My 2.6 Cab's playing up.

[andrewaudi]

It's not idling right, it's revving up to about 1500 every second, then drops off a bit and back again. Anyone had this? Is it what I hope it is an just a sensor?

[scotty33]

Hi,

Could be a few things, is it temperature related, is it thirstier than usual?

Have you had the battery disconnected?

Have a look at reading fault codes, probably best place to start: (not sure what year the cab is, later ones will be OBD2 interface which is different - i.e 16 pin)

http://www.12v.org/maintenance/dtc.php?mil=no

likely suspects could be coolant temp sender or lambda sensors

http://www.12v.org/maintenance/repairs/ect.php
http://www.12v.org/maintenance/repairs/o2sens.php

There is also the possibility of a vacuum leak.

http://www.12v.org/maintenance/index.php?section=tr&ss=vac&auto=no&egr=no

I think it might help if the insides of the throttle body, were cleaned out with carb cleaner,
it is common for the intake hose to not seal well where it joins the throttle body, so worth checking this area anyway!

http://www.12v.org/engine/index.php?section=cl&view=rear

[andrewaudi]

It definitely will check the codes, never knew you could do that! It definitely has a sound of dodgy sensor about it with the way it's blipping up and down.

If I check the codes and it is an oxygen sensor, how do i go about getting the tool to remove it? There's talk of a 'Oxygen Sensor Socket', is that a standard socket or is it something I'm going to have to get from Audi?

[andrewaudi]

Oh, and for the past few days (before the idle went haywire), it's been drinking very badly. Was kinda surprised at how often I have gone to the pumps, my last tank I put in some Super as well... Not sure if that would have helped really....

[andrewaudi]

Actually, just read that properly, mines is a 98, so there's a good chance it's one of the later ones you are talking about :-(

[andrewaudi]

Ok, decided to take a proper look there based on that website, but it's too late at night to mess around with trying to get codes (it's not 16 pin, it's the same as the 12v.org plugs).

It revs up to around 1500 as if the accelerator's stuck, but I checked the cable and there's no obstruction, it dips and revs repeatedly by about 1-200 rpm every second or two, which makes me think it's the ECU doing the revving. It's exactly the same as me stabbing the pedal every second. The acceleration seems fine, but it's very jumpy when you take the foot off the gas and put it back on again. Even at idle, as soon as you tap the pedal the revs go way up.

I tried to disconnect the battery for a minute and then put it back on with no difference at all. I'm guessing it's normal for these cars to have no engine light anyway, cause mine doesn't appear to. Is the resistor necessary on the 12v.org site for the MIL? I got LED's and wires, but no resistors.

[andrewaudi]

Ok, I tried today to get codes from it, but the best I could get was a solid light, followed the destructions on the site, no joy at all. I'm going to just take it to a vag garage and get it sorted :-(

[scotty33]

Hi,

Based on the fuel usage and the idle problem, I'd guess it is a temp sender or lambda probe problem. Both can be faulty, but NOT trigger a fault code. A code is only triggered if the sensor is shorted or open circuit, it can be out of spec and cause rough running but not be 'failed' enough to trigger a code. Before you part with your money I would suggest you meter the temp sender and lambda probes as per the 2nd and 3rd links.
I use a ring spanner to get the lambda sensors out, bear in mind the old one will be faulty so it can be easier to just cut the wiring off and use a normal socket if you prefer. Use anti seize paste on the threads of the new one - somebody will be pleased you did next time it gets changed

[andrewaudi]

Throttle Bodies have been mentioned by my garage :-( They want 700 odd to replace it....

Anyone heard of this company?

http://www.motodyne.com/frames/12vsc.html

They appear to have cheap performance throttle bodies :-)

[andrewaudi]

I had a look today, is there anything in particular I should be looking for on the throttle body? I had a look at and couldn't see anything wrong, when I pull on the accelerator cable, it's pulling both valves open, one slightly after the other, they don't appear to be jammed or affected by anything, and besides from some oil, there's nothing else in there?

I had a look for the idle control valve, but can't see anything in the form of what's on the 12v.org website, but there are a couple of other doohickeys in there that look like it. I'll upload a photo later, anyone got any idea what it would look like on a 98? I'm guessing it's the one right in the middle of the first photo (under the wire) but don't have a scooby!

I'm starting to think it's the control valve because it seems to be running fine when I'm driving, just when it's idling and when I sink the clutch does it rev up.

What would it behave like if the valve was jammed open? Would it only be rough at low revs? It has always taken a long time to settle when cold...

[scotty33]

Throttle Bodies have been mentioned by my garage :-( They want 700 odd to replace it....

