Car revving when idle? - MK4 Golf 1.4 Petrol
Discussion
Hi,
I went to see a Mk4 1.4 MATCH today, all was good.
After a test ride, I left it with engine running, and it was just revving up and down a small amount, is that normal? That was the first start of the car today so it may have been cold?
And on my second ride, the revving did not occur.
So I did not buy the car, only because of that. Can someone tell me if there is nothing to worry about?
Also the gearbox was a bit rigid, is that normal for a VW? Thanks
I went to see a Mk4 1.4 MATCH today, all was good.
After a test ride, I left it with engine running, and it was just revving up and down a small amount, is that normal? That was the first start of the car today so it may have been cold?
And on my second ride, the revving did not occur.
So I did not buy the car, only because of that. Can someone tell me if there is nothing to worry about?
Also the gearbox was a bit rigid, is that normal for a VW? Thanks
The phenomenon you describe is 'hunting'.
You didnt say what year the Golf was.
I'm assuming it was a Golf 3 or after.
In which case- its likely to be the idle speed control motor- or it just require a cleaning out of the lines.
I doubt it's anything major- I wouldnt have NOT bought the car (except for the fact its a Golf 1.4
) but gotten money off.
You didnt say what year the Golf was.
I'm assuming it was a Golf 3 or after.
In which case- its likely to be the idle speed control motor- or it just require a cleaning out of the lines.
I doubt it's anything major- I wouldnt have NOT bought the car (except for the fact its a Golf 1.4
) but gotten money off.It's a 53 plate Golf.
Other people on a GOlf forum have said:
- Carbon building up in the throttle body housing is a common thing, and could be the cause of the irratic idling.
- If it's "bouncing" at a rate of about 1 second I will put money on a vacuum leak. Check all hoses connected to the inlet manifold for splits especially the rigid brake servo pipe. They are difficult to spot, look very carefully up to the non-return valve and at the RHD to LHD conversion connector.
A complete brake servo pipe is made of 2 pieces about £40 to replace. Could be throttle body though but "bounce" is usually unmetered AIR getting in!
Other people on a GOlf forum have said:
- Carbon building up in the throttle body housing is a common thing, and could be the cause of the irratic idling.
- If it's "bouncing" at a rate of about 1 second I will put money on a vacuum leak. Check all hoses connected to the inlet manifold for splits especially the rigid brake servo pipe. They are difficult to spot, look very carefully up to the non-return valve and at the RHD to LHD conversion connector.
A complete brake servo pipe is made of 2 pieces about £40 to replace. Could be throttle body though but "bounce" is usually unmetered AIR getting in!
From my experience if a car sits and revs at idle, if its a steady high rpm - 1500-2000 then its possible an air leak. Something VERY simple is the cause 99.9% of the times, being a rubber intake hose that is split after the MAF sensor so the engine is running lean by pulling in unmetered air with little resistance of the throttle plate.
If the the revs are unstable at idle, moving up and down (hunting) then this usually a problem with something like the throttle butterfly being stiff, making the idle control slow to react. Being a VW thought, it is likely to have the notorious VAG Idle Control valve which leaves the throttle butterfly shut and has a bypass with an electronically controlled throttle just to keep the car idling. These things have a small butterfly valve inside that gets oiley from the oil coming from the rocketr cover or bottom end pressure return hoses. Thus the units often get clogged and cause problems with sticking. A simple fix if it is an idle control valve is to take it out (one clip and a screw i think) and then blast the hell out of it (inside of it using a spray nozel) using carb cleaner... or even WD40 which helps to shift all the crap build up and lubricate the parts. Very easy job and should always be part of regular maintenance on an old VW/Audi. You can tell if it had an idle control valve as it is a black/silver cylinder about 35-40mm diameter and about 75-80mm long with a hose connector top and bottom and sits next the the throttle body.
Hope this helps!
If the the revs are unstable at idle, moving up and down (hunting) then this usually a problem with something like the throttle butterfly being stiff, making the idle control slow to react. Being a VW thought, it is likely to have the notorious VAG Idle Control valve which leaves the throttle butterfly shut and has a bypass with an electronically controlled throttle just to keep the car idling. These things have a small butterfly valve inside that gets oiley from the oil coming from the rocketr cover or bottom end pressure return hoses. Thus the units often get clogged and cause problems with sticking. A simple fix if it is an idle control valve is to take it out (one clip and a screw i think) and then blast the hell out of it (inside of it using a spray nozel) using carb cleaner... or even WD40 which helps to shift all the crap build up and lubricate the parts. Very easy job and should always be part of regular maintenance on an old VW/Audi. You can tell if it had an idle control valve as it is a black/silver cylinder about 35-40mm diameter and about 75-80mm long with a hose connector top and bottom and sits next the the throttle body.
Hope this helps!
In that case its a a much smaller issue. Exactly what its hard to say. The more modern VW engines (I hadn't noticed you said mk 4) they have load sensing on the engine that senses when something like the air con is turned on loading the engine at idle and provides more throttle to keep the idle stable. Sometimes these senses along with a wearing idle control valve can cause small irregularities in the idle, especially if the engine is cold as you have all these different systems and the auto choke all working together to keep the engine as near to stable as possible.
As a result this really isnt something to think twice about. The only time to worry is if warm it does it alot and it becomes noticable more than 2-300 rpm up or down. If it went away on a second (presumably already warmed up) drive then its absolutly fine - just the ECU juggling different systems.
As a result this really isnt something to think twice about. The only time to worry is if warm it does it alot and it becomes noticable more than 2-300 rpm up or down. If it went away on a second (presumably already warmed up) drive then its absolutly fine - just the ECU juggling different systems.
Coldplay said:
It's a 53 plate Golf.
Other people on a GOlf forum have said:
- Carbon building up in the throttle body housing is a common thing, and could be the cause of the irratic idling.
- If it's "bouncing" at a rate of about 1 second I will put money on a vacuum leak. Check all hoses connected to the inlet manifold for splits especially the rigid brake servo pipe. They are difficult to spot, look very carefully up to the non-return valve and at the RHD to LHD conversion connector.
A complete brake servo pipe is made of 2 pieces about £40 to replace. Could be throttle body though but "bounce" is usually unmetered AIR getting in!
If its a modern multi point injected car, I dont see why you would have carbon build up on the inlet throttle, as the fuel (which is the source of most carbon deposits) is injected into each port. Carbon build up could happen due to external EGR- but I dont think this would cause eratic idling.Other people on a GOlf forum have said:
- Carbon building up in the throttle body housing is a common thing, and could be the cause of the irratic idling.
- If it's "bouncing" at a rate of about 1 second I will put money on a vacuum leak. Check all hoses connected to the inlet manifold for splits especially the rigid brake servo pipe. They are difficult to spot, look very carefully up to the non-return valve and at the RHD to LHD conversion connector.
A complete brake servo pipe is made of 2 pieces about £40 to replace. Could be throttle body though but "bounce" is usually unmetered AIR getting in!
Air leaks are usually easy to spot, I would spray 'easy start' or some other combustible fluid- even WD40 will do it, liberally over the intake and the suspect leak area with the engine running, and the revs will rise when you've hit the correct region.
Good luck
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