pretty much since i have owned my audi 80Q i have been plauged with rough starting from time to time. Some times it cranks over hard or takes two trys to start, or it starts fine and then i go and put it in gear and try to drive its like it has no power (goes away after a few seconds and drives fine). It only happens on cold starts. Also while driving some times when i push in the clutch the idle will drop under 1k, some times down to 500. I was thinking maybe the 02 sensor was bad, but wanted to know if maybe anyone had a similar problem, or knew what could be the cause.

I gave it a tune up including the following to try and fix the problem
Spark plugs
SP Wires
Distributer
Rotor
air filter
fuel filter
fuel pump (was really noisy so i thought it might have been the problem)

 

Seems like a common problem with the CIS-E cars, my 1991 1CQ does exactly the same thing. I am still in the process of finding the problem to this one. It is a real PITA especially if you have to pull up hill with the engine cold. The strange thing is that it only happens once after a cold start it is as if the engine management needs to get some sort of a reference

 

Its deffinitly a real PITA, if you find out anything let me know. Also what have you tried to replace in fixing the problem?

 

I did a bit of a research this morning and it is definitely a common problem especially with the Quattro models. However these posts go unanswered, there are a few suggestions but nothing that I haven't tried. I suspect that it is more noticeable with the Quattros since more power is needed for the added weight as well as the AWD system itself. I plan on hooking up a couple of gauges to see what the fuel delivery is doing during this time. Temperature doesn't seem to matter, whether it is -15 or +95 it still bogs down during that first initial throttle/load after sitting a few hours. I also noticed that if I drive slowly on a level road (5-15mph) the car would bog down once I crack that throttle open. Even if I let the engine warm up for a few minutes that initial open throttle is a problem. After that it runs OK.

So far I have:
Replaced the Hall element in the distributor.
Balanced the injectors as well test them for spray pattern and volume.
Tried using different ECU's (Timing and CIS).
Checked Mass Airflow for binding.
Cleaned the ISV.
Checked all the throttle miscroswitches.
New injector shrouds and O-rings.
New Fuel filter.
Resurfaced head.
New valve seals.
Cleaned and lapped valves.
Installed K&N filter.
Installed Sport cam.

 

Thanks for the info, Well im still going to replace the O2 sensor as im pretty sure its bad and my cat is toast anyways so i mind as well change them at the same time. Keep me posted though if you find a good fix. I will let you know if the 02 sensor helps at all, but im not really counting on it. On that note does anyone know where i can find an o2 sensor for under 100 dollars?

Thanks

 

...I also noticed that if I drive slowly on a level road (5-15mph) the car would bog down once I crack that throttle open....

I double checked it today and it is less than 10mph!

You can find an O2 sensor for about $80 maybe even less at places where you pay for shipping. The problem is that they are universal types and require splicing. Where as the OEM have the all the necessary connectors. I think that a new sensor isn't going to do much. The sensor only helps to fine tune the emissions through differential pressure regulator. Most people that I spoke told me they haven't noticed any difference but do keep us informed.

maximumautoparts has one for $82 plus free shipping

 

Universal, or OE?

 

Checkout oxygensensors.com they have a universal for $44 and a Bosch universal for $90. Personally I would only go with either Bosch or Denso. I believe Denso is licensed by Bosch to make them for the Japanese makers.