Hard start & rough idle when cold

[Bill Green]

The temp sensor was bought a few months ago, it is an aftermarket brand .
The ohms for a given temp checked out correctly. I guess it could be the
wrong one but it does appear identical to the Bosch one I took out. I
replaced it thinking that could be the problem. I'll see if I saved the
Bosch one and put it back in tomorrow. 

Thanks for all your help!


-----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/