Erratic idle

[RobI]

I've got an 51 (32K mls) plate 1.4 petrol and it's idling is odd. It seems to suffer when coasting from 1st gear the worst where the idle drops to nearly stalling point (~600 RPM) before pushing back up to normal ~700. This occurs when the engine is at normal operating temp and is seemingly unaffected by ambient temperature. Once idling, it is not enitrely solid at ~700 either.

Perhaps related is the fact that when the engine is up to normal temperatue and the car is at idle, using the electric windows or moving the power steering causes the revs to drop quite considerably.

I've has the odd occasion where the idle bounces from 600-800 rpm really quite rapidly and it seemingly is cured by a dab of the throttle.

I've just has a service with the 'additions' of plugs and filter and it has made no difference. Battery looks OK (green on the indicator of the battery) but is now 5 yrs old. These are expensive though so reluctant to replace until required. Audi told me the leads 'never' need replacing which I find odd.

So far the car has not stalled (touch wood) but is a concern. Car drives fine otherwise i.e. no misfire.

All notes taken when the AC compressor is switched off.

Any help will be greatly appreciated!

 

[Beef]

I think we've got something similar on our 2003 A2, although not as extreme. It may be the throttle potentiometer.

I'm having ours VAG COM'd in the next week or so and then I'll report back.

In the meantime you could ring up an auto electricians - they may be able to help.

Cheers,


Beef

 

[audio]

any results on this thread? anybody?

 

[murran]

clean out the throttle body and reset the adaptions afterwards.
the throttle flap gets carbon deposites around it. too much to cope with for the ecu to work out why the throttle flap is having to be at 6/7degrees to maintain idle speed when it should be 3/4degrees.
it hunts up and down trying to find itself.
this is a little of an **** on an a2 as you have to put the stupid ill designed bonnet somewhere. why the **** they thought it was a good idea to have a removable bonnet??? maybe audi did a customer survey on they're prespective customers and discovered the customers would be hamsters.... who could easily store the bonnet in the side of their cheek while they worked on the engine????
or probably more predictably audi wanted to put off their customers from removing it at all!
rant over!

 

[audio]

Done the throttle body clean up using aerosol spray (wynn's carb cleaner) without opening up the part n cleaning it. Would this spray give enough cleaning inside? please comment . A2's 1.4Engine is more lively and sporty now and responds to accelerator quicker than before cleaning the throttle body. the idle revs have gone down though, does that pertain to your advice 'to reset the adaptions' ? how to do that?

 

[murran]

without diagnostics i dont think its possible to reset the adaptions. its should re-learn over time now anyway, now youve partially cleaned it.
i would advise removing it to clean it as most of the carbon crap will be under the throttle flap. plus you dont want what you cleaning off going into the inlet manifold.

 

[audio]

Thanks murran, the rough idle wasnt totally cured so i decided to remove the throttle body parts and clean it shiny with all bolts, gaskets and o-ring replaced with new ones from audi. the area under the butterfly was indeed full of carbon crap and the gaskets were very much black and worn down. also removed the recirculation valve and checked the gaskets, replacing anyway. Now the car is sitting in my garage waiting for parts (i.e. bolts and gaskets) from audi and expected tmorw.

Also had a little issue with one of 2 slotted bolts (T15) on the butterfly itself which looked quite bad and it had no torx grooves to unscrew it (probably previous owner's DIY). i know that I could leave it just like that but i wanted it to be sorted to calm my OCD down. took me a while to actually extract it using 1.5mm drill bit and extractor bit. bigger problem is the the bolt comes as a part of throttle body hence doesnt have its indidual part code so nothin available from audi parts shop. On the look now to find if someone has a spare/salvage part i have however gotten hold 4x12mm slotted machine bolts (-) just in case if i dont find an exact match.

Read somewhere about disconnecting the battery to reset values, is it a part of reset procedure or a trick itself? Audi is charging 132quids for diagnostics/resets. I checked from another local garage and they quoted 30 for diagnostics and 20 for reset plus VAT. I was thinking about buying a 20quid software from ebay n try myself, what do you think? any recommendations?

Cheers

 

[murran]

just refit it. the ecu will re-learn after a good drive.
resetting the adaptions means it starts a fresh from factory settings. but after learning adaptions from being sooted up in carbon, and then cleaning it, from driving it afterwards the ecu will learn "the other way" too.

the garage i work for charges £39 for diagnostics read, inc 1/2 hour investigative time if needed to say whats wrong. if more time is needed to locate the fault we'd ring you and ask for authorisation to spend more chargable time investigating it.

 

[audio]

Refitted everything just nice with right torques although I had a little doubts on the EGR coz if the area under the butterfly was so full of gunk, i am not sure if EGR will be any different. isnt it so? and now I am getting engine management light off and on. Driving smooth and suddenly many lights turn on and car idle becomes quite erratic. Turn off the car and turn on to get a little stable idle but with the engine manegement light turned on. this light gets off sometimes but turns on again with same pattern.

