Hello,
I was having very infrequent difficult starts, finally figured out the pattern that it happens when the car is warm.
Typical warm start scenario:
Drive 10-40 miles, buy gas, very hesitant restart.
Quick 5 minute stop at a shop, same thing (so it is not related to gas)
Today it just would not start until 4th try with some wait time in between, it is clearly degrading.
Never first thing in the morning or after work.

I will appreciate any ideas.

If there is a bit of an incline (forward down) that also may be a factor or sperate problem but most recent ones the car was completely flat.

Thanks!

 

Search "coolant sensor"

 

I would agree based on what I have read while researching the same problem with my '01 A4 1.8T, here is a link that might help with DIY. I plan on doing mine when it finally gets warm enough up here in MN to work on it. Hopefully the car doesn't make the choice for me.
http://www.audiworld.com/tech/eng47.shtml

 

If it happens after filling with gas, it is most likely the EVAP system valve that is located right behind the airbox, It will be about 1.5 inches in size and have electrical connections and hoses coming out of it. The part is about 50 dollars and a 10 minute DIY replacement.

Otherwise, it is likely the temperature sensor. Also an easy DIY and a cheap part.

 

Thanks so much for the notes!
Audi service took a aquick no charge look--no charge because they owe me from past blunders.

They tend to just look at the codes and propose to replace any part related to the codes. This is what they came up with:
Need to replace throttle body 878$
Coolant bottle has a small leak 234$ (I have seem some leakage under bottle they are right, it was not low on coolant though)
Thermostat may need change they could not confirm. 575$

I did nto authorize any of these. On thwe way back I saw temprature go up to maybe 200 or so on a 5 mile drive, the sensor is not completely dead for sure.

Someone may have bumped a clloant hose while changing filter.

What would you recommend on the throttle body?
Change thermostat and see if problem persists, based on the advice of david9999?
I have a dcom cable on order, should be here soon, if the engine check light comes back.

 

thermostat and coolant reservoir cn be DIY easily. throttle body is not a very likely cause. and wut is a dcom cable? do you men vagcom? thermostats is like 30-40 bux at autozone.

 

They WANT to replace the throttle body -- they don't need to.

If they insist it's giving you trouble, go ahead and see if you can clean it out, either by yourself or have them do it. Replacing it is retarded.

 

well, I mentioned that I hope the car doesn't make the choice of when I do it for me and it has. My wife called last night stranded on the side of the rode. Stopped by the dealership and picked up a coolant temp sensor and an Engine Speed Sensor. I decided to start with replacing the Engine Speed Sensor because it was easier to get to and it seemed to do the trick.

Also, I had one other symptom that you didn't mention, have you had your EPC light come on at all? After about 15-20 minutes of driving the car would momentarily lose power (RPMs drop to zero and then bounce right back up) followed by the EPC coming on. The speed sensor seem to fix all of this for me.

 

Yes, I have the same. I had that for a long time, similar trouble rootcausing it, seemed to reduce a lot with an accelarator pedal replacement which was persistently showing in codes.

Now my EPC light still comes on occasionally. It is tied to mechanical vibration, it may be the lane dividers at 50Mph is enough vibration to kick that on.
What you describe makes a lot of sense that it would be the speed sensor for you.

I got an engine temprature sensor from Rock Auto, the only one day had for a 2000 Audi 1.8T (B5).


I looked at replcaing in the sensor in the above picture. I hestiated and left it in because of two reasons:
1. Mine does not have the blue connector with a metal clip I saw on other pictures. It is a black sensor, part number mostly matched what I read at http://www.audiworld.com/tech/eng47.shtml
but ended in C and has a plastic retainer clip. I could not get the cables out of the sensor without tools as I expected. Am I supposed to use a screw driver to lift the tab in one of the faces? Did I just have to pull harder?
2. I also ordered the 7$ flange in case it comes up tied to my minor coolant link or overall problems. The flange has 2 sensor holes, my flange under the blue circle above has only one sensor slot. This is the second reason, I lost faith in Rock Auto parts sending the right parts. The sensor they sent is an after market green AIRTEX Part # 5S1478, looks right, but I am hestitant having seen the flange not quite being right.

I dont think I need the flange job now , the leak is directly under the coolant tank in picture above and is minor. I got a replacement tank as well. I wont touch that yet until I get a better look in there with mirrors, it came without rings and I suspect my problem is one of the connections ... and not the tank as dealer claimed--to justify 575$ for their work.

There are 3 sensors under the coolant tank mounted on the firewall. Middle one has a blue connector like what I was expecting for the engine coolant sensor, and a green one on the right. What are these two? Here is a picture which may help:


My wagcom cable arrived (sorry not dcom) but has a serial port and is thus not useful for me. They have been resending a usb one for a few weeks now.
Thanks for any advice or confirmation that I am replacing the right part.

 

Getting the pictures right, first one shows location of sensor I am replacing in the grand scheme of things.
http://farm4.static.flickr.com/3096/...f4951e.jpg?v=0

I am curious what these blue and green sensors are under coolant tank in the back:
http://farm4.static.flickr.com/3067/...431d8f.jpg?v=0