Golf Mk3 erratic idling

[MysticMartin]

I’ve seen similar idling problems on this forum but they haven’t been able to help me, so hopefully someone can suggest something specific to mine.

I have been having trouble with the idling on my Golf Mk3 since I left it for a week whilst on holiday.
It was a cold night when I got back and started it. It spluttered so I pressed the accelerator but when I let go the revs stayed at about 2500rpm. I turned off the engine and started it again and it was better but for 3 weeks now the idling is high and varies up and down between 1000 and 1500. This happens even when fully warmed up. Also it causes the car to kangaroo when I’m going at a steady speed e.g. driving along at 30 where I’m hardly touching the accelerator it will suddenly lose power and then regain it.

I’ve had a look at the throttle unit, cleaned it all up and believe it’s working. When starting from cold the butterfly valve opens slightly via the servo but the revs go up and down without the butterfly valve moving. So I’m pretty sure it’s revving because the fuel is being varied not the air intake.

I suspected it might be the Lambda sensor. I’ve got a bit confused here. I tried buying a 2nd hand one on eBay and it made no difference, but when I measure the voltage coming from them both it was steady around 0.5V (but I’ve read it should vary between 0.1V and 1.0V) which suggests both sensors are faulty. I don’t want to spend £60 on a brand new one just on a hunch.
I also bought a VAG cable and plugged it into a laptop, but the engine says there are no fault codes.

I couldn’t see any leaky hoses, but saying that I didn’t look underneath the big black unit that passes the air to the engine. Do I need to take this off and check?

Hope someone can suggest a miracle cure!
Thanks
Martin

[SammoVWT]

Do you know what type of engine it is? Size/Year/Block code - there are a ton of variants for mk3's

It sounds like a throttle body issue - ive had similar symptoms recently, but managed to clear them after a code scan and a throttle body re-adaption.

I think it might be 00516 throttle position sensor improbable (from memory) - something like that anyway, was one of the issues i got on my scan after clearing the faults, but after a clear and reset it dissapeared

I would just make sure nothing is loose on your throttle body, its under the airbox - depends how ready you are to get stuck in to how much you can do yourself

Edit: Also just read your lambda sensor post, dont forget the lambdas will osscilate from 0.1 - 1.0v as it keeps modulating the fuel, so depending on your meter you may well be seeing an average, also you should be careful measuring the voltage on them, they are pretty sensitive and trying to measure certain things can damage them

[MysticMartin]

Hi Sammo,
Thanks for the reply.
My Golf is 1997, 1.6 model CL, and the engine is an AEE.

When you say "code scan" is that with a VAG? I couldn't get my VAG to show any errors.

I don't think it is the throttle position sensor that's the problem because the butterfly valve is steady. I suspect it's more likely to be the pipe-work underneath the throttle body. I have taken the throttle position sensor unit right off but I haven't taken off the big black plastic unit underneath the throttle unit.

Thanks for the tip with the lambda sensor. I read somewhere that you need to use a digital multimeter to avoid damaging them; luckily I read that before trying it!

Martin

[SammoVWT]

Hi there, yeah with vag-com, the trouble is without knowing the engine model its hard to get an 'accurate' forecast, thats one thing that is pretty important to get the right help.

My tb was acting in the same manner as yours, but depending on the engine depends on the fix you need luckily, mine is a 1.6 AEE (same year same car!) so i know what im looking at now.

Theres a black braided hose ontop of the throttle body, take it off and make sure its not split or perished. This is your vacuum line for your idle control etc. (while you are there, there is a black rubber hose which connects to the airbox, which is your breather hose. Make sure its clean [and the filter] as they are prone to gunging up with moisure if taken on a lot of short trips where the car cant warm up - dont think its related too much to your problem, but worth doing all the same. Dont put any liquids down it whatever you do, just use something you can shove down it to make sure its clear)

Also, if you unplugged the sockets with the car running, it will generate a fault. In the end doing that allowed me to reset the TB. The MAV has a couple of software bugs, where if the planets align right it will screw up. Not a major problem if you have a VAG-Com handy!

Definately try to do a re adaption - the block for the MAV system is 001 rather than 098 for most others. if you need a hand on how to do it gimme a shout

Also with the lambda, its always best buying a new one, something you cant really cheap out on. I had my car repaired recently, and the garage in question im 90% sure they put my parts on ebay, not just mine from what i read anyway. So be careful if youre buying used parts from ebay! Also vag com will measure the lambda voltage so you wont need to use a meter.

