what causes rough idle on cold engine no stall

Asked by Dec 20, 2013 at 01:55 AM about the Volvo 240

Question type: Maintenance & Repair

Just bought a 240 DL with 82,500 garaged miles. This one is a keeper. However it has rough idle on cold start with a service light. Idle smooths out, service light goes out when temp reached.Service light is on with every restart and goes out in a few minutes. Does not stall or misfire. Ideas?
It also has a mild ping when engine is taxed climbing a hill. Anti knock valve?
Any ideas will help.

3 Answers

223,485

That should your first indication there is a problem. The Service light doesn't pop on for no reason. Have the car looked. Might be a simple vacuum leak due to the rough idle and pinging.

Thank you. Of course a service light is the best indication of a problem. My goal is to try and figure the problem out before taking it to a garage. I read from another that his 240 did the exactly the same. It was rough for a year on cold start only. After the year, car started to stall. It turned out to be the coolant temp sensor sending a bad message to the cold start device causing it to kick on too early. I will check for vacuum leak first. Great place to start. Is it (how is it) possible for a vacuum leak to exist when cold only? What other parts could cause this so I can check and test them?

The service light that comes on, then goes off, that is the program stating you have gone around 3,000 miles, and it is time to change the oil. To reset that light, you have to take the speedo cluster out, and reset it with the switch/button behind the speedo. The light comes on when you first start it, then goes out after two minutes. You can see instructional on Youtube. Rough idle, did you check your air box thermostat? When they go bad, they only suck in air of the exhaust manifold. We have done this to our 1992 240, and it has helped a lot. We also took the throttle body off, cleaned that with carb cleaner, and re-installed it. Runs great, now.

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