Hi all, new guy here with quite an annoying problem with my polo. First off it's a 2001 Polo 1.0 mpi 5-speed. I start it, and it will idle fine for a few mins, then after driving about a minute or two, it will start to bog down and have no power whatsoever, sounding like its running on 3 clyinders and backfiring through the intake, resulting in me having to stop, restart the engine and somehow that makes it so I can start off again, only to have the same problem recur, especially once I slow down to a stop. Now the car has been great up until a few weeks ago, with the very occasional "flat spot" when driving. But now it's terrible and basically undriveable. I have replaced the vacuum line going from the brake booster because it was cracked, and I noticed the small black check valve looking piece it goes into has a nipple broken off and is sucking air, but I don't think that would cause it to run the way it is. When I take the vacuum line from the brake booster off after the engine is shut off, it still has a decent amount of vacuum still in the line, not sure if possible bad brake booster? I'm really at a loss it's my first VW. Someone told me maybe EGR valve but I also can't find that for the life of me. ANY help would be appreciated as it's my daily.

First Welcome to the forum.

There should be NO air leak on that check valve! 1, it will reduce the brake servo efficiency & 2, it will be causing an unmetered air leak into the intake so causing running problems!! so get that fixed first, then get it onto VCDS/Vagcom to see if there are any fault codes stored (not all faults will put on the warning light)

First Welcome to the forum.

There should be NO air leak on that check valve! 1, it will reduce the brake servo efficiency & 2, it will be causing an unmetered air leak into the intake so causing running problems!! so get that fixed first, then get it onto VCDS/Vagcom to see if there are any fault codes stored (not all faults will put on the warning light)

Alright, I figured I should get that sorted lol. But would you have a link where I could find just the check valve? I've searched on ebay, euro car parts, halfords etc but nothing comes up..

Here is the video of what's happening, figured it was easier showing than saying. I epoxied the hole in the check valve but that didn't do anything whatsoever

https://www.youtube.com/watch?v=uGBybv-va-k

The check valve isn't listed as a separate part, only with the complete vacuum hose. Get it onto VCDS and see if there are any fault codes and take the fault finding from there

I've ordered a set of spark plugs and leads along with a spare coil from a friends parts polo, just to tick those things off the list, and the ones on the car are the original ones from 2001 too...so wouldn't hurt to replace them

I should add I started it again, and once it started idling rough like in the video I held the gas pedal down a bit to 3 grand, then slowly backed off till with my foot on the pedal, it was at 1000 and running fine. But as soon as I took my foot away, right back to bad idle till it died. Not 100% sure what that means

Have you cleaned the throttle body? air filter box off, can of carb cleaner spray and an old toothbrush, give it a good clean above & bellow the butterfly flap, and while your in that area have good close inspection of all the rubber pipes coming from the throttle body and inlet manifold

Have you cleaned the throttle body? air filter box off, can of carb cleaner spray and an old toothbrush, give it a good clean above & bellow the butterfly flap, and while your in that area have good close inspection of all the rubber pipes coming from the throttle body and inlet manifold

Yes I have, it was quite dirty. Also weird, but I undid the battery for a few mins, and hooked it back up and it ran "almost" perfect. I drove it around the block and it only had a few minor flat spots, but I'll bet the problem will come back as it just wiped the ecu.

Disconnecting the battery doesn't wipe the ECU on your model it's just a myth!! That only works on the very early models

It might pay to give the MAP sensor (drivers side end of the inlet manifold, two torx screws, don't loose the "O" ring) a spray clean with the carb cleaner, as they do tend to get gummed up with oil/petrol deposits and will give poor throttle response

Disconnecting the battery doesn't wipe the ECU on your model it's just a myth!! That only works on the very early models

It might pay to give the MAP sensor (drivers side end of the inlet manifold, two torx screws, don't loose the "O" ring) a spray clean with the carb cleaner, as they do tend to get gummed up with oil/petrol deposits and will give poor throttle response

Yup I just ran out and gave that a quick clean as well, it was wet with oil so I see what you mean. Also the little center part was off center and against the side, I pushed it back so it was centered in the housing part with gloves on. Put it back in and started it up, idling normal as of now, I'll have to give an update after I drive it to work tomorrow...

Well it drove most fine to work today, still has a low/hunting idle though, but driveable

Well the problem is slowly coming back again. No power taking off/dead spots when driving. Getting annoyed as I love the car but hate these gremlins it has. Could it possibly be the lambda/oxygen sensor? When taking off it has absolutely no power and sounds like it has small backfires coming from the intake when I floor it, then it doesn't clear up until about 3 grand then accelerates fine after 3 grand.

Edited 12 June, 201412 yr by z3chyd

Ordered a new lambda sensor. I changed the spark plugs/leads with no difference, but they were due for a change anyway. Really hoping it's the lambda sensor. No one around here has the vagcom reader stuff any I'm not paying the crazy price for one

For the cost of the sensor you could of bought a VCDS lead and found out if there were any stored codes!! changing items in the hope of a cure will cost more in the long run!

I actually just bought a VAG scanner and it should be here on either Monday/Tuesday, it was £20 so not breaking the bank like I thought a scanner would

The scanner I got is U281 VAG vw memo scanner and the reviews seem to be all good for it so I can't wait till it arrives to have a go with it lol

Still running like crap. Replaced lambda sensor and ran the codes, came up with upstream lambda sensor faulty(hence I replaced) and map sensor reading incorrectly or something like that so I cleaned it. Also temp sensor faulty as well. So I guess temp sensor is possibly the culprit now? I'm about done putting money into this car

So which of the lambda sensors have you replaced? and the MAP sensor you said you cleaned that in post # 11? with VCDS you would be able to see the actual output of these sensors and see if they are working correctly.

Buy genuine VW sensors when you can - you can be led 'up the garden path' with some of the others and they tend not to be as reliable.

Regards

Hi guys,

Sorry post here but i´m having exacly the same problem as the video "https://www.youtube.com/watch?v=uGBybv-va-k".

One thing i notice is also the car is working on 3 cylinders on low revs but if i rev it to 4k it back to 4, once the revs came down its on 3 again.
If i insist until the car is normal working temp (90º) it works fine on 4 cylinders doesn´t stall.

I already did since its was time to do it:
new timing + water pump + tensioner
new thermostat
new oil + filter change
coolant flush
spark plug coil
air filter
cabin filter
petrol filter

After all this it still does it, what can it be?
please help,
thanks

Is it showing an engine light on the dashboard? Have you scanned it for fault codes?

Unplug the air flow meter and see what it does.

Take the spark plugs out and see how they compare to this

https://ngksparkplugs.com/en/resources/read-spark-plug