Lupo 1.4 16V AUA throttle valve behavior

[P.Lindblom]

Some of you might have seen my other thread about the extremely annoying throttle problem: http://forums.clublupo.co.uk/index.php?showtopic=73365

If I push the throttle just a little bit and hold it in position the revs go up and down like a rollercoaster. I just had my gf record what the throttle valve was doing. Is this behavior normal?

This is what it does when I just turn on the ignition

http://www.youtube.com/watch?v=vipQghEjf3Q

Engine start and at 0:15 light, constant throttle. Why isn't the valve doing what the pedal is doing?

http://www.youtube.com/watch?v=Rqw5nQOO588

[treblet]

Your videos are set as private.

We can't view them.

[P.Lindblom]

Your videos are set as private.

We can't view them.

Oops, sorry. Now you should be able to view them.

[treblet]

Throttle position sensor maybe?

When did you last change your lambda sensor?

[P.Lindblom]

Throttle position sensor maybe?

When did you last change your lambda sensor?

I've got a feeling it could be the TPS. It's inside the throttle body isn't it?

Not sure about the lambda. I just bought the car, but the emissions were fine at the MOT about six months ago.

[treblet]

Only reason I wondered about the Lambda is that there isn't any air mass meter, the air intake is controlled via the burnt gases so if your lambda is damaged it could cause bad fuel/air mix, however if it was fine and ran okay before this then it's probably not that.

Looks a lot more like a TPS problem.

[DanGB]

Mine occasionally does that, where it revs up and down perhaps 100 revs every second. Rarely happens so not done anything about it.

[P.Lindblom]

Only reason I wondered about the Lambda is that there isn't any air mass meter, the air intake is controlled via the burnt gases so if your lambda is damaged it could cause bad fuel/air mix, however if it was fine and ran okay before this then it's probably not that.

Looks a lot more like a TPS problem.

I see. That's definitely something to look into. I'll check how much new lambda sensors are.

Mine occasionally does that, where it revs up and down perhaps 100 revs every second. Rarely happens so not done anything about it.

Mine does it when it's warm. I just found this thread: http://www.volkszone.com/VZi/showthread.php?t=398806

right ... car is done and running sweetly again. Found more than one fault in the end so here goes with what we found

First of all after doing a compression test we found that cylinders 1 and 4 were down on compression.We found the reason for this was the fact that the camshaft and followers on those cylinders were badly worn(pics will follow tomorrow).

The head was replaced with a good 2nd hand item which had no signs of camshaft wear.

Once the head was on and torqued we ran the vehicle up to temp ... it still had a slight fluctuation in idle at times... we found a tiny nick in one of the inlet manifold seals .... changed that and it ran much better ... there were a couple of fault codes logged in the ECU which needed to be cleared out .. which IIRC were that basic settings hadn't been carried out ,mixture adaption present and also that lambda control was on the limit.

Once we had done the basic settings and changed the pre cat lambda sensor it drove like a new car.FYI the car in question is a 98 R Arosa with 33k miles.

Hope this helps out with your car and gets you back on track

Now I'm suspecting my camshafts or my head. I will do a compression test later today.

[P.Lindblom]

I haven't had a chance to do a compression test, but I've more or less excluded the possibility that my throttle body is faulty. I just borrowed and tested two more TBs with exactly the same results. Could the gas pedal somehow cause the throttle valve's nervous behavior?

[kabman]

I haven't had a chance to do a compression test, but I've more or less excluded the possibility that my throttle body is faulty. I just borrowed and tested two more TBs with exactly the same results. Could the gas pedal somehow cause the throttle valve's nervous behavior?

I'd check the MAP sensor, compression, cam timing, look for any air leaks in the intake manifold (breather hoses, vacuum hoses, brake servo, etc).

I had a similar problem and, after exhausting all other posibile faults, found the cam belt was one tooth out!

[Defcon5]

On your second video I was panicing that that black clip that is wobbling about was going to drop down the throttle body!

[P.Lindblom]

I'd check the MAP sensor, compression, cam timing, look for any air leaks in the intake manifold (breather hoses, vacuum hoses, brake servo, etc).

I had a similar problem and, after exhausting all other posibile faults, found the cam belt was one tooth out!

Thank you for your reply. I got another reply in the other thread as well.

do you still have problems with this?

My car has done this really badly since the engine was refitted, had a good look at it yesterday, and when we took of the vacuum pipe from the fuel rail it ran perfectly?

We found a spare tube and fitted it, its not perfect but its 100x more better! down to the plastic part of the tube sitting loose in the rubber attachment ends.

Can't be sure if it will be your issue but won't hurt to try it?

Let me summarize:

[X] Clean throttle body

[X] Do a throttle body alignment

[X] Change oil & oil filter

[X] Try injector cleaner

[X] Replace air filter

[X] Replace spark plugs

[X] Replace HT leads and coil pack

[X] Try another throttle body

[ ] Do a compression test

[ ] Check MAP sensor

[ ] Check the cam timing - How do you check that?

[ ] Look for air leaks (breather hoses, vacuum hoses, brake servo, etc) - Is there a list of all vacuum hoses so I can just order new ones?

