High Tick over until stationary

[franksand999]

Hi, I have a 1997 Polo 999cc Petrol.
When the car is warm the tick over is high (about 2000rpm) - when the car is freewheeling, when I brake and become stationary the tick over reduces after a few seconds to what I assume is the correct tick over (900rpm ?).
I sprayed some carbi cleaner into the carb, but the tick over has increased (up from 1500 to 2000rpm).

I dont have any diagnostics software, just tools, will I be able to resolve this problem, can I assume its just dirt in the Throttle body, and the Lambda sensor needs a clean (although both these most commonly seem to reduce idle tick over - frmo what I've read.)
I've also read about the MAF (airflow meter) and Temperature sensors possibly being faulty and affecting tick over, I have an electrical meter, but dont know what values to test for.

Lastly, I've also read I will need diagnostics software to reset the 'throttle alignment', should I get this software before taking the throttle body apart, as I dont want to disassemble something I can put back together.
Many Thanks F

[towcestervag]

throttle valve will need to be reset in base settings if you have cleaned it

[franksand999]

Thanks for your reply, but do I need Diagnostics Software to 'reset base settings' ?
Thanks F

[towcestervag]

you will need diag machine capable of resetting are you local to me Towcester Northants?

[franksand999]

I am in NW London, so a quick nip up the M1 I suppose.
One thing thats odd, it uses loads of oil if I do a motorway run and drive it hard - say 80mph, in town it doesn't use a drop.

[towcestervag]

few things poss 1, breather pod at back off engine partially blocked look for oil in air cleaner
2, valve stem seals worn look for oil smoke on decelleration
3,oil leaks?
4,worn rings?

[franksand999]

Ok, thanks I'll have a look at this 'pod' breather - I did notice a build up of oil in the air filter cover (but wouldn't say it was saturated) when I first had a look around.
Will also check for smoke on deceleration

I've had a look underneath and round the engine and cant really see where an excessive amount of oil could be leaking from.
On my last run, up the M1 I had to do a full top up of oil (ie it had gone from full to empty) after just a few hours motoring at 80 MPH.
Just cant see where all that oil went, guess I should get someone to follow me at 80MPH, see what comes out the exhaust.

[franksand999]

OK, I've looked at the breather and it was all gunged up with Mayonaise, mostly in the inlet to the air filter box by the rubber 'one way' washer, I couldn't pull the pipe off from under the inlet manifold, so I've cleaned it out as best I could and made sure its breathing OK.
Its made an improvement a little, car idles at about 1600rpm rather than the 2000, but it still idles at 1600 when free running out of gear down hill, only coming to 900rpm when finally stationary.
I've now acquired a ODB2 cable and some VAG-COM software, do I need to reset anything ?
Should I do any further cleaning, I cant see what the POD breather connects too, I can feel round the back with my hand, but its just too cramped to doanything else without having to remove large parts of the inlet, which I'll do if necessary.
Thanks F

[stonedagain]

OK, I've looked at the breather and it was all gunged up with Mayonaise, mostly in the inlet to the air filter box by the rubber 'one way' washer, I couldn't pull the pipe off from under the inlet manifold, so I've cleaned it out as best I could and made sure its breathing OK.
Its made an improvement a little, car idles at about 1600rpm rather than the 2000, but it still idles at 1600 when free running out of gear down hill, only coming to 900rpm when finally stationary.
I've now acquired a ODB2 cable and some VAG-COM software, do I need to reset anything ?
Should I do any further cleaning, I cant see what the POD breather connects too, I can feel round the back with my hand, but its just too cramped to doanything else without having to remove large parts of the inlet, which I'll do if necessary.
Thanks F
The higher idle speed whilst coasting my be design intent. I worked on Nissans & they did the same - it is to prevent stalling, which would cause loss of power steering, loss of brake servo vacuum, etc.

[franksand999]

Its still using oil sporadically - and a whole dips sticks worth on a long journey, no smoke is visible from the exhaust.

I have now bought a cheap cable off ebay and used a demo version 409.1 of VAG COM to list faults, its telling me the Oxygen Sensor (assume Lambda sensor) (039) is faulty (NO SIGNAL).
I will clean/replace and see what happens, I assume some Engine Management Values will need to be reset.
I also need to clean the POD Breather further - but to do that it looks like I must take off the inlet manifold, if I also clean and fiddle with the Throttle Body I need to do a TBA (throttle body alignment) - as I cant reset basic values using the VAG demo software, can I simply disconnect the battery for several hours and hope it does a reset that way ??

If I dont fiddle/clean the Throttle Body and take off the inlet manifold with the throttle body attached as one lump, do I still need to do a TBA Basic Settings reset.

Is there any shareware I can download that will simply allow me to reset Basic Values for the TBA.

Thanks F

[franksand999]

I've found out that if even disconnecting the battery, you will still need to do a TBA using VAG-COM or similair if you fiddle, the software cycles through some tests to realign what ever it needs to, and will reset using certain values measured during these tests, which I will now be able to do once I've cleaned the throttle body (and after cleaning the POD breather).

If I replace/clean the Lambda sensor do I need to reset anything using the VAG COM software.

Thanks F

[franksand999]

I've discovered there is an Oil Separator Unit - under the air inlet manifold, which is part of the crankcase emission system, a black plastic box (Cost £50) from VW main dealer spares, i've had it off and cleaned it (I assume its just a wire gauze trap - and only needs cleaning - not replacing). It was all gunged up with Mayo and black sticky deposits.
I've also had the Throttle body off and given that a clean with carbi cleaner, there were some deposits around the butterfly.

I've put it all back, done a TBA - but the problems still there, in fact the idle at motion is now bit higher (as it was before 1900rpm).

Re: the Lambda error - I cleared the fault codes and did another Autoscan, but its not finding any faults this time, so maybe it was just an error generated when I've worked on the car previously.
Would you recommend replacing the Lambda Sensor (G39) anyway - as the cars done 85k, assuming 30-50k usable life - if its been done once - its up for another now ?

I'm going to look at the various other breather and vent tubes and valves in the engine compartment to see if these are blocked up/not working.

Thanks F

[franksand999]

Checked all the pipes - and these all look fine.

Took it for a run and its still losing oil :(I will take the Oil separator off again and give it a soak overnight. I will also run some Wynns Oil Flush through the engine.

I discovered an Earth Tag that goes to the throttle body was bolted on between the inlet manifold and the throttle body - possibly letting in air, I've removed it and put it where it should be (on top of the throttle body), engine idles perfectly when stationary (as it did before) - but still idles at 2000rpm when moving, when you come to a stand still revs slowly drop and stabilise to 800 rpm (or there abouts).

I disconnected the 'Vehicle Speed Sensor' (on the transmission) and the problem went away - ie I could free wheel out of gear downhill without idle revs running at 2000rpm (or there abouts).

Any thoughts appreciated.