Sticky Throttle?
Discussion
So I am new to PistonHeads only having signed up recently. Was just wondering if anybody could help a novice out and maybe shed some light on what could be wrong.
I own a 2006 1.2l 12v VW Polo 9N3 with 46k miles on the clock and it is my first car. So far i have been loving it however a few weeks ago i noticed it had a rather rough idle which happened intermittently usually when the engine was warmed up. I noticed that the idle would drop from about 1000 to around 700 and then rumble as if it was going to stall and go back up to 1000. This would carry on until i set off again. Usually happened at junctions or in traffic.
Just today my accelerator has become very sticky. I can feel that when i change gears i am jolted forward as the revs do not drop when the clutch is applied. In addition, sometimes in neutral if i rev the car up it will either stay at say 3000rpm until i put my foot underneath the pedal to bring them back down or it will very very slowly decrease back down to idle. Obviously this isn't right.
I am most certainty not an expert but have a feeling these two issues may be linked? Could anybody please help out with suggestions as to what is the cause/ help me fix it.
Cheers,
James
I own a 2006 1.2l 12v VW Polo 9N3 with 46k miles on the clock and it is my first car. So far i have been loving it however a few weeks ago i noticed it had a rather rough idle which happened intermittently usually when the engine was warmed up. I noticed that the idle would drop from about 1000 to around 700 and then rumble as if it was going to stall and go back up to 1000. This would carry on until i set off again. Usually happened at junctions or in traffic.
Just today my accelerator has become very sticky. I can feel that when i change gears i am jolted forward as the revs do not drop when the clutch is applied. In addition, sometimes in neutral if i rev the car up it will either stay at say 3000rpm until i put my foot underneath the pedal to bring them back down or it will very very slowly decrease back down to idle. Obviously this isn't right.
I am most certainty not an expert but have a feeling these two issues may be linked? Could anybody please help out with suggestions as to what is the cause/ help me fix it.
Cheers,
James
The second problem points towards a sticky throttle. If it's cable operated then a worn cable would be my first suspect. (If the cable is starting to fray then the broken bits can snag inside the flexible outer. If this is the problem then it's only a matter of time until the cable snaps.) It could also be something physically obstructing the throttle mechanism at the engine end. You can test for that by turning the throttle spindle manually (with the engine off!) to see whether it opens and closes freely and smoothly. It could also be something simpler such as the pedal itself catching on the carpet.
The first problem sounds like a sticking/faulty idle control valve. They can get sooted up and need cleaning from time to time. There are other problems which can complicate this so you might want to sort out the sticking throttle problem before you take your spanners to the idle control valve.
The first problem sounds like a sticking/faulty idle control valve. They can get sooted up and need cleaning from time to time. There are other problems which can complicate this so you might want to sort out the sticking throttle problem before you take your spanners to the idle control valve.
GreenV8S said:
The second problem points towards a sticky throttle. If it's cable operated then a worn cable would be my first suspect. (If the cable is starting to fray then the broken bits can snag inside the flexible outer. If this is the problem then it's only a matter of time until the cable snaps.) It could also be something physically obstructing the throttle mechanism at the engine end. You can test for that by turning the throttle spindle manually (with the engine off!) to see whether it opens and closes freely and smoothly. It could also be something simpler such as the pedal itself catching on the carpet.
The first problem sounds like a sticking/faulty idle control valve. They can get sooted up and need cleaning from time to time. There are other problems which can complicate this so you might want to sort out the sticking throttle problem before you take your spanners to the idle control valve.
Hi Greenv8S, Thank you for your prompt reply The first problem sounds like a sticking/faulty idle control valve. They can get sooted up and need cleaning from time to time. There are other problems which can complicate this so you might want to sort out the sticking throttle problem before you take your spanners to the idle control valve.
My throttle body is operated by a fly by wire I'm fairly certain so i don't think that it could be what you first suggested. I probably should of mentioned the type of throttle body i had aswell but at the time was unsure. Thank you though! I took the air filter off today and had a look inside the throttle body at the butterfly plates. They seemed to be in good condition and rather clean. I also checked inside the footwell for anything that could be obstructing the operation of the pedals and found nothing. So am still clueless. I plan on doing some futher investigation this weekend going down to a friends unit who has considerably more knowledge on the subject than i do. I will update!
Cheers,
James G
If it was me I'd do a little digging into how that fbw system works. Presumably there's some sort of sensor at the pedal end. Is it a position encoder, or some sort of potentiometer? Same question at the engine end. Potentiometers can wear out, usually at the most heavily used areas which might correspond to cruising speed in top gear. The fact it seems to be throttle position dependent would tend to rule out dumb electrical faults like dodgy connections.
I don't know how much access you have around the throttle assembly - is it practical to reproduce the problem and see whether the throttle actuator is moving as you expect and how smoothly it is moving?
I guess the fbw system controls the idle speed as well so you won't have a separate idle control valve - it would be good if you could confirm that.
I don't know how much access you have around the throttle assembly - is it practical to reproduce the problem and see whether the throttle actuator is moving as you expect and how smoothly it is moving?
I guess the fbw system controls the idle speed as well so you won't have a separate idle control valve - it would be good if you could confirm that.
GreenV8S said:
If it was me I'd do a little digging into how that fbw system works. Presumably there's some sort of sensor at the pedal end. Is it a position encoder, or some sort of potentiometer? Same question at the engine end. Potentiometers can wear out, usually at the most heavily used areas which might correspond to cruising speed in top gear. The fact it seems to be throttle position dependent would tend to rule out dumb electrical faults like dodgy connections.
I don't know how much access you have around the throttle assembly - is it practical to reproduce the problem and see whether the throttle actuator is moving as you expect and how smoothly it is moving?
I guess the fbw system controls the idle speed as well so you won't have a separate idle control valve - it would be good if you could confirm that.
I think it also known as drive by wire system? I presume it's a position encoder since you can buy the throttle position sensors? I don't know how much access you have around the throttle assembly - is it practical to reproduce the problem and see whether the throttle actuator is moving as you expect and how smoothly it is moving?
I guess the fbw system controls the idle speed as well so you won't have a separate idle control valve - it would be good if you could confirm that.
I have quite alot of access to the throttle body since the engine is only small. I have yet to try that as i havn't had a friend to help so i could have a look. Could it be anything to do with vacuum leaks?
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