2002 Polo 1.4 16v 100bhp - "Excessive EGR Flow" Symptoms

[seventh-heaven]

As per yesterdays post about Vacuum Pipes - I am looking at a friends Polo which is not running well and has an EGR Excessive Flow fault recorded.

Bit of background - the car has done 92000 miles and is in generally good condition although it is clear that the current owner has taken it for granted and neglected it for the 2/3 years of her ownership - maintenance is done on failure only! She has been complaining that in the last 6 months a number of issues have occurred which have led to it being unreliable including:

- poor starting from cold
- Engine fault light (download shows to be 16786 - EGR System P0402-35-00 Excessive Flow)
- occasional breakdown when engine stops but then starts a bit later
- started to need regular top ups of engine oil

I have removed the EGR valve and it is sticking and not functioning properly, but it appears to be sticking closed not open. The pipe from the EGR valve to the throttle body looks newer than the rest of the engine bay kit, but once out the carbon in it whilst not excessive shows it has been there a while. Had all the plugs out to do a compression test and they all seem high at around 170-180psi. Now it could be the gauge but I used same gauge on another engine within last 3 months and got more realistic readings. Plugs were very worn and so replaced and now it appears to start much better from cold so that symptom is probably a red herring in respect of the the EGR symptom. I reassembled the EGR valve and pipe with a cardboard gasket to block it off. Sure enough when I go out for a test drive I can get the EGR Excessive Flow fault to reappear - so I now that this is an incorrect diagnosis on the basis there was no flow through the EGR! Now I have never driven this car before (and used to driving a A6 3.0 TDi!) but none the less it felt a bit flat for 100hp. It would rev to the red line ok but not at the pace I expected.

So the question is what else could it be. My thinking currently is as follows:

- leak on EGR pipe where it goes into the Throttle body. O ring is there but could be leaking;
- Blocked cat causing excessive back pressure in the exhaust hence causing high compressions and poor air flow through the cylinder - If the flow through the cylinder is restricted then for a specific engine speed and throttle opening the manifold pressure will be higher than the ECU would expect leading it to think that the flow from the EGR is causing it.
- Worn exhaust cam again restricting flow but I would not expect it to be so consistent across all 4 pots;
- air leak in the manifold of vac system - one is not obvious but difficult to be sure. I suppose a Vac gauge could be used to draw a vacuum in the inlet and see if it leaks away. However this would not explain the high compression readings.

Any other suggestions or suggestions of how to check the above easily would be appreciated.

Thanks

[towcestervag]

you need a vagcom to check properly!
the egr valve will need to be reset in basic settings/readiness
have you cleaned out the throttle body?

[seventh-heaven]

I have a VAGCOM! That is where I got the fault code from. Did you really read my post or just the title?

The EGR valve will only need resetting if I replace it and the throttle body does not really need to be cleaned out it is satisfactory as it is! However I would appreciate any insights you have on the symptoms and issues that I described!

Thanks

[towcestervag]

have you checked the operation in output tests if it can be done on the polo?
you will need to check the wiring if you need a diagram let me know car details and will print you one off

[seventh-heaven]

Yes I have checked the operation of the EGR on the output tests and that is how I have worked out that it is sticking. It opens and closes normally and then occasionally sticks closed and needs a good tap to free it up again.

As I described in my post - I have all but eliminated the EGR valve as being the source of the "excessive flow" as I blanked it off with a solid gasket as a temporary measure and the fault light still returned.

[towcestervag]

the egr valve will still give you a fault reading as it has a potentiometer in the valve itself so whatever the valve does it will give a feed back to the ecu
change the valve mate

[metalmicky10]

just a small point,cardboard gasket(hot exhaust gasses),use a steel shim gasket,you might find your card gasket has burnt through.i did this job on a chaps car close to me, after cleaning the egr and throttle body.then a good blast up the motorway to get the rest of the cobwebs out of the engine,these engines need a regular good run to keep things sweet (no good as a shopping car) unless a good run is included in the cycle.
happy motoring

Just another small point,these 16valve engines will probably need valve stem seals at arround your mileage even more so if oil changes have been neglected.

[seventh-heaven]

Thanks for the note. Cardboard gasket was fine - I have taken it out again.

Noted re valve stem seals - are they a known problem on this engine? Presumably head off job!

Thanks

[metalmicky10]

Not sure if my last post went so here it is again,i think 16 valve in general and with the head on (compressed air down the plug hole)worth a comression check to check rings or boreware,also a can of wynns stop leaks to help soften the seals.lack of oil changes tends to harden seals,lots of carbon in old oil.
cheers,mick.

[seventh-heaven]

Done compressions as referred to in original post - appear high to me at 170 to 180psi