Lumpy / Poor Idling Golf MK4 1.4 16V

8 Nov 2006
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United Kingdom
Dear All

I have a VW Golf 1.4 16 Valve 2001 Reg. The Car is suffereing from Poor / Lumpy idling when Hot. When the car is cold the idling is fine and the engine runs smoothly till it gets hot and then sometimes it idles smoothly sometime not!

Steps taken, Replaced HT Plug Leads, Spark Plugs. Cleaned Breather Hose and Oil seperator Box. Cleaned Throttle Body, disconnecetd battery and let ECU re-align throttle body. Added BGK44 fuel Cleaner to Petrol Tank and made a slight improvement!

PLease does anybody have any ideas what the problem could be as I have tried all I know? Many thanks.
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Did you get the fault codes read? Local garage will do it for you and tell you the fault codes present (if any). If you are on a budget, ask the price first.

This will point you in the general direction of the fault. Would you have any air leaks into the inlet manifold, due to perished or loose small bore piping? Idle Air Control Valve (IAC) might need a clean?
No Fault Codes indicated as car was plugged into diags machine, Idle steady at 900 RPM but engine rocks backwards and forward really badly shaking the whole car!

Not sure if this car has an Idle Control Valve? If so where abouts is it located?
I had pretty much the same symptoms on my Mk3 1.8. Turned out to be a hole in a vacuum pipe. Problem finding it was because without the engine running the split was nigh on invisible, only opening up to cause problems when it went under vacuum.

If you can't find any splits or holes just by looking then the following is the technique I used to find it (and I'm not sure it is a particularly safe or sensible way to proceed!!) - I took my propane blowtorch, turned on the gas (don't light it!!) and slowly run the propane over all the vacuum pipes you can acess whilst the engine is running. When you run it over a split or hole you will hear the engine even up and increase revs. I believe others recommend using carb cleaner to do the same thing, but I wasn't convinced about blasting volatile liquids into a hot engine bay. Either way do it outdoors and only if you are comfortable with the possible risk of blowing yourself up :D

edit This was the culprit (manifold to brake servo pipe), it had been rubbing against one of the braided earth straps:
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Yes checked all the hoses including Servo Pipe to throttle body each one is fine. When I broken the Servo pipe seal the pressure was released as expected.

I even cleaned out the EGR Valve just in case but problem is still there! Renewed Throttle body gaskets as well just in case!
It's still worth trying a gas check on those vac lines, the splits can be really easy to miss. I spent literally days with a a good torch looking over mine and failed to find it. Found it in a couple of minutes with the propane :)

The only other suggestion I got at the time was a that a lifter may be pumping up holding a valve open.

I'm not sure if this is allowed here but the Technical section over at vwvortex ( is populated with knowledgeable VW mechanics - they've certainly helped me out a few times. I'm not affiliated with the site just a member.

Yes I have cleaned the Throttle Body twice and each time taking great care to clean it meticulously. When I restart the engine it runs smooth but after a few miles when its warmed up to operating temperature the Engine idles poorly and shakes very badly.
We find it best to keep an open mind to other peoples suggestions, until we find the exact fault. But, from your answers you seem to have everything covered.

Good luck with it
try changing the coolant temperature sensor, not much money and one of the few items that does not flag a fault code when it plays up.
This is generally the culprit when an engine runs ok cold and lumpy when hot.
Hi All

Will certainly try the temperature sensor, is this the one located at the bottom of the Radiator?

also another puzzling thing i noticed was that the car shakes when on an upward incline!

The only one I could find was at the bottom of the radiator. When car was shaking I took the wired connector off to see if it did make a difference but no nothing happened. car still continued to shake. Is it worthwhile replacing this sensor if disconnecting it made no difference? Many thanks.
The car is shaking when pulling uphill? That indicates a misfire under load, which is a different kettle of fish entirely.
Have you replaced the spark plugs, and if its an external ignition coil, run the car in the dark, looking for tracking sparks.
For grumpy idles, its often the throttle body at the end of the day.
John :)

Spark Plugs and Leads have been replaced. Car is lumpy when parked on an incline without even driving up it.
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