Irratic Idling and Engine Cutting Out on the Mk4/5 Polo.

After owning a Mk4 16V Polo for 7yrs I found there was a few problems with the design of the car but the most annoying fault was that the engine would cut out when I came to a stop, usually when I dipped the clutch.

Now this is a VERY common problem so if your car suffers from this then don’t worry you are not alone.

My girlfriend has the same model Polo and her car cuts out in the exact same manner. After many many visits to the dealership when the car was in warranty they couldn’t find out what was wrong with it, they said they tried everything but I very much doubt it or else the problem would be solved.

As I got fed up of the VW dealerships I took matters into my own hands, I mean how hard could it be to investigate?!

Also another problem which relates to this problem is irratic idling, sometimes the engine would ‘hunt’ for rev’s, it would rev on its own from 1000rpm to 1500rpm and then back down to 1000rpm and then to 1500rpm etc. This is extremely annoying when you are in traffic and people are looking at you thinking you got a dodgy right foot.

Here are the things you can do to try and solve the problem of cutting out and irratic idling. These are the things I did on mine whenever it started to play up which was pretty much every 2-3 mths depending on how much I used the car.

The first thing you can do is to clean the throttle body, this part of the engine controls the amount of air going into the engine and is operated by the throttle pedal. As the oil breather is connected to the airbox the crankcase gases are being put back into the intake system and the throttle body gets very dirty with oil.

So to clean the throttle body please following the following steps.

Before doing this, go buy some carb cleaner spray from Halfords or any car accessories shop.

Step 1.

Remove the VW badge from the airbox, this just pulls off.

Step 2.

Disconnect the air feed to the airbox.

Step 3.

Remove the allen key bolt from inside the airbox.

Step 4.

Remove the allen key bolt from the front of the airbox.

Step 5.

Unhook the earth strap from the airbox.

Step 6.

The airbox can now be removed from the engine, pull the air box away from the engine, it might need a good hard tug if its not been taken off before as it is held down by a rubber gromet.

Step 7.

Once the air box has been removed you can now see the throttle body, now disconnect the electrical connector, the main car battery does not need to be disconnected but it can be done if you feel safer disconnecting it.

Step 8.

Remove the 4 allen key bolts holding down the throttle body.

Step 9.

Take the throttle body off the engine, might need a tug if its not been taken off for a while as there is a rubber seal.

Step 10.

Take off the throttle cable, it unclips from the plastic.

Step 11.

Now use the carb cleaner to clean the throttle body. Spray the carb cleaner into the throttle body and use a cloth to wipe the oil away. Open the butterfly and clean the edges of the butterfly. Basically what I am trying to say is give it a good cleaning!!!!! Once clean leave the throttle body to dry off.

Step 12.

Now you need to clean the inlet manifold, spray the carb cleaner into the inlet and use a cloth to clean the inlet, clean as far in as your hands will allow, there is no problem in using quite a lot of carb cleaner to do this as it will burn off in the engine when the engine is started.

Step 13.

Once both parts are cleaned it is now ready to be put all back together, to refit just repeat the above steps in reverse kinda thing!

Step 14.

Once you are happy that everything has been put back together properly it is now time to start the car. You might need to give it some throttle to start as the engine will not like the carb cleaner when it is cranked over. Once the car starts give it a little bit of throttle to clear the carb cleaner out of the engine.

Step 15.

The throttle body cleaning process is now complete!

Read on if the engine is ‘hunting’ ,ie, reving by itself.

If the engine is reving by itself ,ie, the engine is wandering then stop the engine if the engine is running, disconnect the main car battery, you might need to note down the security code for the stereo. Leave the battery disconnected for at least 3hrs, the longer the better, this will reset the ECU and should solve the problem of the irractic ilding.

If the idling is still irratic after cleaning the throttle body and disconnecting the battery it is now time to change the temperature sender on the engine. The temperature sender monitors the coolant temperature and feeds the information back to the ECU. This part could fail therefore give false readings.

Both parts can be bought from any VW dealership.

Replacing this part will require the coolant to be drained or if you wanted you could remove the old temp sender with the coolant in the engine (make sure the engine and coolant is COLD if you are going to do it this way) and put the new sender in straight away, some coolant will come out so make sure you are prepared for a spillage of coolant.

To remove the temp sender take off the electrical connector. Pull out the plastic retaining clip which holds the temp sender in, carefully pull out the temp sender, once removed put the new sender in along with the o-ring and put the plastic retaining clip back and connect the electrical connector back. Give the sender a tug to ensure that it is secured properly. Refill the coolant to the correct level.

Restart the car and the idling should have settled down, if not then disconnect the battery again for a few hours to ensure that the ECU is resetted.

