pic here:
https://www.s2forum.com/forum/techni...46#post2050546

[s0_big]

https://www.s2forum.com/forum/techni...tle-in-neutral

Thats interesting. I doubt whether the gauge is particularly accurate although from your screen shot of VCDS is looks as though you are at 13V! Perhaps we are overlooking something basic such as an electrical issue or ground especially as the car has just recently been put back together. Just a thought.
Do you have an earthing strap from the alternator bracket like in the third pic here:
https://www.s2forum.com/forum/techni...46#post2050546

The voltage jumps around bit, but between 13-14 V. I dont have the extra earth cable, just the 2 wires on the back side of the generator. I got hold of a set of used fuelinjectors so i will try them some day soon.

[twoqu]

Surely the engine should be earthed to the chassis. The generator wire are bat + and lamp warning!
Quick test would be to use a jumper lead between the engine and the chassis just to see if it makes an improvement. If it does you need to research the issue further. The parts catalogue does show an earth cable but does not show its location. At a steady speed I can't see why the voltage would fluctuate that much.

[twoqu]

Can't speak for RS2 but:
https://www.s2forum.com/forum/techni...88#post1339188

Perhaps that owner added an additional one. Guess the car doesen't know where its fitted. I noticed it before on that but wasn't certain about its function.
Anyway, you should have one somewhere!

[quattrito]

I had and earth cable on my 3B at the exact same location as the one in the topic above.

[twoqu]

Of course the voltage fluctuation could also be a symptom of the engine cycling! It's hard to untangle the two issues. Are the reading out of whack the issue or just because the issue is occuring.