Air/fuel/sensor Issue. Where Is It?

[Guest ziphus]

Hmm, got my GTI (87 1.9 8v GTI) a couple of weeks back. She's a bit rough, but is a project car and and slowly making steps in the right direction. I'm currently down to the following situation.

 

The car runs well when totally up to temp (although this take a long time because i think the previous owner has removed the thermostat. i'm replacing it tomorrow). At normal running temp, it runs smooth (after a couple of service components, timing adjustment and new timing advance unit), decent power for an old engine, idles quitely and stable.

 

However, stop the car, let it totally cool down. Ie, start the next morning and it starts first time, but will not idle at all. Turn the mixture/idle screw 2-3 turns out and it will just hold an idle, extremely low and not very stable. In this state it will also blow a bunch of light black smoke. You drive her around like this for 15 minutes and the idle and smoothness slowly build up with the engine temp. By the time it's up to temp, the idle will be smooth, but up to around 1.5-1.8k rpm. You can then turn the mixture screw all the way in and it will go back to perfect idle around 1k. At temp the smoke is basically gone.

 

I think there's something up with air/fuel. Obviously there are many places that this could be affected, including components in the intake tract and sensors feeding the cpu with data.

 

Any thoughts on what's going on here? Anyone had similar experiences?

 

Any help is appreciated. It may save me a length process of elimination!

 

-Jordan

[Mikey G 3]

Sounds like the Supplementary Air Device (SAD) which controls the cold idle speed.

Do a search as it is a very common problem.

 

Also which screw are you adjusting? as the mixture and idle screw are seperate screws, mixture on the AFM and idle in the throttle housing.

[Guest ziphus]

Sounds like the Supplementary Air Device (SAD) which controls the cold idle speed.

Do a search as it is a very common problem.

 

Also which screw are you adjusting? as the mixture and idle screw are seperate screws, mixture on the AFM and idle in the throttle housing.

 

That was another thought that I'd had, but when I speak to local french parts places the look at me crossed eye like I'm talking about a russian car or something. Apart from Supplementary Air Device (SAD), what else are these things referred to as?

 

I'm twisting the one on the throttle body.

 

Thanks again.

[Guest ziphus]

Ahh, cold start valve. Gotcha. I've got something valve looking in that regrion, however it seems a little different. Will report back.

[Mikey G 3]

The SAD is sat just below the thermostat housing just above the gearbox. There is an air pipe coming off the rubber bellows between the AFM and throttle body, this then goes into the SAD (cold start valve) and back down to a fitting underneath the inlet manifold just behind the radiator and in the middle of the plenum chamber.

 

Hope this helps

[Guest ziphus]

Just thought I'd post a reply for anyone else that comes across similar wierdness.

 

I had changed my plugs as a matter of course after buying the car without taking too much notice of their condition. But Just a day after writing my last post, they fouled again. After only 1.5 weeks. This time I checked their condition thoroughly. They were caked with carbon deposits. Over fueling!!!!!!

 

So anyways, I had already double checked a lot of components related to fueling and various ECU inputs. The last thing was the oxygen sensor. I couldn't be bothered messing about with tests knowing they the should be replaced every few years anyways, so I got an after market sensor for a 405 and put it in. Presto, she's a brand new car. Starts, idles and runs reasonably when cold and runs like new from just above dead cost upwards.

 

The best thing is that the smoke I was seeing has disappeared and she's using far less fuel. I'm glad I persisted with auxiliary bits before looking at engine internals.

 

Just goes to show, do your home work and be persistent. It could save you big $$

 

-Jordan

[Mikey G 3]

So you have an 87 car with an oxygen sensor?? They must have been introduced earlier down under then?