Revs dropping/possible stalling...oh noes!

[dougmcdonald]

Hi there,

I was hoping someone could give me a bit of advice on a problem I've recently been getting on my my cupra.

Basically, as of a couple of days ago, from time to time, when idling, the revs seem to drop from it's usual 800 or so, down to 500-600 and the car feels like it's going to stall. This is in neutral not doing anything.

When driving normally and above 2k revs things seem fine, but when coming to a stop in a queue or junction etc and taking it out of gear when the revs would drop back down below 1k it is occasionaly doing the same thing, revs dropping lower and lower and feeling like it's going to stall unless I put some revs through it.

I'm a bit new to the terminologies used in the troubleshooting guides, so I apologise if this is an exact description of a common problem, if so could someone point me at the right section in the common problems section.

As additional background it's due in for a service in 2 weeks so I'm wondering whether I need to do something asap, or just wait and mention it then?

Any info would be a big help,

Many thanks,

Doug

 

[LEE69]

Might be an air leak?

 

[dougmcdonald]

Would there be an easy way I could check for an air leak? Rubbing the hoses with flour or something! (ok perhaps not the greatest of plans!)

Or would that be something best checked at the garage? do you reckon?

 

[traumapat]

So its only affecting idle? once driving its fine?

 

[LEE69]

You can use carb cleaner or wd 40 spray around the inlet and hoses and when the revs rise, bingo

Look for split hoses visually too.

 

[dougmcdonald]

I will have a look for split hoses at lunch (before it's dark!)

I do have some wd40 sitting at home, what should I be looking for specifically with respect to that? dry spots where air has blown the wd40 off?

It seems to 'mainly' occur when idle, but if I say drive 1st > 2nd with a change at say 2.5k revs and then the guy in front brakes and I can't put revs through it straight away I can get the juddering/almost stalling when both moving and in gear too

 

[LEE69]

If it sucks it in the revs rise.

 

[Rocky Rocastle]

Lambda sensor if it's under fueling and rough idle?? Im not the most knowledgable tech on here by any stretch but just going of experience.

 

[cupraslayer]

Mine used to fo that. Reset my throttle body and problem solved. Only takes 5 mins and doesn't cost nothing. Worth a try to see if it's the same.

 

[LEE69]

It does, you need vag com

 

[dougmcdonald]

Ok, slight update, I had a check about and can't see any obvious physical damage, split cables etc

Throttle body reset is certainly worth a shout, unfortunately I've not got a VAGCOM
I will certainly ask if the garage can check it out and run the suggestions here too, (throttle body and or lambda)

Last this I suppose it to ask, am I going to be doing any serious damage by continuing to drive it when like this? I've always hated that 'I'm just about to stall!' feeling in any car under the assumption I'm breaking something!
If I ensure I've got 1500+ revs at all times should I be ok to keep it going for the next two weeks to the service?

 

[LEE69]

Ask in the vagcom section if anyone is local to you, it's a 2 minute job.

The pipes can be split anywhere, overtightened clip can do it to.

Did you try a spray?

 

[dougmcdonald]

I will do that Lee, thanks for the pointer

I'm afraid I didn't WD40 things yet, I'm afraid this stems from realising after I got home that I didn't really know where I needed to spray, I kind of though it would be obvious, but to a lamen, I was a bit out of my depth and didn't want to go spraying about inside the bonnet on the wrong thing!

Are there any 'basic' instructions on what I should spray (as in location/diagram or something) I'm afraid I'm very green when it comes to anything further forward than the steering wheel!

The only other thing to mention is that I did change the temperature sensor to a green cap one the other day (which incedentally doesn't seem to have fixed my fluctuating temperature!) and I did wonder whether I had fitted it back in properly and if that could cause anything like this, I'd be surprised, but just thought I'd throw it out there.

 

[LEE69]

Anywhere there is a rubber hose basically, under the inlet is a favourite for them to go but you will see an oily residue over the pipes if that was the case.

My moneys on a thermostat then, this colder weather really shows them up if there is a problem.

 

[dougmcdonald]

Ah ok, I will do that when I get home and see if I can notice anything odd. Thanks again

Yeah I'm thinking the thermostat is due for a replacement, I will certainly get that done at the service. Are you suggesting that the thermostat might be the cause of of the rev issue too? or was that a seperate comment?

 

[LEE69]

No, a separate comment.

 

[dougmcdonald]

Thought so, just checking

 

[cupratune]

Did you find a cure? Mines doing the same thing at the 2k mark in 1st/2nd
Guessing the screw missing from the air box might not help, guessing previous owner didnt fit it back on.

 

[LEE69]

Guessing the screw missing from the air box might not help, guessing previous owner didnt fit it back on.

Holding the cover down?

Won't make any difference the air is metered.

 

[dougmcdonald]

I've not yet found a cure no, I've got a warranty for another 1500 miles/6 weeks and I'm having it serviced on the 2nd and will let you know what they find.

I phoned the warranty garage out of curiosity to see what the terms were for charging bits back to them and the guy there reckoned it would be something in the cold start system, probably the airflow meter or similar (which to be fair he said if it was I didn't need to come back to them, just get it done)

I'm due to phone the garage I'm taking it to for the service in the next day or two to tell them what to look for, so I will mention that and see what they say.

It's very inconsistent my issue, today for example I drove the 15 miles to work without it happening, but on the way home yesterday on the same journey it did it on 4 seperate occasions.
It also doesn't always happen at certain revs, it just 'tends to!' by which I mean I can turn it on, and it will be fine, drive the 500 yards to the end of my road, disengage the clutch and then it will do it. It doesn't seem to be related to the car being physically cold or hot, purely when the revs drop below about 1500 or so

The concerning bit is that the other day on the way home I pulled up at a roundabout and it starting chugging away as described, so i put some revs through it and it stopped juddering....fine I though....until I tried to pull away and I got absolutely no power, I started rolling forward into the roundabout but my throttle did nothing! I started gently pumping the throttle rather than just pressing it and it did pick up eventially, but only at significantly higher revs, felt like a massive dead spot from about 500-2000 revs on that occasion.
Either way it's certainly not good, so I'm driving it as little as possible before I can get it to a garage.