schnitzelboy

I had a few stumbling problems and got the following codes: 17912, 16845, 16556, 16559. I replaced all of the vacuum hoses, including the throttle body to plenum hose and, of course, the damned valve cover hoses which broke when I pulled the plenum. I also replaced the fuel filter since I knew it could contribute to stumbling problems, and I cleaned the ICV. Then I cleared the codes.

Now, when I start the engine I get a knocking sound when the engine is cold. The sound increases in speed when I rev the engine, but it goes away after about a minute.

When I blip the throttle it takes a while to come back down to idle and has a stumble between 2K and 1K while it drops down.

When the engine is cold, the idle stays steady at around 1200 RPM. When the engine reaches operating temp, the idle drops down to about 800 RPM (very suddenly) and the CEL comes on immediately, throwing a code that wasn't there before:

17514 - Oxygen (Lambda) Sensor: B2 S1: Voltage too Low / Air Leak

I assume this is an air leak, but where? Could I have done something wrong in re-attaching the intake plenum? The knock kind of worries me.

One more thing--I was working on the car in a windstorm and when I moved it, there was a mystery object underneath. It's a hard rubber spacer about an inch long with a diameter a little bigger than a Bic pen. There's a flange on top--it looks like a well-nut but with no nut at the bottom. I'd post a picture but my digital camera isn't working. Does this sound like something related to either fuel filter, intake plenum or ICV?

Thanks in Advance.

Steve
'96 A4 Quattro

Digit@lex

As for the O2 sensor, is it the original?

schnitzelboy

It is the original 02 sensor. VAG-COM says it's either the sensor or a vacuum leak. I'm assuming that since I've been messing around with hoses that it's vacuum related, but I could be wrong. I'll check the 12V forum for the mystery object.

Thanks,

Steve
'96 A4 12V Quattro

schnitzelboy

Both mysteries solved. The mystery object is the bushing that goes between the plenum mounting hole and the throttle body mounting pin. Now I'm wondering what happened to the other one, and whether it was perhaps ingested by the engine. I hope not.