Questions and Answers

Volkswagen Jetta Runs Rough Q. Vincent, After reading your replies to many interesting Jetta problems I'd like to ask you a question that has been stumping myself and many mechanics over the last few months. When I start my car after being idle for at least 30 minutes, regardless if its cold or not, I notice the temperature needle does not move and my car runs accordingly.

As soon as the needle begins to rise which is approximately 8-10 minutes after driving, the car begins to tremble and vibrate, feels as if the gas is not flowing fluently or the car is not breathing properly and is struggling, so I let go of the gas a bit, then I step on it again and the car runs with no trembling, two seconds after, it begins again.

In the last month, I have changed my timing belt and my oil, the problem began about three months ago, but it has gotten worse, It wasn't as heavy as it was in the beginning. Can you HELP??

• 1992 Volkswagen Jetta
• 1.8 liter
• Manual Transmission
• 180,000 kilometers
• Fuel injection

Thanks so much,
Mario
Montreal, Canada

A. The most likely cause is a bad Coolant Temperature Sensor (CTS). So that would be the first thing to check.

To check it, unplug it and with an ohmmeter check the resistance. At 70° it should be about 2500 ohms. At 50° it should be about 3500 ohms. If not, it will need to be replaced.

Harness connector shown disconnected from CTS (arrow) on models up to 1989 (top) and later (bottom)