Anyone heard of this company?

http://www.motodyne.com/frames/12vsc.html

They appear to have cheap performance throttle bodies :-)

Yes,

They took money off customers for their supercharger kits then failed to come up with the goods. Maybe they are ok now, but being on the wrong side of the pond what could you do about it.

If your garage wants to replace the throttle body, I would find another garage! It might make an improvement, but only because it is clean inside.
My point with cleaning these out, is that a coating of grime on the insides of the t/b makes next to no difference to Peak airflow at wide open throttle, but at idle, the one throttle is fully closed and the primary is only slightly 'cracked open' this grime can then affect the airflow to a much greater extent. The ISV ends up trying to cope with a situation outside it's working range.
For same reason a duff temp sender/lambda sensor can make it run far too rich. This has less of an effect at higher revs but at idle, the extra fuel is too much for the isv to cope with. As you have raised fuel consumption, it is less likely to be a throttle body problem.
It is possible the throttle position sensor needs to be aligned, this can be done with vag com, there is also a diy method in this thread which may help?:

http://www.vwaudiforum.co.uk/forum/showthread.php?t=34879&highlight=throttle

[andrewaudi]

I'm going to strip it off tomorrow and give it a good clean, one other point I keep forgetting is that my battery is guff. I kind of figured that as long as it started the car that shouldn't make any difference to the running? Am I missing something else crucial here?

[andrewaudi]

Just re-read what that dude had written, and going by his guff battery trouble and the fact that his bother sounds exactly the same as mine, I'll get the thing started tomorrow, go buy a new battery and replace it, then try that ECU reset. Going by the pictures I sent (of the large valve), do you think a cleaning would really be in order? I don't want to go stripping off and destroying gaskets to clean the throttle if all I got to do is pop a fuse for a few mins! :-D

[scotty33]

As you say, pulling the fuses costs nothing, and I guess you'll be needing a new battery either way...
It does look like the smaller primary throttle is quite caked, imo the important bit to get clean is the edge of the throttle disc and the insides of the venturi alongside the closed throttle disc. I think you could do this ok with some oven cleaner and cotton buds or maybe a small toothbrush? Some people just blast carb cleaner into the throttle with the engine running, either way, no real need to dismantle if you don't want to?

[andrewaudi]

It was pretty painless to get to it (except when I touched the head by accident after a 20 mile trip). I'll grab and old tooth brush and I'm sure I got some carb cleaner kicking around, what's the worst that could happen? :-)

[andrewaudi]

Took off my idle control valve (i think) part number APM 078 133 455D. I had a look at this site: http://www.ms-motor-service.com/ximages/pg_si_0055_en_web.pdf they recommend for fitting back in that you move the adjusting cone, well I tried that and it took a fair amount of force to get any movement at all from it... Eventually got it out, but should it have taken a good deal to move it? seems to me like it should be a bit freeer....

[andrewaudi]

Hooray! After a few hours tinkering, some shouting and some worry, the thing is finally idling properly again!

Looks like that valve was to blame after all. On the valve it has 'Made in USA'.... Anyway, Audi want 140 to replace it, might shop around first, but I stuffed it full of WD40, emptied it and the gunk that was in there, then filled it up with grease, and it's a happy chappy again. For now...

MEGA thanks for saving me 700 quid, and only costing me a couple of days embarrassment at the lights :-) Oh, note about the fuel economy that I mentioned before, I think it's probably just ***** on this car anyway :-D

During all my tinkering I had the battery disconnected and fuses out, so now it seems a little rougher than before at idle, is what I have read about the ECU needing to 'learn' the engine again true or is that rubbish? Should I expect it to smooth out?

[scotty33]

Nice to see a problem solved with persistence!:beerchug:

re the ECU, when you cut power to it it defaults to factory settings, as you drive the car, the ECU may start 'fine tuning' some of these settings to run better with the 10 year old engine and sensors.
The throttle body alignment seems to be one of the settings that is lost with a power cut. Following the link procedure set down by user name 'Vampire' may help restore things quicker, if you have not done it already?

[andrewaudi]

Have done that when I stuck the valve back on, had fuses all over the place and the battery out for about half an hour.

I have to admit that at first it was running rough (probably chocking on some of the carb cleaner still kicking about), but since then it's now running smoother than ever, the idle is lower than before and when warming up it's going much better, so I suspect that the valve was already a bit knackered! This improvement may be to do with cleaning the Throttle body valves out also...

Seems strange that such a good car would have so much bother with running out of battery? Anyway, I'm happy, and grateful for the help!