Hi all, hope someone can help with this.

Have got an Octavia 90bhp TDi, 210,000 miles, doesn't use oil between regular services, still does 50+ mpg and can still touch 100mph! That's the good news!

However, when idling, it intermittently feels like it's dropping down to three cylinders and only a quick blip on the throttle clears it for a bit. It will clear itself for anything between 5 seconds and a minute, then it comes back again. It is worse when the engine isn't at full operating temperature.

It's more annoying than anything else because it makes the whole car shake!

It's actually been like this for about 90,000 miles, a lot of mechanics are baffled, nothing comes up on diagnostics, i've already replaced the EGR valve and driven without the MAF sensor connected(to test it), but nothing so far makes a difference.

Any ideas anyone?

Cheers

Stu

It runs like it's got a misfire? About the only things I can think of that would cause that are a bad injector, or an intermittent failure in the electrical signal to fire that injector.

When was the last time you clean your EGR Intake Manifold???

They get very dirty inside with carbon deposits and MAYBE this is causing your rough idle.

Do a Internet search for VW EGR Cleaning or VW Intake cleaning you will find a lot of info on this matter includiong pics that will show you how dirty they can become.

http://pics2.tdiclub.com/gwillie/VW/Sballintake/Intake_Manifold_Cleaning.pdf

Also check the forum www.tdiclub.com they talk only about VW TDI engines.

Good luck,

Isaac

Coolant temp sensor perhaps? Normally they seem to make it rev high but you never know. Have you had it checked for error codes?

Could be relay 109. These can cause all sorts of problems when they go faulty. The original white ones are unreliable and have been revised (grey ones).

Thanks for all the replies,

Already had the Relay 109 problem about 18months ago, in my case the engine cut out completely and had to be towed

Car doesn't show any error codes

Had a look at 'Turbo Boss's link and had a word with my mechanic who fitted the new EGR valve, he managed to clean the intake manifold but only with it in situ, so my guess is that probably needs to come off and be cleaned properly as there's bound to be some nasties in there! Plus it's probably the next cheapest option before I start getting into looking at injectors.

Thanks once again, will post up what happens!

Stu.

You cannot clean the intake manifold and ports with it in situ, period. It's a messy and time consuming job off the vehicle.

Check the case pressure relief valve on the IP body, it will probably have fallen apart and need pressing together.

Get a full fault code scan and post it back.

If on original injectors, get a new set of nozzles and 2 stage pop testing done on them (genuine bosch nozzles, not chinese ones).

A decent VAG mechanic will be familiar with all of the above.

Greg.

Thanks for all the replies,

Already had the Relay 109 problem about 18months ago, in my case the engine cut out completely and had to be towed

Car doesn't show any error codes

Had a look at 'Turbo Boss's link and had a word with my mechanic who fitted the new EGR valve, he managed to clean the intake manifold but only with it in situ, so my guess is that probably needs to come off and be cleaned properly as there's bound to be some nasties in there! Plus it's probably the next cheapest option before I start getting into looking at injectors.

Thanks once again, will post up what happens!

Stu.