115 Tdi Surging At Idle

[adie_morris]

Hi all.

I have been a member here for some years, however for some reason my other account will not allow me to post!

 

I have a 115 Tdi 2002. Have done a lot of work to her over the last few weeks.

 

Firstly, I finally got around to doing the glow plug in the aux heater.....then had hastle with leaking coolant pipes, but sorted now :rolleyes:

Then I did cambelt (kit) & water pump, was about due again at 117k

Full service (apart from pollen filter, did that last time, hate that job!)

O/S Track rod end changed

N/S outer CV Boot.

Changed the Bracket securing intercooler pipe under crank pulley, found to be cracked!

New Rr Shocks.

 

That was all a month ago.

No probs until today.

Car is driving lovely, however when my wife pulled up at some traffic lights today, she noticed that the idle speed was up and down like a yo yo.

Take the revs up slightly and runs fine again.

As I was at work and couldn't get home & she was panicing she wouldn't get home, we called RAC, he didn't know what was wrong but said it was safe to drive.

I got home from work and started her up. I then worked out that the surging idle speed only happened when there was a load applied , i.e. a/c comes on or all lights switched on. Switch all auxilliaries off & she's sweet as a nut!

I am now starting to wonder if it's alternator related or MAF.

I got my VAG COM out and a quick code check revealed... Nowt! all fine.

Next I removed plug from MAF and immediately noticed the surging stopped!

I gave a good blast of the throttle and re-connected MAF.

Cleared the fault code that had now been generated & to my suprise it now seems ok!

 

It is early days yet & I expect the fault to re-appear but was wondering if anyone else had knowledge of anything similar.

A strange fault that should only occur at idle & only under load but otherwise drive fine.

 

I should also say that today was a very hot day about 25c, so a/c had been working hard, but saying that even with that off and just headlights on it was surging.

Am hoping to drive to seaside on sunday, good 2 hr run, that will be a test.

 

Any help or advice appreciated.

 

Thanks

 

Ade

[gregers]

im wondering as you say if it just needs a bloody good run,perhaps if you can do an Italian tune up and give it a chance to burn any crud off?

[adie_morris]

Cheers gregers,

 

Another 24 hrs and still seems ok, although not been far in it today.

 

Tomorrow is the big test, north wales, that should warm her up nicely ;)

[adie_morris]

***********UPDATE************

 

Well, had a 200 mile drive yesterday & I really didn't hold back!

 

As you'll see on my previous post, I had no probs at all on Saturday, so I was hopefull it was cured.

 

She started surging again before I had even finished getting the kids in the car!

 

So I gave her some real stick all the way to North Wales & back .

 

One thing I noticed, was you could slightly feel the surge when driving at low revs in a high gear, say 40 - 45mph in 6th.

 

Anyway, by the time we got home she was running right as rain again!

 

& today?

 

Not faulted again!

 

So, the jury is still out as to whether or not she is cured!

 

I have a couple of thoughts as to what it may be, see if you agree.

 

1. Possible Alternator, unstable voltage at low speed ........need to get voltmeter on it next time playing up.

 

2. Possible MAP sensor, this senses the vaccum in the manifold, higher the reading the more load is being placed on engine, signal to ECU, more power please..(I simplify!) if giving false readings, VAG com job.

 

3. Split Vacuum pipe, I don't really think so because it is intermittent.

 

4. EGR valve, possibly sticking open, should be closed at idle, else it will choke the engine with exhasut gas.

 

5. MAF, but still doubting this one as there are no fault codes present.

 

Anything else ??

 

Ade

[chrispb123456]

Hi Ade

A couple of years ago I had an intermittant loss of power, which I decided to get a MAF sensor from ebay, it cured the loss of power but tick over became very erratic, was continually speeding up and slowing down on it own.

In the end I paid

[adie_morris]

Hi Ade

A couple of years ago I had an intermittant loss of power, which I decided to get a MAF sensor from ebay, it cured the loss of power but tick over became very erratic, was continually speeding up and slowing down on it own.

In the end I paid £65 for a genuine bosch unit and have not had the problem again, seems the Ebay ones are cheap copies (no Bosch markings)

Thanks for that Chris,

 

The same thought had crossed my mind, but the dilema is, do I go out on a whim and put one on it, as there are no fault codes!

It does still have the original one on it, pretty good going 118k and 8 years old.

I was having a good look at her yesterday and it seemed no matter what I unplugged, it stopped the surging!

For example, I unplugged air flow meter, run sweet, plug back in, rough!

Unplugged Map sensor, run sweet, plug back in, rough!

Then just as I went to clear the new fault codes I'd created she ran sweet again & didn't play up at all after that :(

 

I also managed to get voltmeter on her when she was surging and can rule alternator out as that was remaining stable.

 

Did you have fault code showing when you replaced yours Chris?

 

Ade

Edited July 1, 2010 by adie_morris

[chrispb123456]

Hi Ade

 

It's quite a while now since I changed it, well before I had vag com.

I had been talking to the guy at the mot station and he said had I had any problems with the maf sensor, as they were prone to problems with low power and running rough.

It was a few months after that I had occasional problems as above, thats when I got the ebay special which sort of cleared the power problem but got this surging tick over, went to my local spares shop, he got me a genuine Bosch exchange unit.

I didn't unplug anything and try running it at the time so cant comment on that.

 

Chris

[mk2vr6]

unless its a complete failure the maf wont bring up a code, the system adapts to allow for the gradual degradation of the sensor till it gets beyond the acceptable parameters

[adie_morris]

unless its a complete failure the maf wont bring up a code, the system adapts to allow for the gradual degradation of the sensor till it gets beyond the acceptable parameters

Thanks for that.

Hopefully this could be the answer then.

I shall change the MAF next & report back on findings!

Having said that she has run fine again today! :unsure:

[Jayton]

How much surging?

 

I noticed with the AC on mine goes up and down slightly, maybe +-50rpm either way. Turn AC off and it doesn't do it.

[adie_morris]

How much surging?

 

I noticed with the AC on mine goes up and down slightly, maybe +-50rpm either way. Turn AC off and it doesn't do it.

 

Mine doing about +- 200 rpm, but intermitent and not just if the air con is on, if ac is off and switch lights on it does same.

 

Don't think it's anything to do with electrical load though as voltmeter test was ok and you can also feel it slightly if you are on a flat road doing 40mph in 6th (engine speed near idle). any slight increase on accelerator and fine.

 

It's the intermittent bit thats such a pain!

 

Not played up today either ;)

 

MAF sensor going on her next time she throws a wobbly! (sounds like the wife! although MAF sensor won't cure that one!)