VW Golf cutting out when you slow down

Forgot to ask:

I read somewhere that the "main ECU relay" is likely to be the problem. What is that, and could it apply in my case?

Thanks again, Constantinos

Constantinos ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :

N's 95-6. Which would make it a Mk 3.

Sorry my mistake. I think it's 96.

I've seen several posts about Golfs having the same exact problem: engine cuts out as you slow down (e.g. at a T-junction). We took my wife's car (N-reg i.e. 1997-8, petrol, 1.4? not sure) to a VW dealer who did diagnostics and came up with 3 things that "have to be done":

- Lambda sensor needs replacing, and that's probably the root of the problem

Lambda sensor does not have the capability to cause stalling,- only +/-15% mixture trim.. If MPG is abit low and it fails on emissions test, the sensor is likely kaput though.

- Throttle body needs clean, and he said it might need to be replaced.

On this yr of 1.4 the throttle body is just that. A body. No built in throttle motor or anything. However it could be a gummed injector (common) or a faulty stepper motor (fairly common also) Yes it should be spotlessly clean inside, and the stepper motor cleaned and lightly oiled, likewise the throttle linkage.

- Pre-heat pipe (?) also needs fixing.

Yes, fix that, but wont cause stalling.

Intake vacuum leak is also a strong possibilty. What the idle quality and speed like when it does manage to sustain an idle??

Tim..

Does it start immediately and idle? Does the idle occasionally wander all over the place?

Tim - many thanks for the reply.

I'm not too sure what you mean by idle quality and speed, but when I drove it the other day I don't remember it shaking or anything like that. What should I be looking for?

Constantinos

No problems re-starting it. I didn't notice if the idle wandered, will have a look tonight when I pick it up from the dealership - I'll take it somewhere else (recommended place) where they can do the cleaning for less.

If the idle wanders around a bit then the stepper motor (idle actuator) is at fault.

Many thanks, I'll check that out.

See if these two help you to decide if you want to go ahead cleaning the throttle body yourself: If you can change a 3-pin plug, you should have no difficulty DIY. What you need is understanding what you are doing, and patience.

Cleaning the Throttle Body

Thanks Lin, I have to be honest here and say that I've never even changed a 3-pin plug....... {embarrassment}. I can't help but think that if I try to clean the throttle body myself I'm bound to break something else.

But the place I'm taking in to tomorrow (Hi-Q) sounds good - only =A325 to do the cleanup. Not surprising that the VW dealership would charge 4 times as much for their time. Well they're not getting it from me.

Ok, the idle does occasionally wander, but not much i.e. between 600 and 800rpm. There's some slight shuddering, but nothing that I would consider out of the ordinary. Would this still be the stepper motor/idle actuator?

Thank you all btw, this has been a great help.

The 8 valve 60bhp 1.4 is usually a very smooth operator and unless its very minimal the idle should be rock solid at ~800rpm.

Sounds like it needs a good going over.

Tim...

I would say from your symptoms - yes. Had a Pug 405 that did exactly the same. New stepper motor - About £80 plus VAT OUCH! - sorted the problem and took about five minutes to fit.

Mechanic called me, said they cleaned up the throttle body, sparks etc. and the car's now running a lot better, not cutting out, revs are higher and stable... sounds good! But he also said that the rotor belt needs replacing otherwise the problem might return soon. =A315 to replace it sounds like peanuts and they can do it today - I said go ahead. Asked him about the stepper motor/idle actuator but he didn't think it was that... so I guess I'll pick it up today and see how it goes.

Just for the record: it was actually rotor arm, not rotor belt. Anyway I picked up the car and so far so good, it's handling a lot better and not once even seemed to be starting to cut out. Idle revs are stable at