Volkswagen Passat Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter #1
So my 2005 V6 Passat has had a hard time starting it left sitting in the cold for a few days in the past. I’ll start it and it’ll be fine hen but a rough start. Sometimes it’ll be tougher and it’ll run rough until I turn it off and back on. Today I went out after it sat all weekend and didn’t run at all. Uninsulated garage and running into the 20s at night. It took about 15 tries to get it started and then ran rough until it warmed up and I restarted it. I’ve already done the alternator a little while back. When it cranked it was really cranking too. Battery? Something else?
 

·
Moderator/Administrator
Joined
·
24,583 Posts
the Coolant temp sensor is the first thing I'd check/replace. Do you have a bluetooth/Wifi scanner or VCDS? Most free phone apps can read coolant temp. Android has a great one: Torque Iphail users (I'm one of them) "Car Scanner" or "Car doctor" aren't bad.
 

·
Registered
Joined
·
27,421 Posts
How old are the plugs and are they NGK? Is the CEL on?
 

·
Registered
Joined
·
18 Posts
Discussion Starter #6
At least 5 years old(how long I’ve had it). Sorry not sure what NGK is. My CEL is on. Has been for a while before this though. Initially thought it was the broken flex
Pipe I had fixed.
 

·
Registered
Joined
·
1,253 Posts
NGK is the brand of spark plugs. Some Passat engines are 'fussy' about the type of plugs in them and run better when the correct plugs are used.

If you have any OBDII reader I'd try to read the coolant temperature when the car is cold. If the temp sensor fails (a common problem) the engine computer won't know the engine is cold and won't supply enough gas for the engine to run right when it is cold. A cold engine needs a much richer (more fuel per air) mixture than a warm engine. If the temp sensor fails, the computer will just pick an average temp value which probably won't work right when the engine is very cold.

Can you read the CEL codes with your OBD reader? You can either post all the codes or better yet, clear all the codes and see which ones come back.
 

·
Registered
Joined
·
2,057 Posts
agree that it is probably coolant temp. sensor , someone could chime in here, but if you disconnect the sensor bonnet wouldn't it imitate conditions of a bad sensor ?
also would not hurt to clean MAF sensor,assuming you have a lot of miles on the car given the year
 
1 - 9 of 9 Posts
Top