I got VCDS from a garage nearby who charged 36quids for diagnostics and one more diagnostics check after 30 miles after 1st check. I got 5 faults that were found:
1. 17851 - Potentiometer for EGR (G212) P1443- 35-10- Signal too low - intermittent
2. 17952 - Angle Sensor 1 for throttle actuator (G187) P1544 - 35-10 - Signal too large - Intermittent
3. 17580 - Angle Sensor 2 for throttle actuator (G188) P1172 - 35-10 - Signal too low - Intermittent
4. 17961 - Barometric / Manifold pressure Signals P1553 - 35-10 - Implausible Correlation - Intermittent
5. 17912 - Intake Air System P1504 - 35-10 - Leak detected -Intermittent

I fear the last fault (the leak) the most, coz leaks are usually hard to find coz it can be anywhere n i may or may not be able to find it. darn!!!

just got my 30miles done, so leaving for test now...shall update in couple of hours

btw where is your garage? sounds quite fair practice..

 

[audio]

Alright, the fault no 1,2,3 and 5 have gone now and the one 4 remains. So i guess its the intake manifold pressure sender/thrust sensor then. the car stalled in the garage and all the lights lit up along with the engine management and the diagnostics showed somthing to do with ECU which i didn't really care about coz all the lights except the engine management light went off on turning the ignition off and restarting the engine and I really HOPE that was glimpse of its old cruel memories which i dont wanna PAY more for...lol. hate paying for vagcom/diagnostics job...darn it hurts! leicester audi says 41+VAT for sensor, will do next week. will update...till then tata!

 

[murran]

was going to say that, id delete all those and take it for a drive.

id pull the sensor out and clean it. it gets the same sort of gunk on it that was on the throttle body.
sensor is on the left hand side bolted into the end of the inlet manifold, has a 4 pin plug onto it. its held in with 2x t20 torx screws. its a little fiddly to get out with the wiring loom and the dipstick tube in the way. give it the same carb cleaner routine as the throttle body.

did the garage rest the throttle body adaptions??? if they didnt it might be the cause of the map sensor fault. as throttle position has a direct effect on what the pressure (vaccuum) in the inlet manifold.
what are the actual values coming from the "map" sensor (inlet pressure sensor) should be around 260-280 on tick over. up to near atmospheric 900-940 under full load and down to 180-250 under engine braking.
it flags up this fault when the map sensor reading doesnt make sence compared to what the ecu should be seeing under certain driving conditions.

 

[murran]

double posted

 

[audio]

replaced the sensor and the car drove much better than before but now acting annoyingly bad. all the lights in the dashboard turn on especially while driving slow. EPC, traction, EML, ABS and three beeps along with flashing brake signal in the info lcd. the engine loses power badly and the car hardly drives max till 40m/h. intially it would all go off once i restarted but now it happens soon after coasting. doing 290 miles for a tank of v-power. any advice???

 

[murran]

brake light switch? do the brake lights stay on with your foot off the pedal when it does it?
other than that, i dunno, there could be a problem with the load signal from the engine to the brake ecu.

from all the trouble your having. buy one of these. for what you paid having your fault codes read at the garage you could have bought one of these and check/reset your own fault codes when ever you like!
Autel VAG 405 Diagnostic Tool for VAG group cars | eBay
Vag405 Car Diagnostics Machine | eBay
i have one for doing fiddle jobs out of work, i cant rate it highly enough!

 

[audio]

many thanks, i have ordered the vag device and shd be here by thursday hopefully. i have been told about the brake switch going wrong by a few friends too but the brake lights dont stay on by themselves as far as i know. Somebody also blamed the weak battery, do u also think so? does this vag device also reset adaptations?

 

[murran]

how do you mean weak battery? if the alternator is charging and the car starts fine then id say not.

never actually used it to reset adaptions. hmmmm. i dont think it does.
you need to spend like 200 on one to get all the diagnostic side of live data and adaptions.
think its this one for european stuff.
AUTEL MAXIDIAG EU702 CODE SCANNER DIAGNOSE BENZ AUDI VW OPEL VOLVOOBD2 OBDII | eBay
Autel EU702 Airbag ABS Engine MIL Light Reset Tool 030 | eBay

 

[murran]

vagcom is good but dragging a laptop around is annoying and you cant really leave it in the car. these little code readers fit nicly in the glove box. takes literally 10 seconds to plug it in, check an ecu, write it down and delete it.

 

[audio]

thanks for your support i think i'll stick with vag 405 for fault reading. detailed/live data stuff is rarely done for which i can rely on vagcom buddies. i think i should be receiving the device tmorw. i'll keep u posted

cheers!

 

[audio]

Got 2 issues here:-
1- 17961 Barometric Manifold pressure signals: implausible correlation.
2- 01314 Engine control module-sporadic 013, check DTC memory.

checking the readiness:

EVAP, catalyst, o2 sensor and EGR sys FAILED.

your comments plz.

 

[murran]

map sensor fault. implusible correlation. did you have the adaptions reset after youd cleaned the throttle body?
and an engine ecu communication fault. (this is probably why the abs/traction lights are coming up too). unsure of the fix on this tbh. still might be load signal to abs/traction related coming back to the map sensor tho.

wierd.

reguarding the readiness thing, i think if theres a code stored relating to the control and functionality of the systems you mentioned such as evap egr etc. then they are disabled to a limp home mode probably why they are listed as failed. they should be "ready" not "failed".

the map sensor is an important sensor.