Strange Idle problem

[TheMadhatter]

Over the last few months my 130 TDi sport has developed a strange idle problem when cold. It had got so frequent that I took it to the garage the other day. However there where no fault codes and the bugger did not "perform" for the mechanic.

The problem is as follows.

The problem happens when the engine is cold, that is less than 15mins of driving. As I come to a stop at a set of traffic lights and I have the clutch pushed all the way down the engine seems to miss a beat and the rpm drops 100-200rpm. Its a very pronounced shudder that you can feel through the car. It is only last 1sec or less. Once the car is warmed up it stops doing it. I can sit and let the engine idle, rev it ect and it wont do it. The harder you come to a stop the more pronounced it is.

Any ideas whats going on ?

At the moment I am reduced to waiting for something to break or show a fault.

[Sam]

Sounds like a vacuum leak, inspect the vacuum hoses around the manifold area.

Could also be a failing MAF but start with the free stuff first.

[TheMadhatter]

Thanks I will check them out when it stops raining. I found that I can simulate the fault by very quickly lifting the clutch up and down with the car in gear and stationary.

[gtime]

Funny enough sounds similar to a problem I'm having the my tiguan r line, once warm it's fine but leave it for 20 mins or so, start the car and within minutes idling and juddering through whole car, smells really sweet out of exhaust. As you say once warm it's generally ok. It's back at the dealer Tuesday as only picked it up Friday so will let you know outcome. Same no fault codes though

[TheMadhatter]

This one makes no sense to me.

It would seem that throttle position, how long it idles for have no effect. Its the act of coming to a stop that causes the engine to hicup. It always happens immediately after it comes to a stop. If it was a loose wire/connection/hose I would expect it to still do it after the engine has warmed up.

For example on the way home tonight I saw that the lights 100m ahead had turned red so I pushed the clutch all the way down and coasted to the lights braking smoothly as I could. Immediately after the car had stopped it hiccuped.

Gonna have a poke around as soon as I get a chance and see if wiggling anything can reproduce the symptoms at idle.

[TheMadhatter]

I checked everything thing I could see. One of the vacuum hoses was a little loose, horrah I thought and then DOH ! as it carried on doing it after I had sorted it.

Could not make it do it by wiggling wires and vacuum hoses so I think the only thing to do is wait until something breaks.

That puts both me and the VW specialist at a loss.

I suppose the only way of finding out would to have the engine logged as it drives around ?

[Sam]

If you have access to a MAF you know isn't faulty, you could swap and see if it goes away, but that's a long shot.

If you've got access to VCDS then yup, logging would assist.

Is the specialist using VCDS or a generic OBD scanner?

[TheMadhatter]

Thanks



Is the specialist using VCDS or a generic OBD scanner (http://www.amazon.co.uk/dp/B00EQ1U8BA/)?

Not entirely sure but he can log the cars telemetry as it is driving round so it sounds like it.

[martin1810]

Does it only occur when the brake pedal is touched?

[Crasher]

The first thing I would do is fit a new in head injector harness.

[TheMadhatter]

Does it only occur when the brake pedal is touched?

It only seems to happen when the brake pedal is depressed, but then it is happening when the car stops. Pushing down on the brake pedal at idle or when driving does not make it happen.

I found that the thermostat had failed and that has been replaced.

After watching it a few weeks I have come to the conclusion that it is definitely engine temperature related. By that I mean the following.

If I get in the car and drive 400m and stop at the first junction it does not do it. 1km further on at a set of traffic lights and it does it. By the time the coolant temprature is 3/4 of the way to normal (90) it has stoped doing it. The rest of the time in never misses a beat.

[passat 130 tdi]

take the pipe off the egr and blank it off , then try the car again

[martin1810]

Use vcds to log coolant and fuel temperatures. Fuel temp sensor may be reading wrong.