57 Polo 1.2 Throttle Intermittently Sticks

[union22]

I have just purchased a 57 plate 1.2 polo with 34k on the clock, all was well when I test drove it, however after my purchase and driving abut 50 miles the throttle started very intermittently sticking open. Appears more apparent in lower gears and typically sticks open at 3000rpm and will slowly close (over 5 or 10 seconds) down to normal idle.


Its very very intermittent and difficult to introduce it will be fine for twenty minutes then sticky for 5 minutes then fine again for another twenty minutes.


Only appears to have the fault when hot, once it was introduced while driving down hill and another time when I put the air con on but its so intermittent and I have been unable to reproduce the fault while driving down hills or putting on the air con since.


Blipping the throttle pedal will clear it.


On one occasion while sat at traffic lights the idle was hunting (which is hopefully a clue to the problem)


No errors seen in VCDS.


I have squirted some carb cleaner into the throttle body and wiped out with a cloth also manually opened and closed the butterfly, it is/was oily below the butterfly! Also used VCDS to do a throttle body alignment. But fault is still there.


Before I bought the car it may well have been stood for some time therefore the fault just may clear it’s self!!!


Plan to log some data with VCDS but I have two issues 1. I don’t know which blocks to monitor and what sensors I need to look at and 2. VCDS on my laptop keeps hanging after about 5 minutes.


Anyone else had this issue or any advice?

[union22]

After some research reading forums etc there are two theories:-


A faulty clutch pedal switch. Apparently sometimes this does come up on a fault code read but often the person reading the codes has to go into measuring blocks 066 and look at the Binary digits which show pedal position. In zone 2 there is an eight digit block, with no pedals pressed this reads 00000000, with the brake pedal pressed this changes to 00000011 and with the clutch pedal pressed, 00000100 so with both pressed it reads 00000111. If the value is 00000100 with the pedal not pressed the switch is stuck on and if it says at 0 all the time, the switch is stuck off. The values in positions 1 to 4 are not important. What you want to see is 00000000 with the pedal up and 00000100 with the pedal down.


Or may be due to a sticking throttle valve positioner unit. With VCDS you can test this in output tests.


But I am not convinced that these two theories relate to my problem as I once got a hunting idle!!!!


I need to get some decent log files with the fault to further diagnosis plus run output tests. Will let you know what I find. Anyone any ideas?

[zollaf]

its 9 years old and done 34k, first thing i would do is drive it a lot. its probably just stuck from not being used. chances are it will soon clear itself. if not, a thorough clean of the tb may help.

[union22]

I have found a problem- the clutch pedal switch. Using VCDS measurement blocks 066 zone 2 reads 00000000 with the clutch pedal pressed (should read 00000100), after disconnecting the switch VCDS reads 00000100. And using a multimeter on the switch it makes a circuit pressed or de-pressed. Therefore ordered a new one.


The faulty clutch pedal switch explains the sticking throttle (rev hanging) but a bit strange why it was intermittent when the switch is completely broken and why the revs occasionally hunt while stopped at tragic lights. I guess its just the logic of the software or I have two problems, but will know for sure when I fit the new switch.