VW Polo Engine Rev Issues

snappieT

Hi all.
1999 Polo, recently serviced and passed NCT. Not being driven often (only once a week for a couple of hours).

When idle, the engine seems to keep almost cutting out, and the tachometer needle bounces up and down. Normally, it would idle at about 700-800rpm, but every few seconds it'll drop down to 500, the engine will rev itself a bit, and it'll come back up to 800.

If you try to take off when this is happening, it's hard not to cut out - you really have to give it more throttle to compensate.

I'm trying to figure out what this could possibly be. It didn't happen for a few weeks after the service NCT, and seemed to only start after the last fill-up of petrol, could it be less-than-perfect petrol causing the problem? The cold/damp weather combined with not being driven often? It is being parked on a kerb, could all the muck in the petrol tank be making it's way to one side and be getting sucked into the engine? Or is it something more serious that needs a check.

It's never actually cut itself out, and no warning lights come on, but it is noisy when it drops down to 500 etc.

Thanks,
S

kildarelad

Could be dirty carbs on the carburettor ive seen it alot with the polos.Get carb cleaner and try it

ianobrien

kildarelad wrote: »

Could be dirty carbs on the carburettor ive seen it alot with the polos.Get carb cleaner and try it

The Polo has fuel injection - had since 1990/1992 era. No modern car has carbs, and a '99 Polo most definately does not!

OP - I can think of a few things (fuel filter, fuel contamination, coil starting to breakdown etc) but your best bet it to get it to a decent mechanic. Without seeing the car, it's hard to give an accurate diagnosis over the 'net

woody33

http://www.clubpolo.co.uk/forum/lofiversion/index.php/f4-0.html

Try a search here.

http://www.clubpolo.co.uk/forum/lofiversion/index.php/f4-0.html

snappieT

Thanks for the suggestions, may just have my mechanic look at it.
If it makes any difference in the diagnosis, I was showing someone the issue last night, and when I got out of the car, the road below the exhaust outlet was pretty wet (and it didn't smell like petrol).

kildarelad

The Polo has fuel injection - had since 1990/1992 era. No modern car has carbs, and a '99 Polo most definately does not!

OP - I can think of a few things (fuel filter, fuel contamination, coil starting to breakdown etc) but your best bet it to get it to a decent mechanic. Without seeing the car, it's hard to give an accurate diagnosis over the 'net

I meant the inlet manifold on the top of the engine when you lift off the airbox.Ive often had to spray carb cleaner into it when i had problems with polos revving up and down on idle

daveharnett

snappieT wrote: »

Hi all.
1999 Polo, recently serviced and passed NCT. Not being driven often (only once a week for a couple of hours).

Does it get driven for an hour or more in one session, and if so is the problem still present after? A lot of issues related to under-use can resolve themselves just by driving the car for a more extended session. Helps to get the battery charged, the oil and coolant moving properly, and the engine breathing normally.

Muckie

It seems that the air breather's have a habit of "gunk"
building up, recently cleaned out one of theses cars a 97 polo
Theres a pipe from the bottom of the engine that joins into
the air breather, cleaned it out and replaced the distribitor cap
and the car is running like a clock. Good luck.

kildarelad

It seems that the air breather's have a habit of "gunk"
building up, recently cleaned out one of theses cars a 97 polo
Theres a pipe from the bottom of the engine that joins into
the air breather, cleaned it out and replaced the distribitor cap
and the car is running like a clock. Good luck.

Your bang on there Muckie thats what i was on about

snappieT

daveharnett wrote: »

Does it get driven for an hour or more in one session, and if so is the problem still present after?

Each use would be about 3 hours in total, but 2 of those are someone learning to drive (cutting out lots, taking it very slow...)

Muckie wrote: »

It seems that the air breather's have a habit of "gunk" building up, recently cleaned out one of theses cars a 97 polo
Theres a pipe from the bottom of the engine that joins into
the air breather, cleaned it out and replaced the distribitor cap
and the car is running like a clock. Good luck.