I have had many years of doing the above steps to my car and my girlfriends car with success. The cleaning of the throttle body is the main thing to do, I do used to do this on a regular basis to stop the engine from cutting out. It did stop it for a while and then it would return so once again the throttle was cleaned.

I hope this guide solves any problems you may have with your Polo Mk4/5.

Disclaimer: All the above steps and suggestions are a simple guide. Please use this guide with care as ClubPolo and myself will not be resposible for any damage the above steps might cause to your car and engine.

hiho

the cutoff´s and the up an down reving on the Polo 6n1 16v (only this one) with the old AFH 16v comes from the ecu.

Quote from VW:

Motor geht aus I'm Schub - Wassertemperatur 40 - 80 °C

Sporadisches Motorausgehen beim Auskuppeln in Schubphase während des Wiedereintritts der Kraftstoffeinspritzung (Einschaltpunkt nach Schubabschaltung - Drehzahlbereich 1.400 - 1.200/min.) und hoher Generatorlast durch elektrische Verbraucher I'm Kühlmitteltemperaturbereich von 40 bis 80 °C.

Ursache

Abstimmung Motorsteuergerät.

Serien-Lösung

Keine Serie.

KD-Lösung

Bauen Sie das Motorsteuergerät - ET-Nr. 030 906 030 E - mit dem neuen Datenstand 3745 ein .

and:

Technische Problemlösung

Problembeschreibung

Sporadisch erhöhter Leerlauf bis ca. 1500/ min oder Motor sägt.

Ursache

Abstimmung Motorsteuergerät.

Serien-Lösung

Keine Serie.

KD-Lösung

Bauen Sie das Motorsteuergerät - ET-Nr. 030 906 030 E - mit dem neuen Datenstand 3745 ein.

= in english: the programm in the stock ecu ist wrong and it will produce an engine cut off while pushing the clutch and/or the idle speed from the engine would raise too ~1500RPM. Vw say´s chance the ecu too an newer one.

THANKS !!!! !

hiho

the cutoff´s and the up an down reving on the Polo 6n1 16v (only this one) with the old AFH 16v comes from the ecu.

Quote from VW:

Motor geht aus I'm Schub - Wassertemperatur 40 - 80 °C

Sporadisches Motorausgehen beim Auskuppeln in Schubphase während des Wiedereintritts der Kraftstoffeinspritzung (Einschaltpunkt nach Schubabschaltung - Drehzahlbereich 1.400 - 1.200/min.) und hoher Generatorlast durch elektrische Verbraucher I'm Kühlmitteltemperaturbereich von 40 bis 80 °C.

Ursache

Abstimmung Motorsteuergerät.

Serien-Lösung

Keine Serie.

KD-Lösung

Bauen Sie that's Motorsteuergerät - ET-Nr. 030 906 030 E - mit dem neuen Datenstand 3745 ein .

and:

Technische Problemlösung

Problembeschreibung

Sporadisch erhöhter Leerlauf bis ca. 1500/ min oder Motor sägt.

Ursache

Abstimmung Motorsteuergerät.

Serien-Lösung

Keine Serie.

KD-Lösung

Bauen Sie that's Motorsteuergerät - ET-Nr. 030 906 030 E - mit dem neuen Datenstand 3745 ein.

= in english: the programm in the stock ecu ist wrong and it will produce an engine cut off while pushing the clutch and/or the idle speed from the engine would raise too ~1500RPM. Vw say´s chance the ecu too an newer one.

So to solve this problem completely they are recommending buying a new ecu? but how much will that cost and exactly how effective and easy is the throttle body cleaning? My car tends to cut out when I'm changing down from second to first, basically when my foots on the clutch, but it does sometimes cut out when changing down at higher speeds as well, the revs just die. I've never experienced it reving on its own though. Its a Mk 4 1999 and its done nearly 80,000 miles now. Is this a common problem for its age?

Cheers

Thought I would correct this:

Disconnecting your battery WILL NOT do anything to your throttle body. The only way is perform basic settings through VAG-COM or VW Tools

I have the same cut out problem but mines an 8v do they have the same ecu/ throttle body?

same instructions to clean the throttle body on an 8v

same instructions to clean the throttle body on an 8v

i have done this.. (had zero effect!!!!)

will change the temp senders next.....

Right i recently had this problem and had to get the AA out to have a look at it and apparently he said that there is some sort of chip or sensor in the distributor that can go down and cause the cutting out and irratic idling that i was experiencing. Now because i couldn't find any 16v afh's in a scrappers nearby i decided to investigate. So i went on gsf's website for a distributor and found that it is the same distributor for most of hatchbacks as they were all the same part number. so i went to the scrappers and found a 1.4 8v in there and got one off that including the cap and rotor arm for 15 quid and it's working fine now. happy days!

by the way i'm not saying it will cure you are problems but it did mine so it's worth a try i say.

