Firstly hello to the ClubPolo Forum!

Right so I recently got a ‘98 1.4l 16v Polo, Engine: AFH (first car actually) and virtually from the off I’ve been having problems. What follows is quite a lengthy account of my experience to date but hopefully it may lend some clues as to what the underlying problem could be?

Firstly it began cutting out and hunting for revs, the usual and apparently not uncommon thing where it cuts out when dipping the clutch on the approach to traffic lights and hunting for revs when idling at standstill. I found the 2 threads about cleaning the throttle body and replacing the temperature sender and decided to do both. I am a complete newbie and have no experience with this kind of thing until now so I enlisted the help of a mate of mine before attempting it. It was a couple of weeks before we had a chance to do it & just before then the problems just stopped completely one day!? I had been driving too and from work everyday, a short blast up the motorway, so we figured that had cleared out the throttle and engine and got itself working again.

We gave the engine a look over anyway, checked the throttle body to check for fouling and it was virtually pristine. Had a look through the history and found that it had been replaced completely not long back (more on that later). Also checked the plugs which looked fine. I had picked up a temp sender from GSF but decided not to change it at that point as it was running ok.. if it ain’t broke...

A short while later I noticed that it seemed to be losing a bit of power and the acceleration wasn’t quite as good, quite a subtle change at first. When I got the car the seller mentioned that just before he came to sell it the cat had gone and there was a noticeable rattle coming from it. I didn’t think much to this at the time but knew I would have to be done it at some point. When it started losing power I thought that as the cat had gone the bit of the broken monolith could possibly be rattling round inside causing more bits to break and clog up the exhaust causing the loss of power? At any rate it needed doing so got one from GSF and took it to a garage to get it put on. Over the course of the week the performance had gradually been getting worse and I noticed that it was getting thirsty. Then on the way to the garage the idle become really rough/lumpy and it was struggling to pull off from standstill and kind of stuttering/juddering really badly all through 1st, 2nd & 3rd until it got going.

The garage changed the cat but told me that it was still had a problem. The idle was still quite rough and it was running really rich, you could smell petrol coming out the back. They recommended a full service and that I put an additive through it to clean the injectors. The next morning I took it in to get it checked out. I explained that I knew it didn’t need a full service as we had already checked the oil, air filter, plugs etc.. and all was fine and asked if they could do anything else to pin down the problem. They ran a diagnostic check which came back with nothing. They put the injector cleaning additive through it and changed the plugs. They thought it might be the coil pack so they picked one up ready to put in but when they went to do it they found that the one in there looked new so left it. It was then running a bit better and idling ok, they ran an emission check and it was still putting out a lot of unburnt hydrocarbons. They tested the lambda sensor and said that the readings were all over the place. They also mentioned that it was quite erratic, one minute it’ll idle fine and the emissions are ok the next it would get a bit rough and start chucking out petrol again. They suggested that it could be a faulty lambda sensor and that I should get that done next, they could do it for £100 supply and fit but it might not solve the problem. At this point I was starting to worry about my finances so I decided to take it home and not drive it until I had a better idea of what to do next, mainly because I’m wary that I could ruin another cat if I keep driving it while it’s putting petrol out the exhaust.

I gave it a couple more short drives, noticed that when starting from stone cold it started easily and was running ok, it was only after 4-5mins when it began to warm up that it started getting rough again, so must be temperature related. Then decided to change the temp sender and the lambda sensor, got a bosch universal sensor, changed them both and reset the ECU. When we first started it up it seemed to still be a bit lumpy for like a minute but then sorted itself out. After that it seemed fine & ran well for a couple of weeks.

Then I noticed that it seemed to be taking a long time to get up to temperature. It would vary from 10mins to up to 30mins on the motorway, and occasionally it would get up to 90 and then just drop off again back to nothing while driving. I and found a thread or two on here that pointed towards a faulty thermostat and/or housing. I got a replacement thermostat and housing, drained the coolant and replaced both, didn’t find any leaks around the housing before changing it. The old thermostat was stuck with the pin sticking out and next day it was getting up to 90 straight away (quickly actually, only a few minutes) and it was staying at 90 dead in the middle. However, then the rough/lumpy idle returned with a vengeance! This time it would idle at 1000 then drop to around 500 & flick between the two sounding really “chuggy” in the process and just barely not stalling. Again it was ok when cold but as it warmed up the idle got rough, occasional drops in power and a worrying judder.

