Revs hit the floor!

[GazzaG60]

unplug the isv and try again. it may not start that easy but when it is it may find your issue for you.

seen plenty of this type 0of issue with idle valves. idle goes rock steady when unplugged. only issue in audi is no throttle screw to adjust. you need sometimes to wind the butterfly out a tad.

pugs also have these idle valves. one of the only bits not rusted away after 10-15 years on one of them.

[Henkjan]

my guess would be the throttle 'potmeter' (is this the proper english word? it's the thing on the throttle that gives the throttle position to the ECU) that will not give the richt signal to the ECU, and without the ECU controlling the ISV it does nothing..

I have the same problem.. test this: does the fuel consumption on the BC go to 0.0 l/100km before it dies? the fuel shut-off uses the same signal.... I have the same on my S2, and I noticed that if the BC reads 0.0 then idling is OK, if it is not it will stall (or drop to very low revs). no blink codes, but on a Bosch computer it reported a fault in the potmeter. I have not yet found the time to replace it so I cannot positively report that this fixed it...

[Fat Audi 80]

I would agree with both the above posts, but suspect the ISV still. Do as gazza says and it will tell you if the ISV is shot or not. (I did not think VAGcom could tell if the ISV was fully working?)

After that try the Throttle potentiometer (Close Henkjan)

Cheers,

Steve

[Paulgo]

Thanks guys - I will have a go at unplugging the ISV and logic would say it has to be something between that and the TPS as Henkjan and Gazza suggest. Does it matter if I unplug the ISV after the car has warmed up btw?

[terrybullwon]

I had the same problem like Ross said. You can test the ISV with 12v. Also check how clean your throttle body as you should see light through it when you hold it up and look.

[veneto rs2]

Hi
I had the same problem for ages....and i mena years!
Idle was perfect in winter or cold weather and start to do that annoyng problem on trafficlight/cornering/stopping slowdowns in summer time...
I cleaned the ISV with buckets of WD40 several times changed the MAF cleaned the air filter.. but in hot weather (A/C and radiator fan on) it camed back again.

Eventually i found that the 90° bend pipe that goes from the ISV to the gasket had a crack on the inside part very hard to see it.
I could see the crack just with the part in my hand while forcing it to open the 90° bend.
Never had the problem again since the change.
The crack was'nt a issue when there was no services like A/C and radiator fan operating.
On hot weather with services on an amount of air was sucked or blowed (i don't know which..) from the ISV trough the crack that made the strange behaviour.
I think that pipe and all of the small ones around throttle body worth a check when bad idle issue come out.
Hope this helps.

Stefano

[Fat Audi 80]

/\ /\ /\ /\ Good tip that thanks!

[Jas11n]

Output test in vagcom ran on the ISV, clacking away like a good un.
TPS switch was fine too.

[Fat Audi 80]

Fair enough.

[Paulgo]

Cheers guys

As Stefano suggests it sounds like I need to examine the area around the ISV more closely – I have removed it a couple of times recently, either to clean or for access and it is possible that something’s has got damaged / spilt etc. As Jas says it was clicking away under vag-com but there could well be something that’s not specifically the ISV but part of the system thats t the culprit and only shows under certain conditions, as Stefano found. It never shows any symptoms when cold – only when the engine is warm. Don’t have aircon and its not happened yet when the car has been hot enough for the fan to come on.

Will also check around the throttle body – I recently changed the leads and it is a bit tight where they pass under the area where the TPS connector is. Always a chance I might have caught something around there also

thanks again

Paul

[Markarina]

Sounds very similar to the problem that Paul had - see here