[ ] Replace vacuum pipe to the fuel rail?

[ ] Replace fuel filter

Edited April 25, 2011 by P.Lindblom

[kabman]

[ ] Check the cam timing - How do you check that?

First, find TDC on cylinder1. You can do that by looking at the crank pulley but an easier way is to remove the plug from cylinder1, poke a long screwdriver or something similar in until it touches the piston, turn the crank pully until you feel the piston reach it's highest point (you may have to turn the puley back and forth until you find the right spot).

Next, whip off the top part of the cambelt cover and check that the holes in the cam pulleys line up with the holes in the head. You can use 8mm drill bits to line them up.

Have a look here for more info.

timeing belt procedure

[P.Lindblom]

I did a compression test yesterday and all four cylinders reached 14 bar (~200 psi). One more thing off the list then.

[X] Clean throttle body

[X] Do a throttle body alignment

[X] Change oil & oil filter

[X] Try injector cleaner

[X] Replace air filter

[X] Replace spark plugs

[X] Replace HT leads and coil pack

[X] Try another throttle body

[X] Do a compression test

[ ] Check/replace MAP sensor

[ ] Clean/replace EGR valve

[ ] Check the cam timing - How do you check that?

[ ] Look for air leaks (breather hoses, vacuum hoses, brake servo, etc) - Is there a list of all vacuum hoses so I can just order new ones?

[ ] Replace vacuum pipe to the fuel rail?

[ ] Replace fuel filter

First, find TDC on cylinder1. You can do that by looking at the crank pulley but an easier way is to remove the plug from cylinder1, poke a long screwdriver or something similar in until it touches the piston, turn the crank pully until you feel the piston reach it's highest point (you may have to turn the puley back and forth until you find the right spot).

Next, whip off the top part of the cambelt cover and check that the holes in the cam pulleys line up with the holes in the head. You can use 8mm drill bits to line them up.

Have a look here for more info.

timeing belt procedure

Thank you I will try that as soon as I can.

I've recently noticed another strange behavior which I think is caused by the same problem. When driving slowly (around 30mph) in 3rd 4th or 5th gear at low throttle the car feels kind of jerky. It feels like short, intermittent misfires. As long as I'm accelerating or driving fast it's smooth though.

Edited May 2, 2011 by P.Lindblom

[kabman]

I've recently noticed another strange behavior which I think is caused by the same problem. When driving slowly (around 30mph) in 3rd 4th or 5th gear at low throttle the car feels kind of jerky. It feels like short, intermittent misfires. As long as I'm accelerating or driving fast it's smooth though.

I had the same symptom, as well as hunting at idle. It was cured when I reset the cam timing.

[P.Lindblom]

I had the same symptom, as well as hunting at idle. It was cured when I reset the cam timing.

That sounds interesting. Resetting cam timing, does that mean physically aligning the camshafts or is it some sort of Vag-Com command?

[CasperGTI]

Is this happening all the time? so when the car is warm or from cold start? and you only see something happening at idle or throughout the rev range?

What spark plugs are you using? Id recommend only using OEM ones as we have seen many problems caused by aftermarket plugs.

That is normal behaviour for an electronic throttle, as the lupo has no IACV it uses the throttle as its idle control which is monitored through RPM and MAP data. They do have a tendency to get corroded motor position contacts, you can check this by unclipping the black cover of the electronic part of the throttle IIRC. I would check these issues before you go throwing parts at it.

EDIT: I just realised you have tried a few TB's. Id have a look at your timing then MAP sensor next.

John

[smitty12]

Was this problem resolved? I've got the same thing with the sport engine i've just put in my lupo

[kabman]

That sounds interesting. Resetting cam timing, does that mean physically aligning the camshafts or is it some sort of Vag-Com command?

Physically adjusting the camshafts. Someone had replaced the main cam belt and got it one tooth out. It's an easy mistake to make since there are two very simliar timing marks on the front cover.

[P.Lindblom]

Today I had VAG check the car and they couldn't say what is causing the problems. They did a whole bunch of tests and discovered that the engine is misfiring intermittently on cylinder 3. They told me it's probably caused by either:

1. A bad injector

2. Intermittent loss of compression in cylinder 3 (is that even possible?)

I really really hope it's just the injector. I'm so tired of this car right now, but if I could at least get it running properly I would probably be able to stand all the other small issues. A new injector is £180 so I'm going for a second hand one for £40, but first I'm going to ask the mechanic how they figured out which cylinder is misfiring. Then I'll swap the no. 3 injector with one of the others and see if the problem follows.

By the way, is cylinder 3 the third from the left or from the right if you're standing in front of the car looking at the engine?

[kabman]

The usual convention is to number cylinders starting at the front of the engine where the pulley is, the gearbox being at the back of the engine.

So, as you're peering under a Lupo's bonnet, the front of the engine is on the left, the gearbox is on the right and cylinder 3 is the third from the left.

[P.Lindblom]

I just replaced the temp sensor and the car misfires as usual. I've now given up completely. I'll sell this car as soon as I can and I won't buy an old VW again.