Ok, it mainly pertains to the Motorgeek thread below. In the past when a car would run crappy when just started I would (maybe I was told by somebody) disgregard the O2 as the culprit, since the car is cold and ECU hasnt started to look at the O2 reading yet. But judging by what Natrix said, the O2 could be the problem, so it has my confused.

Can some experts shed some light on this for me?<ul><li><a href="http://www.motorgeek.com/phpBB2/viewtopic.php?t=25075">http://www.motorgeek.com/phpBB2/viewtopic.php?t=25075</a</li></ul>

The old ones used to rely on exhaust gasses to heat them up. Newer ones have a heating element to help them reach operating temperatures sooner. I'm not familiar with how soon the ECU looks at the data but if it is looked at right away in a newer car that shouldn't matter. Wait for it to get warmed up and then test as usual. Probably best not to rule it out until it is checked properly.

In my posts I was ONLY referring to the older Audi engines, nothing new at all (the car in question was a 4kq).

If Nate is correct then whenever somebody posts a bad running car at startup or when cold, we should be looking at the O2 as a culprit. That doesnt make sense to me.

Before the car has run, turn the key over to just before ignition (so all your lights and fuel pump come on). Let it sit for 15-30 seconds. Reach under the car and feel around the o2 (the bung its in, the exhaust tubing, and maybe the o2 itself but could be blazing hot by then...). Obviously if it's warm/hot it's self heating.

Poor running when cold would point me more so towards vac leaks, cold start valve, and A:F ratio...

I had to convert my car to a 3 wire when I used the 5-3-1 4000q exhaust manifold and downpipe.

But in the caSE of JT, ecu doens't look at o2 until warm.

(As I know, when I had a really bad o2 sensor)
Would work fine for a bit, then when warmed up, would die. DIsconnecting the o2 sensor fixed problem.

Sensor had died when I went through a big puddle, and was putting out ~3v, totally confusing the ECU. O2 sensors never put out more then 1V, so it must have crossed over to the heater power somehow.)

As undoing his o2 sensor didn't do anything, I'm betting on that guy having the 'bad temp sensor' problem.. :-)

That was the first thing I asked, along with the ground on the intake manifold. He says that sensor is fine, so who knows.

Only reason I posted this was due to the O2 information Natrix posted. Didnt make sense to me that the O2 was the guys problem if it persisted when the motor was cold.

sensor = fine means what?

Depends what he did to test it.

From what we know from posts, the 'base mixture' is 'sort of' ok, as it runs with the dpr wiring undone (actually, it should run a bit lean then). so something is still up..

Only way DPR makes mixture rich is from temp sensor, 02 sensor, or altitude sensor.

So pick one of them as a troublemaker... :-)

I told him to look at the intake manifold ground and that coolant temp sensor. He said "it was fine", so I almost would feel like an azz if I said "well, did you properly test it?"

Thanks for chiming into that thread though, your insight is always awesome to see when it comes to this stuff.

&gt;your insight is always awesome

Insight? Ha! IT's more 'experience of the hard knocks' = BTDT

Thinking about it, I've had my 'winter' 4kq for just over 10 years now..

Seen a lot of things go wrong, so figured out a lot of fixes!

Had all the classic 'spare fuse' and 'bad ecu ground', 'intake leaks' and broken door handle problems.. :-)

I have a el cheap o O2 meter plugged into the sensor..to at least tell me if things are sorta OK... but recently theres been a loose connex ..so Ive learned some about the o2 function.. On mine which I think is a 3 wire one too, the el cheapo gauge doesnt read anything for about 5-8 min or so of running when the car is truly cold.

The other interesting thing I found out due to the loose connex, was that when the circuit was open and not providing any sensing.. the car ran fine at fullish throttle...but it hesistated at anything less.. I really dont know why, except that I gather the ECU assumes a mid-value when theres no O2 input, and maybe since I have the AF ratio fairly rich, it needs the O2 value different..?

Anyway thats the sum of Hals knowledge on o2 sensors.

That's up through the 05's I've worked on, anyhow. Haven't had to dig that deep on anything newer yet ;-)

Tony