Hey there new to site. I have a 1999 2.8 quattro with no check engine lights or codes set but car is rough idling and hard to start only when it's warm. Cleaned maf not sure where else to look. Any help would be awsome

 

Could be the coolant temp sensor. Cheap and easy replacement. Be sure to get a new clip that holds it in as I almost always break the stupid things getting them out. Here's one on ebay for reference.

Audi VW Bilstein Coolant Temperature Sensor Water Temp Switch 059 919 501 | eBay

 

I will try that. It's wierd that it's only when vehicle is warmed up. Does the audi have a serperate sensor for the temp gauge then? Could temp sensor affect mileage? I'm averaging 20 now and 90% of my driving is highway

 

The temp sensor has 2 circuits in it. One for the ECU the other for the dash gauge. If the ECU side is not working correctly, it can report the wrong coolant temp to it and cause hard starting problems and, possibly, make it do wonky things with the fuel/air mix that may affect mileage. The one in my 03 A8 went nuts last year. The gauge side never really worked since we got the car but it started to get hard to start. I connected my OBD machine one day and watched the data as I was driving it. I happened to be looking right at the coolant temp when it went from 190-something down to 70 for about 5 seconds. That's when I decided to research the temp sensor. I went ahead and got one for good measure. Took 15 minutes to swap out. Gauge started working properly and haven't had a hiccup since.

 

did live data on temp sensor didnt show signs of a problem. i still changed it and made no difference. car still hard to start when its warm. also worth noting is that the car seems to start right up if i turn it off and then start again immediatly. but if i get gas or let it sit for like 30 min its very hard to sart. to get it to start i have to give is half throttle then it starts. it will also stumble very hard for a few seconds and smooth out... most of the time

 

I'd see if you could get a reading on the fuel pressure. My A8 was also doing that sort of thing not too long after I got it. Turned to be the fuel pump. However, try this test first. Disconnect the MAF sensor. The ECU will run the engine without it. You will get a code for it but the engine will use the other sensors to make it run properly. If the MAF is bad, it can be sending bad airflow data to the engine causing it to do wonky things like that. If it doesn't fix it, at least you've eliminated the MAF sensor. Back to a possible fuel delivery issue.