2003 Audi A4 1.8T Quattro
133k Tip-Tronic

Hey guys, i am having an issue with my Temperature Gauge and now the way it drives. Let me give you a breakdown of the issue.


1. Had a leak in the Thermostat Housing of my Car, Had it Replaced. Car Runs Fine

2. Noticed that my Temp Gauge was acting erratic and moving back and forth just below the halfway mark. After some researched on the site decided the temp sensor might be the culprit

3. Changed the Temp Sensor (the one located) on the Flange

4. Now when my car is turned on from a cold start (after it has been sitting for a while, usually overnight) i notice that the car starts struggles a bit to start up and then starts right up in a warm state? What i mean by this is usually when i started my car after it had sat for a while (usually overnight) The car would turn on and Rev up to about the 1200 RPM level. It would then slowly come down to the operating RPMS of about 800, all the mean while the Coolant Temperature Dial would slowly inch its way to the halfway mark and i would drive off with no problem.

Now my car starts up cold at the 800 RPM Level and the Coolant Temperature Dial stays stuck at C for roughly 20 to 30 minutes (and the Radiator Fan is Running all the while). While i drive like this the car runs really Rough! After about the 20 or 30 minutes the car starts warming up and the dial starts inching towards the halfway mark (at which point the Radiator Fan kicks off and starts working normally), at which point the car starts leveling off and starts to run smoother. I did notice that the temperature dial is still erratic, but not to the point that the previous one was. This one finds its way back to the middle of the Temp Dial a lot more frequently. But still dips below from time to time

Not really sure what the problem is here guys? Could it be that i got a faulty Temp Sensor? Also, when i changed the thermostat housing assembly i didn't have the cold start up issue, only happened after the sensor change?

*Side Note. I have changed my Water Pump and Timing Belt Twice on this car before but have never changed the original thermostat (the one that is on the block) because each mechanic told me that if i wasn't having temp reading issues that i shouldn't really touch it. Well now I'm having temp reading issues, could this be the culprit?

 

Could be the temp sensor although if you purchased from a reliable place and got a quality sensor I doubt that is the issue. Key here is the fan is running when the car is cold. That should not happen. I would suspect the fan control module, but would get codes from a VAGCOM reader and confirm. Not sutre this explains the rough running issue...

 

I did get it from a reliable store. Problem is i probably didn't get a reliable brand. I got a URO. Just going to pay a little extra and get it from the stealership.

I guess ill try and keep it simple. Since it wasn't doing this before i put the current sensor it, common sense would only dictate that a faulty part would make it do this. I guess ill start there.

Once again fan works fine, once car is warmed up. It kicks in and off sporadically when needed. So i think the fan module should be fine. Like i said i think the faulty temp sensor reads the car as already warm after it has been sitting all night hence why the fan kicks is upon starting. Once car is warm its all good. I will exchange and update thread with results.

Any other opinions would be appreciated though.

* BTW no codes are being thrown by VAG-COM, i checked today. No CEL either? like i said the rough running is only when the car is cold. Once it warms up its fine.

 

You hit on my concern if you did not get a "good" sensor. It almost sounds like the sensor has an offset in it that triggers the fan and gives you the erratic running and gage until warm. Smart to start simple and go from there. I'm 50 and after many years doing light to medium maintenance and repairs on my cars, I have learned to trust the manufacturer and their recommendations / parts; they have a vested interest. Notice I said manufacturer and not dealership; some dealerships are good / honest, others, not so much, but then I digressed heavily.

 

Just wanted to follow up in case somebody runs into similar issues with their car. I changed out the Temp Sensor with a new Factory one, and all seems to have gone back to normal. I get the occasional dip but it always centers itself. No Cell, No faults on VAG-COM

knock on wood