Have been trying to think what we could have done when changing the thermostat to mess things up. While we drained the coolant when we opened the housing a bit did come out and leaked over the cable splice for the new lambda sensor. I took that off, opened it up and thoroughly dried it out just in case but it looked ok. We also had a look in the throttle body and found a big bit of crud inside ( looked like someone had gobbed in there), which must have come from the breathing tube. We cleaned it all up with some carb cleaner, reset ECU and started it again with the lambda plugged in. The rough idle was still there. Unplugged the lambda tried it again, ran ok for maybe 30 secs then rough idle returned. It sounded like maybe it wasn’t firing on all cylinders so we disconnected the leads one by one and started it up each time. I think there was a noticeable change in the noise but it did started each time and ran on 3. We reset ECU again, plugged it all back in and took it for a drive. Then things got really bad....

The stuttering/judder returned badly, it seemed like it was flicking from running on 4, then down to 3, then even down to 2 then back to 3 cylinders with brief flashes of it running on all 4. After at bit it started to smell like it was getting really hot (although the gauge still said 90) and seemed like it was on the cusp of dying completely, had to keep on the accelerator to stop in stalling. We stopped to let it cool for a bit then set off to get it home, ran better for a few minutes then back to rubbish. Same story again today.

Really not sure what the problem is now. It seems to still be temperature related and must be affecting the fuel mix that is getting sent causing it to run rich?

The history shows that it went to a VW garage twice in 2009. The reports state that it went in with high idling problems. 1st time round they found that the injector seals were leaking, replaced them, checked cambelt timing, checked ignition timing, carried out basic settings and adaption on the throttle body, did an emissions and road test and it then seemed to run ok. The next report is for 1 month later, this time: rechecked work from previous visit, found lambda readings out of spec, replaced lambda, replaced throttle body, but problem still persists... and then nothing!? So it seems like the VW garage just gave up!?!

So maybe the underlying problem may have been ongoing for some time now. Virtually everything that is usually responsible has been replaced (sometimes more than once!) and yet the problems go on.

I was thinking that maybe the ECU was knackered as I have read that the ECUs for this engine(Code: 030 906 030D) are known to be faulty, but could a faulty ECU cause all of the above. The problem seems to be intermittent as it seemed to run well before we did the thermostat (although the changing of the thermostat could be incidental, suspect the problems would have probably returned anyway). This leads us to think that it could be a problem with the wiring somewhere? Maybe a short circuit? The other thing that someone has just recently mentioned is that it could be the MAP/thrust sensor?

Apologies for the lengthy post but I starting to get a bit desperate and there must be a solution. Looking on the net it seems that I’m not alone in my suffering, lots of 16v Polos with similar problems? To add to that, in the albeit brief periods when it’s been working well I’ve become quite attached to my Polo and I’m determined to keep the little b*stard :-D

Anyone have any suggestions or advice on what I can do next? Any advice on how to go about testing the wiring would be a great help, or is there anything else people think it could be? Any help hugely appreciated!!!

Edited 25 March, 201115 yr by Alun_16v

lol you referenced two of my threads in there XD

anyways, seems to me you changed everything that could cause rough running, could try getting the injectors cleaned with an ultrasonic tank as the redex things dont realy work too well. i think if there was a short in it the diag machine would pick that up, my mate took his car to an auto electrician and they found wireing problems with a diag machine.

not realy sure what to suggest but ill keep an eye on this as I'm a few steps behind you atm, I'm doing my lambda temp and exhaust when i get paid as its driving like a bag of shite atm

Clearly good threads then :-)

I think the next thing we're going to do is open up and clean out the inlet manifold, see if we can't find that MAP/thrust sensor and see what kind of state that's in. See what difference that makes.

Then I'll prob investigate injectors and wiring. Auto electrician eh? Prob a good idea if I track one of them down. I had thought that I'd prob end up checking the loom and each wire and connections manually, can't say I'm overjoyed by the prospect of having to do that.

thing is with sensors u cant look at them and say theyr ok, they are electrical componants so u would need diag equiptment to work out if they are working, same as wireing, could be a break in the wire somewhere u cant see (multimeter works for that though)

think were along the same lines with our polos atm, tho mines only an 8v :( ill see what i can get sorted on mine and see if it helps.

