audi 100 engine hunting

[gags100]

On Sunday whilst stuck in traffic the engine started to hunt (going from 900 to 2000 R.P.M.) I have cleaned the idle stabilizer out and ran it with temp sender disconnected, as this has been working intermittently since i had the car, don't think that to be the problem. This is the normally brilliant 2.3 5 cyl. Now 2 days later when cold, ticks over at 2000 rpm then starts hunting when warm.hopefully someone on the forum has cured a similar problem /ubbthreads/images/graemlins/thumbsdown.gif
please help

 

[madvw]

sounds like the ISV may have completely packed up.

 

[scotty33]

I've had issues with ISV's, tend to stick at
1500 rpm when the weather is cold. Can usually cure this with a clean.
I read that the temp sender has an input
into the ISV function on the 2.3. Might be partly to blame.
Also a duff lambda probe can cause the idle to go nuts, because the mixture goes rich... which you would notice as poor mpg. You can test the lambda with a meter, leave it connected up, but stick one meter probe to the black wire, the other meter probe goes to a good earth. Set to Volts, with car running and warmed up you should see 0.2v approx rises to 0.9v approx, falls back to 0.2etc. should oscillate once per sec. If the sensor is dead it will read constant at (I think 0.9v)
Could also be Vac leak?

 

[audi5e]

The ISV's on these go bad after a while and do need to be replaced (cleaning only works so many times). Also get a new temp sender as that sends signals to the ECU (as does the lambda, the knock sensor, engine speed sensor, hall sensor, some models have others sensors in addition).
If the signals to the ECU are incorrect then it will send the wrong control signals to the ignition and to the fuel pressure regulator on the fuel distributor. Also if you have an automatic gearbox, that too will get bad info. Also make sure that the thermostat is in good condition as the ECU will adjust according to engine temperature.

You might want to clean up all the wiring plugs on the car while you are about it.

Your problem of hunting is described on many web sites and is going to be the ISV for sure.

Vacuum leaks would cause other symptoms such as poor starting, stalling, rough idle

 

[gags100]

Cheers Guys. I am keeping my eyes open for an I.S.V. and possibly a temp sender unit, I will let you know what the results are. had no trouble today but i'm not travelling to far to work.Have been offered an I.S.V. FOR £30 is this reasonable, it is used by the way. thanks again

 

[madvw]

if it works, £30 is fine. If your going to keep the car for ages, may as well buy a new one for about £85 quid (well, was the last time i looked).

 

[deemde]

Check for water in the passenger footwell! I had bad leaks in the bulkhead to inner wing joint (caulking had deterioated). Water got into ECU wiring. Quite a common probelm, I believe, with 100/A6 models. Causes lots of other engine management problems, including hunting!

 

[gags100]

After going to the dealership i have cleaned out out the I.S.V. again. The price for a new one is £225. Luckily this seems to have cured this problem. I think the dealers should keep smelling salts handy to help bring you round.I will be keeping my eyes peeled for a scapper though. many thanks for your replies