Unable to diagnose 1998 Polo "one day no power, unable to idle, VAG-COM has no codes"

Unable to diagnose 1998 Polo "one day no power, unable to idle, VAG-COM has no codes"

Hi to you all from a newbie in Australia

Got my shiny new VAG0COM to help me track down the problem that suddenly appeared in my Polo. I'm working through the VAG-COm capabilities but there is a LOT there, hope someone can point me in the right direction..

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History (1998 Polo 1.6 lkitre, auto, 6N1):
Car has 92K Kms on it, has never had a problem with running, power, starting, etc One day at startup, it had very little power, would not idle below 1100, barely moved on the road (like a dead cylinder perhaps, in the level of power reduction happening) and could go no more than ~5-10 kph, I had to select lower gears to get that too. Easily stalled out if I did not keep the revs up. I was able to move it to a place to work on it out the back of my place, but lots of stalling and nearly didn’t make a very minor hill, the power was so poor. In summary, one day with no warning (I have done my own diagnosis and repair work on many cars across every system (except transmissions) since the 70’s, I am very alert ti changes in engine function - so this was not a gradual slide into a problem, it just happened suddenly one day at startup. Very weird to be so hard to diagnose / correct....

What I've done:
Battery disconnected for a month while away. Returned and re-connected and ...
Started fine again. Runs well above ~1600rpm, it feels and sounds fine there and higher. This was what I had found myself left with before going away for a month.
If allowed to drop to 1000 rpm (taking foot off accelerator) - it hunts around across a range of a few hundred RPM, producing rough idle to smooth, engine lifts and drops rpm, gets rough, gets smooth, and so on. No obvious pattern to what is happening with the ups and downs though.
The car progressively seems to try to lower rpm by itself, this also brings increased roughness mostly. Like having one cylinder running very badly (but plugs show no issues). It then went to ~900 RPM and was rough then smooth (as if under ? ECU? control, was not consistent like if there was a vacuum leak). Then went a bit lower, hunted around again showing variously smooth then rough idling. Then a little lower and the same thing. Then after about 4 mins it dropped lower to about 500 rpm and stalled out.
But on scan with my new Ross Tech VAG-COM I get no codes at all, before or after trying things / running for a while. The battery is well charged and have tried all this after battery disconnect / reconnects, no effect.
Trying again today after being away, starts fine but drops to a very rough 600-700 rpm, sometimes up to 900, but variously rough then smooth idling. Keeps going for a few mins then dies as before.
If it was an old style carby I’d be thinking idling jets, but this is an electormechanical throttle control system.

What should I be looking at next? I’ve tried a few things, oith no change to the outcome...

Checked and cleaned the injectors (all fine)
Replaced the lambda sensor in the exhaust pipe
Spark plugs replaced (no differences in appearance to suggest cylinder issues)
Have cleaned the existing throttle body.
Tried another throttle body (wreckers).
Tried another ECU (wreckers).
Have not replaced fuel filter as that does make sense - it runs well at high rpm (i.e high fuel flow).
Tried throttle adaptation as per the Ross Tech wiki/ website video (both 001 and 098 codes, and 001 is not the adaptation code on this model), it failed to do anything, and it shows weird and very high starting values for the throttle pots:
Address 01: Engine (032 906 030 S)
10:09:10 Group 098: Throttle Control Basic Setting
128.0 Throttle Pot G69 Voltage 0.500...5.00V
119.0 Throttle Pot G88 Voltage 0.500...5.00V
53.0 Operating Mode
25.0 Adaptation Status Idle/OK/ERROR

Nothing tried with the VAG-COM with the engine “running” :-)

So, in the absence of any VAG-COm codes coming up, and the Adaptation not working, I’m a bit lost. It definitely seems like it is a throttle reset /adaptation issue not being resolved ATM, but I am new to this area.

What might the the high 098 Throttle Pot values mean for me? Any suggestions for next steps?

Thanks,

David Parsons
Adelaide, Sth Australia

Hi and welcome. It might be helpful if you'd post a scan even if there are no fault codes. The scan will show people exactly what ECU you've got.

-Uwe-

Thanks Uwe, will do.

Here is the full autoscan for the Polo, hope it can assist anyone with ideas on what's going on here
Thanks in advance for any input...
Cheers
David

Whats the intake vacuum level when it does idles badly.

Also is it Fly by wire or cable throttle?

1998 is almost certainly still a cable throttle.

It might be worth trying Basic Settings in Group 001 on this ECU. Coolant temperature should be at least 80°C when doing that.


-Uwe-

Uwe, Ran at > 2000 rpm for coolant temp over 80C.
Tried 001 and (immediately) no effect on "GO".
Also 098 again, no effect.
Found a ref to vacuum being block 204, tried that but it's the default 'nothing there" standard set of numbers that comes up.

I have spent 10 mins trying to upload screen-shot images of the VCDS screens for things I tried so the details / numbers are there, but can't work it out, seems only an image with a URL can be uploaded. I have a word doc, or jpg's, with the screen info - am I missing something simple here for pasting images into these windows?
Cheers
David

platydog2 said:

I have spent 10 mins trying to upload screen-shot images of the VCDS screens for things I tried so the details / numbers are there, but can't work it out, seems only an image with a URL can be uploaded. I have a word doc, or jpg's, with the screen info - am I missing something simple here for pasting images into these windows?