I may have a look at that. Thanks.

el tel

Engine speed sensor might be fooked, the diagnostic shoud show this up. I'd reckon €100 to diagnose and repalce at an indy.

johndaman66

Experiencing the same problem as SnappyT but only when the car is cold and for the first five minutes or so...the time after which you would expect the choke to close in. Whenever clutch is pressed to change gear the battery light momentairly flashes but engine fires again when you go into gear...kind of like clutch starting a car. You need to keep the boot in after starting the car cold and idling. Eventually after 5 minutes or so it will tick over at about 500rpm and is still threatening to stall. When it get up to full operating temperature the engine will tick over at around 8-900rpm and smoothly enough for a polo.

Muckie the pipe you mention do you reckon this is the culpurit in my case perhaps? Also where abouts in the engine is it as was looking for it today and couldn't see it. Is it left or right hand side of engine bay as your looking into engine bay and is at back or front of engine? I can't for the life of me see it but perhaps I'm overlooking the blatantly obvious:). It does run from the airbox down? BTW car is 1996 polo 1043cc.

Muckie

Hi the pipe is on the left hand side, back of the engine going into the
the air breather housing from underneath, its about 1/2 inch thick.
It runs all the way down to the bottom of the engine, i've used a coat hanger, WD40 and an old rag to clean out this pipe that builds up
with fatty oil or "gunk".
Hope that helps if not let us know.

johndaman66

Many thanks for your speedy and helpful response Muckie. I will try to get a look at the next time I have a few minutes to spare with daylight (seldom enough these days!). Again I appreciate the assistance and will let all know how I get on.

AzureAuto

Common enough for the throttle plate to become clogged with gunk/sooty emissions, (depending on how the engine is running). This in turn causes the cars ECU to overcompensate for the decrease in oxygen by overfuellng, which increases the engine revs. This is picked up by the lambda sensor in the exhaust. Because this reading doesnt tally with the air mass readings from the air flow meter, the nett effect is a cycle of fluctuating engine revs nicknamed "hunting".
To cure it, give the throttle plate beneath the air filter a good clean with some carb spray and a toothbrush. Change air filter if it is dirty or due to be changed. Clean out all engine breather pipes, in partiular the PCV valve mounted at the back of the engine block; if its gunke up proper, they're cheap enough to buy and replace. This should sort the problem out.
Regards.

johndaman66

OK, went out this morning to start the Polo but it wouldn't. Well it did initially, ran for a few seconds at over 4,000rpm when I kept my foot to the floor let my foot out a wee bit, ran down to 3,000rpm and just cut out before I could get the revs up again. Tried starting it again, engine was turning over but would not fire up. Luckily brother was finished for Christmas so got the loan of his car for work for the day.

With some kind assistance this evening I managed to take off breather pipe (runs from bottom of air filter housing to about half way down engine, not sure what it joins into). There was some gunk in the pipe but in fairness not a lot. Ran a few jugs of hot water through it and air from compresser and managed to get some gunk out. Reattached pipe and re-assembled everything. Still no joy though. Engine turning but won't fire up. Think I've almost flattened my battery at this stage probably. Something tells me it could be fuel pump/ fuel filter badly clogged. I know the same thing previously happened me in a Vectra and syptoms are somewhat similar. Mechanic tested fuel pump by spraying easy start into air intake, engine ran for a few seconds and then cut out again. Not a hope I'd get a mechanic now for the next week or so or until the silly season is over. Anybody have any further insight or pointers based on the symptoms of the Polo?

Help appreciated.

AzureAuto

without looking art it its hard to say wat the problem might be. perhaps the engine has been flooded with fuel from continuous cold starting. You could try removing the spark plugs and putting them in a moderate oven for a couple of minutes to clear off any fuel which might have collected. During this time the petrol from the cylinders should have evaporated. Whilst they are out, test the ignition system by grounding a spark plug attached to a HT lead on a suitable engine earth and turning the engine over. Look for a strong blue spark which indicates a healthy ignition system. Dont do this for prolonged periods of time.

mikeyboo

had the same problem with the gf car she was driven home and it stopped on the road? did you find a answer to your problem?