Idle/Stalling Prob

[Niggy]

I'm having a problem with my 97 1.6 A3 (one of many problems i've had /ubbthreads/images/graemlins/cry.gif).

When idling, the revs fluctuate. It generally idles at about 1k but sometimes drops to about 500rpm and occasionally races at around 1500 rpm - this is at its worst when lifting my foot entirely from the throttle or in the first portion of its downward travel when you can see the revs "drop off" or blip under normal idle leading to a stall though sometimes the ecu?? seems to catch it in time, preventing the stall.

This sometimes has happened whilst moving when I have removed my foot from the throttle, which is obviously dangerous as you lose PAS but generally occurs at lights when accelerating and lifting clutch at same time. (I have to overrev before lifting clutch now to get over initial blip - which sounds terrible)

Having looked at few similar posts to this I intend to check...
Throttle body (clean)
ECU (unplug or disconnect battery)
Coolant temp sensor (no idea about this)

The coolant temp sensor seems like a favourite as the problem started about the same time as I got a hole in my radiator and I tried using radweld (or similar) and I wonder if this has fouled the coolant temp sensor.

If anyone has any other ideas or advice on doing any of the above I would be grateful.

 

[Khufu]

The coolant temp sensor's condition can be ascertained if you can meet up with anybody with VAGcom. I suppose you could also check for any leaks in any of the air hoses/vacuum pipes or intake system. This can weaken the mixture and the ECU will try to rev to compensate. I guess you could also check the throttle position sensor. It should be connected to a 8 pin connector on the throttle housing.

The resistance between pins 4 & 7 sould be 1000 ohms.
With throttle close pins 5 & 7 1500-1600 ohms and fully open, 700-900 ohms. For the idle speed actuator, 1 & 2 3-200 ohms and for the actuator position sensor 4 & 7 1000 ohms (as above) and 7 & 8 1200 ohms

Hope you get it sorted, and welcome to the forum.

 

[AndyMac]

Get the water pump changed pronto, sounds suspiciously like it's starting to seize up, thus loading the idle speed and making it irratic, especially after using radweld. If it seizes completely it will strip the timing belt (not good). I had this on my A4, but luckly it was leaking slightly so we swapped it out and problem solved. The old pump was so manked up that you could hardly turn it by hand.
The radweld maybe disguising the fact that it's leaking. Water pumps tend to let go around 80-100k miles.

 

[HTC]

I'd personally go for the coolant sensor too.

 

[Gambba]

[ QUOTE ]
Mad Matt said:
Hello There,

I've also experianced the same problem, which replacing the Coolent Temp Sensor did not resolve the issue at all. From what many people have advised on this forum it seems no one can def give the answer to the actual fault. People whom have taken their cars in to Audi just get their I.C.E blamed for it, saying it's drawing too much power. Cough! Cough! What crap when u even disconnect ya sub etc, the fault still occurs. Anyway.....from what Rob has put i might just try a New Battery and i'll let ya know how i get on then that might be 2 successful fixes.

Thanks

[/ QUOTE ]

Well nobody can give an actual definate answer on a specific problem due to the numerous components that enable the engine to run. Coolant sensor is a favourite without a doubt but it's not a certainty as with any suggestion especially regarding stalling and idling issues unless you can hook up VAG-COM and check specifics, which aslo aint that easy.

First of all go around the engine bay and wiggle every wire you can see and disconnect and reconnect every plug you can see. Check the black box on top of the battery for corrosion and losed connections, as I've heard of this causing issues. Dissconect the battery for a few minutes and then reconnect. Next disconnect the MAF (This will log a fault code, but probably not bring on the engine warning light) and run the car, if the problems gone and all you now lack is power then you've most likely found your cause. Whip you spark plugs out and check them, give them a clean up and pop em back in. It can also be worth running some injector treatment through the fuel system, as it's relatively cheap and can't do any harm and will hopefully remove any carbon deposits on the injector nozzles and possibly any small crap in the fuel lines.

The above is a brief guide and avoids replacing components and should be acrried out one at a time with a test drive in between.

 

[AndyMac]

When disconnecting the battery you have to leave it disconnected for about an hour so complete a full ECU reset.

 

[AndyMac]

Also try using Optimax for a few tankfuls. I found this gives a much smoother power delivery and better fuel consumption. However, seems to now rebel a bit if I use anything else, I think they use the same drug in Optimax that they use in Whiskas cat food.

 

[Niggy]

Thanks again for all of your help and welcomes (though I did knock 'round here in the old days of audi-sport, before it (ahem) reorganised and I lost my post count - nice to see that everyones still as friendly and helpful as ever)

Last night, I cleaned the throttle body and pipe between this and airbox - whilst doing this I noticed that the small section of pipe connecting main pipe to just below oil filler cap was very mishaped and had a small tear in it. I have applied some tape temporarily but will obviosly need to replace this pipe (escuse my ignorance but what is it called - induction pipe? air filter pipe? vacuum pipe? & how likely am I to find one of these locally - would most motor spares shops stock them?)

I also disconnected battery for an hour-ish and added some injector cleaner to fuel.

Anyway, it seems as if we have gotten somewhere /ubbthreads/images/graemlins/wink.gif, on run to work this morning the idle certainly seemed more stable but was maybe a lttle high (about 1200-1300).

Intended to clean MAF last night but ran out of light, so will have a go at that tonite (heard that IPA is good for this but also read that I can use injector/carb spray- is this OK?), hopefully whilst replacing that pipe.

Then its a matter of getting my hands on Vag-com and reseting my throttle to the ECU and checking coolant temp sensor.

Think I'm gonna start using optimax as well, sounds like its worth the extra!

Thanks again /ubbthreads/images/graemlins/beerchug.gif

 

[LeeW]

I've got a lowly 1.6 too and the idle is as mentioned here only not as bad. Also the accelerator pedal has a mind of it's own and I can feel it jerking under my foot at times. It's been serviced so plugs etc have all been changed and have been using optimax for a month or so. Think I'll try what's been mentioned here and see how it goes. It does seem to run better with optimax though.

 

[neversaydie]

Had the same problem Brought it into VAG and they fixed it - I know the coolant temp switch was replaced and they also cleaned the throtle body. No problems now.

I also now use and only use RON 97 petrol. Been great since.