The also could be a cracked inlet manifold or a gasket gone under tb, but ive seen the exact same problem on my car. the TB on this model is a pain

[MysticMartin]

That's a handy coincidence about our cars!

Interesting what you say about the breather hose (between the engine and the air filter box) - it always clogs up with watery oil. I've already cleaned it though and it made no difference. Maybe this isn't the hose you were referring to.

I think I need a quick lesson with your acronyms:
Does TB = Throttle Body
What is MAV?

I was using address 01 on the VAG-COM to ready the engine. I was surprised to find it gave no errors even when I disconnected the lambda sensor.

I'm a bit confused where you say "Also, if you unplugged the sockets with the car running, it will generate a fault. In the end doing that allowed me to reset the TB". Which sockets do you mean?

Cheers for the other info about the pipes and inlet manifold. I'll have a play this evening.

[SammoVWT]

For the breather, thats just routine maintenance, thought it would be useful for you to do, if it gets blocked, oil will force its way out of any part of the engine it can because of the pressure build up. Basically bad for you car.

Theres a connector which links the throttle body to the ECU on top of the TB (Throttle body) itself. If you unplug that while the engine is running, see if the revs drop down to normalish idle level, it will be rough but will generate a fault in the ECU.

Since you have a cable you can reset it easily. When you are adapting 001 you should hear the TB modulate, its important to leave it for at least 30 seconds before unplugging and turning the engine on. The 4th block should read 00000000 when its complete.

The vacuum hose is a braided rubber hose on top of the throttle body, it connects to a brassy coloured metal tube on the top, and should slide right off with a bit of effort, you are looking for signs of a perished hose. You can try spraying some water on the outside of the hose while its connected, and see if any of it gets pulled in, if it does then your vacuum hose has perished and needs replacing.

Also the code scan for block 01 (engine) is different from the code for the TB settings, its in a different section of vag com. To do with the measuring blocks (and basic settings).

you cant miss it, its the only hose on the top of the construction. Give that a whirl, if thats all ok, and you cant hear any air leaks, then I would say its a safe bet its a software issue with the TB or the TB has failed.

Apparently TB failure is rare, and they are fairly robust. Have you tried running the car and putting some carb cleaner down the butterfly at around 2500 revs to stop it from stalling out?

Also, TB is throttle body yes, and MAV is the type of fuel system we have in our engines being a marelli one iirc. Hence why our adaption code is 001 rather than the bosch jobbies.

(there could be a few other issues which cause this, so if this doesnt work it may well be worth looking up on the symptoms, for example and airleak on the inlet manifold somewhere etc)

Also for what its worth, i think my TB played up because my battery was dying, see if you get 12V on the battery, and check when the alternator is running (appx 14V).

[MysticMartin]

Interestingly I read the fault codes again today and got an error - for the lambda sensor. I just hope it wasn't me probing it which caused it!
The error reads:
Control module part number: 032 906 030 N
component/version: MARELLI 1AV 2080
1 Fault
00525 - Oxygen sensor (G39)
07-10 - signal too low - Intermittent

I see what you mean about MAV = Marelli!
So do I rush out and buy a new sensor? Maybe this is an error from when I was testing it by disconnecting the sensor. They cost £60 or appraently new on eBay for £30.

Anyway, looking at you other suggestions...
The battery voltage is 12.5V and with the engine running 14V

I pulled off the braided hose and blew down it with my finger over the other end. It didn't hiss or leak so I guess it's in good shape.

I've already tried carb cleaner down the butterfly valve while running the engine.

I've been struggling to understand what you mean by "adapting" but I now realise it's part of VAG-COM. I got the VAG-COM software with the cable I bought on eBay but it's not registered so lots of the functions are disabled. I've just looked at the registering process and it costs $99, hmmm, more than I expected.

I'll carry on tinkering.

[MysticMartin]

An update.
The VAG-COM does give me more readouts than I thought. The lamda sensor is showing a varying voltage so I recon it's ok.

I tried disconnecting the TB cable after starting the engine for 30 seconds. As you said, the revs dropped off and the VAG-COM shows an error.

It's still got the problem though

[SammoVWT]

Well at least you confirmed that the TB is the problem so not a complete loss!

[MysticMartin]

Thanks for all your help so far. I'm having a go at your suggestion of:

"Since you have a cable you can reset it easily. When you are adapting 001 you should hear the TB modulate, its important to leave it for at least 30 seconds before unplugging and turning the engine on. The 4th block should read 00000000 when its complete. "

I'm still a tad confused how to do that.

Cheers