I've cleaned my throttle body and replaced the temp sensor...but is still not sorted!what do i do now?

any ideas?

please help

I also have a 1998 1.4 16v that is cutting out. I have cleaned the throttle body, changed the HT leads, dizzy cap and rota arm. I also changed the coil pack as it went pop.

It is still cutting out . This seems to be a common problem with no common fix.

ok... thats all well and good

but what if its happening on a 1.6 8v that runs off a carb.

Any thoughts anyone so far on mine i have had a new fuel pump, Sparks,leads and dizzie changed...

Is it worth giving some of the things that have been said by Robin a bash???

I'm a bit confused here, can removing the throttle body cause any problems or not? Or are the problems that people are discussing here unrelated to the throttle body cleaning? I'm a bit confused and unsure if I should take off my throttle body and clean it, or could that cause any problems that I couldn't solve?

Cleaned my throttle body (it was filthy and the carburetta clean spray i bought from Halfords worked a treat) and changed the temp sender (aprrox £12 from my local GSF) as directed above , fingers crossed but its running smoother than its done for years and its not stalled once or dropped below 900rpm once when applying the brake or dropping the clutch. and its been 5 days now since i did it

didnt need any reset on the ECU , but it did idle around the 1000rpm for about 100 miles as noted by another club member but it has now settled down to 900rpm

never done anything like this before to a car and must say how damn easy it was to do, all finished within 20 mins.

I can recommend doing the throttle body removal and clean if your car is cutting out at traffic lights , and whilst your doing the clean change that temp sender..

Edited 20 March, 200917 yr by walkies2000

Do you have a part number for the temp sender?

Do you have a part number for the temp sender?

my car is a 1997 mk4 1.4 cl

the temp sender was a 4 pin blue

just told the guy at the desk make and model of the car and also told him it was a 4 pin (number of connections as there is also a 2 pin for different model) and that the plastic part was blue, the repacement part is also called blue but its actually green,

if this doesnt help just google GSF and give them a ring

Edited 19 March, 200917 yr by walkies2000

i had this problem with my valver, cleaning the throttle body had no effect, i realised one of my ignition leads was abit loose, that was a temporary fix then the problem came back, i then replaced the timing belt tensioner and water pump after that it ran perfectly

Thanks for this mine was hunting followed your instructions, now sweet as a nut ..

cheers

just done this, took about half an hour

my car now runs perfect, really didn't think such a little job could make so much difference to my car

proper happy lad now

gonna give her a clean

I had this high idle problem on

my afh 16v, so I removed my inlet

manifold and throttle body, cleaned them

both maticulously and also removed and blanked off my EGR (exhaust gas recirculation). I made a blanking plate for the inlet and exhaust side, this was adding to the carbon build up and because it's only vacuum controlled I just blanked off the vac pipe to it. This made quite alot of difference to the running, it was alot smoother, but it still idle'd high. But I went out and did about 40 miles, most of it with a heavy foot and now it's absolutely spot on

I still have a starting problem though so any help with that would be spot on too. When I start it from cold it runs as if it's missing for like 30 seconds and I can't touch the throttle for about 2 mins else it tries to cut out, as if there's a restriction or something, but then it's perfect when it's hot. Any ideas?

Hope you all fix the idle thing as easy as mine did, it's stressfull I know!

No problems with my cold starting now!! Haha! Engine temperature sensor changed and all is fine and dandy! Happy chappy now

After removing and cleaning the throttle body, the engine should be reset to 'Basic Settings' using VAG-COM in order to recalibrate the throttle body:

http://www.ross-tech.com/vag-com/cars/throttlebody.html

Buy the cable for £10 off eBay- it's incredibly useful!

I have the same issue as Dave had.

Cold misfire kinda run for half a min.

I'll follow his steps, see where that leads.

Another problem is when you turn the key on (not start just on) sometimes you can hear the fuel pump

struggling to pump... like something is running in the hose besides liquid.

Any ideas? should i clean that as well?

don't feel like spending all that time for no reason.

Another irritating common thing is when you lay off the throttle on low rpm, the car jumps back and forth for a second...

Is that the same TB prob?

Wow!

I'm so glad I'm not alone in this problem.

I'm fairly new to car maintenance but am defo going to try these solutions!

thanks for posting these steps...and we me luck!

I disconnected the battery for a few moments the other day to reset the remote locking. Since then the car occasionally (mainly on a colder engine) likes to either idle at about 15k or rev up and down between 15k and 20k. After the engine's warmed up it's absolutely fine.

I'm going to reset the ECU with this battery trick tonight once I get home to see if that works.

Thank you to the contributors of this thread!

Edited 9 February, 201115 yr by Liquidice