Our 2002 Volvo V40 has developed a problem. It will start, but only if you give it gas immediately after turning the ignition. Then if you let your foot off the gas, the engine dies. There are no warning lights on. I drove it home when this started by keeping one foot on the gas and another on the break to regulate my speed. What might cause this problem? On its last tank of gas it got 27mpg, which is pretty good. We had just filled it up with premium, as it has no ethanol. I tried running some engine cleaner (Lucas Tune-Up) through. I ran it for about an hour at high rpm. It still dies at idle.
There may be a vacuum leak or restiction in the air intake causing this problem. If there is an idle control valve that may have a problem.
It could have a low idle, especially if you have a dirty air filter or a bad mass airflow sensor.
You might try spraying some carberatur cleaner in the throttle assembly. If you try this make sure you follow the instructions on the can.
Had the exact same issue with our 2001 V40 and oddly enough I also tried going for a long drive with premium and Lucas in the tank, which didn’t help here either. It turned out to be a faulty mass air flow sensor and fuel pressure regulator. Local Volvo shop installed new parts and the car starts up much faster and runs fine now.