Intermittent fault codes and idle issues - VR6

[_Matt_ 26]

Hi all,

I'm trying to get the car ready for Cosford 35th but am getting intermiitent fault codes on VCDS lite. I first had the blue ecu sensor which I replaced, now I get the MAF (early 5 pin on this car), clear it off and then I get the Lambda etc and the cycle continues. My thinking is that not all these sensors are at fault and perhaps I have an earthing issue affecting the whole system?

VCDS also can't connect to the ABS controller but I don't have the ABS light on (it comes on and goes off as normal on start up).

I've also lost my oil readout on the dash too, that connector looks particular green though and needs a clean up.

Symptons when fault codes appear - wants to stall but doesn't i.e coming up to junctions or reving from idle, idle will drop to 500rpm if stationery. Clear the codes and it all goes back to normal! 

Any ideas? Also lost stage 1 fan but am awaiting on a new sensor to see if that fixes it. Stage 2 works. I'm trying to avoid replacing sensors for the sake of it. 

Also have tried unplugging MAF and car stalls straight away - i remember doing similar analysis on my old car and it used to still run with MAF disconnected. If i disconnect the Throttle position sensor  with MAF connected the idle rises to 1000rpm and it runs fine.

Oh also i've checked the vacuum lines visually, all good, including the two green bungs under the waterpump area. I have cleaned out and bench tested the ISV. Cleaned out the throttle body at the same time. Inspected the intake boot and swapped with a spare too.  

Car is going to Stealth end of August for chains and clutch but would be nice to solve before. The car is is all original and not messed with in anyway but hasn't been used much at all since 2005, perhaps 500 miles a year since then. Still has VW coil pack too.

The car has always had these issues since buying it.

Cheers

 

[_Matt_ 26]

Battery new and always on trickle charge too + is charging fine off alternator (13.7-14.2v i see)

[Dox 22]

You should be able to view engine temp with vcds? Fluctuations would point to wiring / sensor faults

lambda plug is on the rear engine mount

you don’t mention whether issues hot / cold or both?

Edited June 14, 2023 by Dox

[_Matt_ 26]

Good point - hot, post 88 degrees coolant the issues appear now, though before the blue sensor was changed it was from cold too. 

Engine temp gets to 98 degrees before fans kick in which is what makes me think stage 1 is not happening as believe that should happen at c95 degrees off of the rad sensor. I had a read of the cooling guide on here and concluded it was probably the rad sensor. 

Readouts on VCDS are stable, lambda swings around 1 for example, idle is 680 when it's behaving. Throttle body angle seems reasonable.  

This is the car running normally, on warm up, no problems - it does have a miltek sports cat and miltek resonated exhaust as the only modifcation 

https://photos.app.goo.gl/qDvYGX2qaEKNQjWi6

This is it a few mins later after a fault code appears, shame i didn't capture vcds screen. Can do it again if helpful to see

https://photos.app.goo.gl/BEKYyUV6fDP6YEHf9

 

 

 

 

 

[Dox 22]

Sounds like popping in the exhaust? ie unburnt fuel and oxygen?

I'd pull ignition leads off with the engine running looking for the one that has least effect on the idle and investigate that cylinder, plug / lead / coil / compression

[Dox 22]

Lambda is ignored until engine hits a certain temp, hence swapping the CTS has lead to improved idle at low temp - original reading high?

[_Matt_ 26]

Cheers Dox will investigate. It does pop between 1-2k rpm on throttle blips, i thought it was the sports cat increasing the popping. My last one did as well but not as loud on the standard cat, when the Miltek was fitted.

Lambda of course could have been disturbed on wiring when the sports cat was fitted. The car probably needs a decent run but reluctant to do it at the moment. 

[_Matt_ 26]

OK some testing tonight, 2 issues at play I reckon - screenshots are the fans, that is when they come on - 98 degrees so probable stage 1 isn't working. Tomorrow I will switch out the rad fan switch as it arrived today.

I also swapped the coil pack and ignition leads over to a spare set - no changes and a touch worse actually on wanting to stall. The coil was a bosch unit on the car where as the replacement was a vw unit but made by some random company beginning with T.

I also noted when the issues occurred- about 80 degrees, so assume that is when the lambda sets in. No fault codes tonight, oh and I also cleaned up all of the earth points (under battery, to block, to starter and 3 under behind isv).

When the car wants to the stall the lambda reading drops as low as 0.83. It usually hovers close to 1 otherwise. Also it only wants to stall after giving it more than half throttle, if you rev it gently it doesn't do it.

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[_Matt_ 26]

Also cleaned the maf with a maf spray from liquid moly.

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[Dox 22]

If you swap a sensor you need to disconnect / reconnect the battery and drive the car several times to enable the ecu to relearn the new sensors parameters.

Is the throttle damper catching the throttle and closing it gently?

Are you reading the issue causing the stall or the ecus attempts at preventing a stall?

[_Matt_ 26]

I suppose I am reading the result of the ecu preventing a stall as the lambda reading was a second or so after the event.