random thing with mine, if I'm sitting parked, engine running with windows closed...i press the window up button and the idle drops, the dash lights and headlights go noticably dimmer till i release it :S

random thing with mine, if I'm sitting parked, engine running with windows closed...i press the window up button and the idle drops, the dash lights and headlights go noticably dimmer till i release it :S

The reason for this is the alternator is struggling to keep up the demand for the current, the window motors draw around 7.5~10 amps more if you window mechanism is a bit stiff, so at idle with the lights on the voltage will drop and your revs will also drop as the extra load the alternator puts on the engine too try to maintain the correct output for the electrical loads put on it

thing is with sensors u cant look at them and say theyr ok, they are electrical componants so u would need diag equiptment to work out if they are working, same as wireing, could be a break in the wire somewhere u cant see (multimeter works for that though)

Yeah good point. Speaking to someone about this they said that they knew someone who had a 16v Clio with intermittant power loss. After much searching they eventually cleaned the air flow sensor and it sorted it out completely. I'm hoping that is going to be the case with mine but I could just be being over optimistic. I may just replace it althogether as I think you can pick one up pretty cheap on ebay, will see.

It'll prob be the weekend before I get a chance to tinker next but I'll be back with an update after then.

random thing with mine, if I'm sitting parked, engine running with windows closed...i press the window up button and the idle drops, the dash lights and headlights go noticably dimmer till i release it :S

The reason for this is the alternator is struggling to keep up the demand for the current, the window motors draw around 7.5~10 amps more if you window mechanism is a bit stiff, so at idle with the lights on the voltage will drop and your revs will also drop as the extra load the alternator puts on the engine too try to maintain the correct output for the electrical loads put on it

so its normal then? hasnt realy bothered me so havnt asked till now lol

I had esacly the same problem, mine turned out to be cam timing!

Id suggest given all you are tests i take it u had you are throttle body reset via a vagcom?

You checked stuff like maifold sensor, fuel pumps

My money would be on the throttle body, i highly doubt the previous owner bought it new and beleve me once its changed on a car you are motor is NEVER the same

Try these as from my experience these are common, failing that take a no nonsense approach with the garage, take it to a proper mechanic or a vw specialist and say u want you are car sorting no ifs and buts if it dnt solve the problem then u aint payin i did they soon sorted the problem lol

My money would be on the throttle body, i highly doubt the previous owner bought it new and beleve me once its changed on a car you are motor is NEVER the same

I've got receipts in the history for a new throttle body from Europarts, and then on the 2nd receipt from the VW garage it states that they suspected that non-genuine TB was the cause so replaced it with genuine VW one. So its actually had 2 new TBs and I guess they were put in to try and fix the orig problem. So yeah I guess replacement TBs could be exasperating the problem.

Try these as from my experience these are common, failing that take a no nonsense approach with the garage, take it to a proper mechanic or a vw specialist and say u want you are car sorting no ifs and buts if it dnt solve the problem then u aint payin i did they soon sorted the problem lol

This is going to be my absolute last resort. I suspect they'll prob try and charge me £500 for a new ECU with no guarantees so it may take some talking to ge them to agree to any guarantees. Gona try every other thing I can think of first before I go to VW to assume the position.

This weekend, gonna check manifold inlet, MAP sensor, TB calibration with VCDS (hope you can do it with Lite cos that's all I can afford right now), failing that I'll look into wiring and Cambelt timing.

To update...

Yesterday we took the inlet manifold off and it looked pretty grimey inside. I guess that spraying carb cleaner through the throttle body is going to have to affect of just shifting the stuff further down although I don't know how heavy the build up would actually have to be to start having negative affects on the running. Have now given it a good clean with carb cleaner and petrol and its looking a lot better. We cleaned it without opening it up fully mind as we didn't want to risk leaks when putting it back together, would prob need new gaskets and the like. Nevertheless, tis looking loads better now.

The MAP/Thrust sensor (the actual sensor part that looks like a small resistor) was pretty oily but have given it a blast with some carb cleaner and now it looks ok. I'm trying to decide whether I should replace anyway it just in case? Anyone know of an easy way to test whether or not its working correctly?

We took the dizzy cap off to have a look and it seems to be quite loose and there was moisture inside!? So going to replace that as well as the rotor arm. In fact the distributor rotor arm contacts look a bit oily and grimey (pic attached), which is a bit weird no? Anyone got any advice on how best to clean it up?