Click to expand...

Yes, we don't allow image uploads here. Please see How to Post Pictures.

-Uwe-

Thanks, did not see that limitation, and has always wandered what imgur was :-)
Here's the images:
https://imgur.com/zVdmx4R


and
https://imgur.com/O1wwsuB


Hope this posting works
David

platydog2 said:

Hope this posting works

Click to expand...

I fixed it for you. Click "Edit Post" to the above post to see what I did. In order for IMG tags to work, you must link to an actual image file, generally something that ends in .jpg or .png.

-Uwe-

I see there have been 179 views of this but no posts with few suggestions on my problem - is this a "crowd-funded" indication that I have a too-hard problem, or do I need to re-post / move the questions into (say) the Car Repair section to redirect/rejuvenate it ?
Cheers
David

I guess a lot of viewers are not familiar with such old-school engine and TB. Personally I hate Magneti Marelli ECU's and other car electrics/electronics parts. Sometimes those use to have unpredictable behavior
It's hard to give some reasonable advice without being next to car, without touching it, hearing, feeling how engine runs... Some advices:
- are You sure another used TB You tested was OK?
- have You checked for intake and EVAP leaks?
- how HOS signal look if plotted with VCScope?
- how ECT signal look if plotted with VCScope?
- try basic setting at group 000
- is accelerator cable checked for sufficient free play at TB (cable must have couple mm free play. Tight, without free play, is wrong).

I'll happily move this to Car Repair for you, but the reality is that when the car reports no faults, it's difficult to diagnose problems over the internet.

-Uwe-

Hi all out there ...
Is this a too-hard set of issues I have posted?
Any wild and crazy things out there I maybe should think about / check?
Cheers
David

Hi David,
As Uwe said, without a DTC it is hard to focus on any area, so you need to log whatever data you can, to diagnose what is happening. In addition you may need to manually check things with gauges such as fuel pressure, manifold pressure and scoping sensors.
Regards HMC

Hi David
Looks like there is no tip working?
I would force a fault entry by disconnecting the cable for throttle body while ignition on.
Then looking for the new entries, because of the Basic Settings error there must be an adaption fault entry.
Reconnect the TB and let the engine idle for a while.
Delete the faults and try basic settings again.
If that did not work, please perform a MVB channel map to show it here.
But anyway I think it is time to mount a good throttle body

http://www.volkspage.net/technik/ssp/ssp/SSP_168.PDF


What is status of EGT in exhaust?

or

036-906-051 G71/42 MAP sensor for aforementioned performance issues?

Additionally when doing a TV attempt of adaption, please be sure cable is not too tight and that the TV can move backward 5 MM and before commencing forward to count stepper angle.
If in doubt for cable tension or offset, remove cable to see if TV adapts with no cable installed, if it does reinstall and follow RTFB.

The TV must be clean and lubricated with light lube to float free!

Thanks to all the replies after my last question - I have inadvertently missed them as they were on the second page. How dumb can I be (and I will need to check why I am not getting notified)..

Before I go play, I tried a restart today after the battery was disconnected for several weeks while I was away.

Simply let it run, and with the VAGCOm graph function found that the sudden dropping and return of the rpm was about every 15 secs. That went on pretty steadily for 10 mins, with a small gradual mean reduction in rpm over that time (? while coolant temp increased perhaps). At the end I tried to move the car and drive it around a bit, but the effect of shifting into a laod situation (Rev or Drive) dropped the rpm so far that I had to pump to keep revs up, and even then the power (?) was so low it stalled soon after trying to drive a few meters. Maybe the regularity of the rpm drops gives a clue here?

I want to paste in / upload the CSV - it had rpm, ECU volts, TB position and TB voltages, but I have not been able to find an upload method, and no stickys that describe all, the ins and outs of uploads - can anyone point me to that info?

Many thanks for all the recent suggestions too!

David

Thanks to all the replies after my last question - I have inadvertently missed them as they were on the second page. How dumb can I be (and I will need to check why I am not getting notified)..

Before I go play, I tried a restart today after the battery was disconnected for several weeks while I was away.

Simply let it run, and with the VAGCOm graph function found that the sudden dropping and return of the rpm was about every 15 secs. That went on pretty steadily for 10 mins, with a small gradual mean reduction in rpm over that time (? while coolant temp increased perhaps). At the end I tried to move the car and drive it around a bit, but the effect of shifting into a laod situation (Rev or Drive) dropped the rpm so far that I had to pump to keep revs up, and even then the power (?) was so low it stalled soon after trying to drive a few meters. Maybe the regularity of the rpm drops gives a clue here?

I want to paste in / upload the CSV - it had rpm, ECU volts, TB position and TB voltages, but I have not been able to find an upload method, and no stickys that describe all, the ins and outs of uploads - can anyone point me to that info?

Many thanks for all the recent suggestions too!

David

Click to expand...

What is status of exhaust or intake for possible restrictions for FOD?

Thankyou for your suggestions Wolfgang., I will try them out.
But in your second line, I do not know what the 'tip' is, can you explain please?