Just tested the damper on the TB and is working OK and comparable to the other corrado I have here (it's going today supposedly).

So I need to take it out for a drive it seems then. I shall find some time to fit the rad fan sensor to try and get stage 1 working as believe that stage works solely off the rad sensor.

[Dox 22]

Disconnect the battery for a while before you restart from cold.

 

clear codes with vcds

 

use the car for a couple of days before tinkering.

 

ignition off if you disconnect anything, otherwise ghost codes will send you down dead ends / cloud the process.

[_Matt_ 26]

Cheers Dox, will disconnect now. Interesting re Ghost codes - perhaps that was the MAF intermittent I saw as I did disconnect whilst engine was running but hadn't done anyhting with the lambda, though that has not appeared and perhaps was a hang over from when the prior owner fitted the sports cat, but i had disconnected the battery in my ownership so maybe that is wishful thinking!

 

 

[fendervg 30]

This is how the ECU reset is meant to be done to get the learned values correct:

http://wiki.the-corrado.net/vr6_ecu_reset_procedure.html

Clearing the fault codes is just one part of the puzzle.

There was a lot of debate on if the whole procedure is needed every time, especially as it is quite time consuming and awkward, and that the car might just adapt eventually itself after a battery disconnect - some of the time a 10 minute wait with the battery disconnected seems to be enough.

The main thing is, after battery disconnection, the ECU and sensor beviour can't be relied on until the learned values have been adapted to.

It could also be worth taking a close look at your cam sensor/hall sender (either part of the dizzy, or to the right of the coil pack depending on year) - I've seen this cause intermittent cut-outs and stalling when faulty.

Hope this helps a bit.

 

[_Matt_ 26]

Cheers Fen, will have a read. Does point to car needing a drive really and reassess situ. 

I did the cam sensor on my last one, although I say stalling the car hasn't stalled yet, just acts as though it wants to.  

[_Matt_ 26]

So took the car out for a spanking and after an initial few want to stall moments early on in the journey it stopped doing it. The oil read out also came back too. Fans come on at 98 degrees still , i did install a new rad fan switch and also swapped over the fan control unti from my parts car. Perhaps reading too much data otherwise unknown to me with vcds constantly plugged in though I think fans came on at 96.6 when i came home - perhaps it just needs a good blast and get heat into it to burn stuff off in the engine bay. 

I'll take it out again tomorrow as you guys suggest just to get it moving.

I wasn't able to peform the basic adaption bit of the ECU guide as only have the free version of VCDS.

Fingers crossed anyway.. 

[fendervg 30]

When were you expecting fan stage 1 to come on?

I presume you have read this - it gives pretty much all the low down in the first few posts:

Switch On: 92-97 C (198-207 F)

Switch Off: 84-91 C (183-196 F)

So not too far off normal - you can also tell which speed it is by the noise of the fans - stage 1 is controlled directly from the rad sender, not the fan control unit - also remember that VCDS is taking it's reading off the blue coolant temp sender in the thermostat housing, so this may not be exactly the same as what the rad switch sees, which might explain the discrepancy. Either way there is no ECU or fan control module involvement in stage 1 - in fact the Motronic ECU has nothing at all to do with control of the fan, but monitors the engine temperature to switch from lean/rich map and engage lambda control after warm up.

The coolant temp gauge on the dash also uses a sender in the thermostat housing, so once again, possibly gives a different reading. If you can get hold of a spot infra thermometer, they are handy for confirming different readings around the engine bay.

Edited June 15, 2023 by fendervg

[_Matt_ 26]

Good point, my blue ecu is a new sensor so was relying on the reading against the vr6 cooling guide but yes the rad will be different and does explain the variance.

 

So it sounds like it is operating normally and I'm free for Cosford and hopefully safe in traffic.

 

I've never heard stage 2 before, but read stage 3 you'd know about. My fans sound the same as any other car when they come on.

 

If this is the case I'll leave this part and move on to the next job - top mounts, crunch and squeaky.

 

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[fendervg 30]

Yep, stage 1 is just like any other car, 2 is noticably loud and stage 3 is like a jet turbine taking off and will drain your battery flat in about 20 minutes - don't ask me how I know!

[_Matt_ 26]

Good to know - wrong assumption to make on mine then! I'll take it for a drive tomorrow and hopefully all will be normal with battery disconnect and relearn.

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[oneohtwo 8]

I've got a vague feeling that you need to adjust the com port speeds on you Laptop to get it to communicate with some modules, ABS might be one of them. I remember doing this to mine, although I can't find the guides now which isn't too helpful I know! But hopefully that might be a starting point. 

[_Matt_ 26]

3 hours ago, oneohtwo said:

I've got a vague feeling that you need to adjust the com port speeds on you Laptop to get it to communicate with some modules, ABS might be one of them. I remember doing this to mine, although I can't find the guides now which isn't too helpful I know! But hopefully that might be a starting point. 

Cheers will read up. I do get the light on occasionally now but all other issues with idle/stall are solved now with just giving it a good drive and using the revs.