The breather pipe had been chucking up some sludge into the throttle body so had a look at that. There is an "oil separator" before the tube and when taking that off a load of water leaked out!? Does that means the oil has water in? Going to do an oil and filter change as a precaution. The oil separator seems a bit gunked up although I'm reluctant to replace just in case as they are £70 from VW. Considering just blanking this off if its going to risk chucking more sludge through.

I also think that maybe the EGR valve could be causing the problems and am trying to decide whether I should just blank it off to see whether it makes a difference. Is this just a case of putting a blanking plate (or even just a piece of a drink can) to block the hole where it is fixed to the exhaust manifold?

FIXED!!

So put my car back together last night and now it seems to be running sweet again; idle settles nicely, heating circuit working fine and it's pulling well :-D

What we did: as mentioned before we'd taken the airbox, throttlebody, fuel rail, inlet manifold, oil seperator, distributor cap and 4 hoses off.

We replaced all 4 vac hoses: one going from the thrust sensor to the fuel rail, one from throttle body to some air filter sensor, a small bit attached to the sensor/air filter and the hose to the EGR valve. We'd given both the MAP/thrust sensor and inlet mani a good clean with petrol and/or carb cleaner. Gave the oil separator a good rinse out with petrol (loads of crap came out of that). I refer you to this particularly interesting thread for reference: http://www.clubpolo.co.uk/forum/lofiversio...hp/t181765.html

We're gona keep an eye on the oil separator and breather getting gunked up again and I'm hoping that keeping it clean is going to give me some extra mpg.

We blanked off the EGR valve at the throttlebody end with the old bit of coke can blanking plate technique. We didn't bother trying to get it off the exhaust manifold as it's on really tight but I suspect that it's stuck open. Anyway, sounds like it should pass the emissions test blanked anyway so prob going to leave it as it is as long as that doesn't cause further problems.

Gave the distributor and cap a good clean out. Bit concerned that there is water getting in there so going to keep an eye on it and prob replace the cap at some point.

Next thing on the list is to run a flush of cheap oil with ATF in to give it a clean out and then put some decent oil back in. Would be good to do and might help the breather gunking situation as well.

Is your car stil running ok,as my car is doing the same as you have described,

Hi,

 

I’d just like to say I appreciate your thread 13 years later as I have used it as a basis for my own mk4 polo 2006 suffering from almost the exact same issues, and I am going to fix them because as you said, I am attached to this bugger and don’t want to let him go.

 

I am currently about to clean my map sensor with break cleaner and oil separator too, if anyone is interested I’ll update you on how it comes along

 

@ConThomas please bear in mind that the little thing poking out the front of the MAP sensor is the air temperature sensor, not the pressure sensor. I think a lot of people see that bit looking really grubby and coated in oily soot and think, "ooh that just needs a clean and then it'll all be good".  The pressure sensing bit is deeper and inaccessible. Very rare for this type of problem to be anything to do with the MAP sensor.

 

Have you checked spark plugs and read codes to see if any fault info is stored? 

Hi Pete, thanks for the reply, 

 

Yes I have no current fault codes, 

 

I am currently trying to understand these issues.

 

When I dip the clutch while coming up to lights sometimes it will drop to 500revs or slightly higher before climbing back up to idle again.

 

yesterday after doing about 90 miles with a loaded car I got stuck in motorway traffic and this time the revs every other clutch dip or so would drop as low as 400 and stay for slightly longer before climbing again.

 

sometimes ive had it where I’ve tried to pull off or out of a junction and it’s completely bogged down, technically stalled on me and revived its self. 

 

I also have very raised fuel trims and if I am not on motorway I get terrible MPG
 

I’ve checked and done the following: had a new service every 6k since my ownership, 

 

seems to be no vac leak on break booster pipe (most common area of fault) but I am double checking with butane gas today 

 

No blow by, no burnt valves, (cowboy tested with tissue at exhaust for valves and looking for slight suction) and when u take oil cap off it has slight suction so okay that end I presume.

 

i was going to clean map sensor with break cleaner but if you think this will be pointless then I will save the hassle as it’s already awkward enough to get to.

 

and I was going to clean oil seperator today also.
 

Is there anywhere else I should be looking ?  

 

 

 

 

 

 

 

 

 

 

The oil separator is really awkward to clean out, unfortunately, it has a lot of convoluted passages within it.

Do you know what your engine code is (reg number or VIN would allow me to check for you)?

Do you know what pressure rating the regulator part of the current fuel filter is? Incorrectly rated replacements are sometimes suggested by the like of ECP.