Hard start & rough idle when cold

[Bill Green]

P.S. I just double checked the temp sensor and thermal time switch as well.
The gauge on the dash has been reading way too low for quite a while now. It
reads off of the thermal time switch (according to the electrical schematic)
so maybe that is also what the ECU uses? That would add up to being the
problem if that's the case. At any rate it needs to be changed obviously so
I'll change it and we'll see.

Thanks!

-----Original Message-----
From: Huw Powell [mailto:audi at humanspeakers.com] 
Sent: Tuesday, February 09, 2010 8:28 PM
To: Bill Green
Cc: 'audifans'
Subject: Re: Hard start & rough idle when cold

Cool, thanks.

OK, this is weird.  When *cold* your car is running in closed loop 
(therefore no enrichment and crappy running) and when it warms up it's 
going to open loop (ECU ignores OXS and runs engine a bit rich, hence 
the high idle I think you mentioned), seems to me.

Are you *sure* that engine temp sender is working properly?  And is the 
correct part?

PS, I'm adding 4kq back in here so people know what system we're talking 
about.

Bill Green wrote:
> I just went and checked it again. I inserted my multimeter in the single
> line from the sensor to the ECU. When the engine was first started it
> fluctuated between .2 and 1.0 for thirty seconds or so. Then it settles
down
> to fluctuating between .53 and .55, After fully warming up it drops to .52
> to .53, If I rev it as you suggest it momentarily drops to 4.9, Actually
> replacing the sensor improved overall performance but not the starting
> problem. 
> 
> 
> "The O2 sensor is new and reads .5v with very little fluctuation."
> 
> Then it's not reading (sorry not get to this earlier, thought of it 
> while grocery shopping).  The wire from the ECU itself will read 0.5 
> volts.  On a non-managed engine, the OXS will almost certainly read 
> almost zero or almost one volt.  Are you sure it's plugged in properly? 
>   Did this problem, um, start when you replaced it?
> 
> Try reading its output while revving the engine up and down a few times...
> 

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/