My volvo 740 has 254400 miles. I have had it for 4 years. It has been great. I am disabled and live solely on my SS check. Last week when I started it the engine started reving up and back down then up and down on its own. I took it to my mechanic who to date has always solved my problems and he changed the flow meter, valve sensor, and colltemp sensor. He got the parts from junk yards because he knows money is tight for me. Parts were $170 labor $130 and he let me drive off. Well the problem is worst then it was. It does it (engine idles up then down continuously) not only when yopu start it but now even after it is warmed up. Also if you put it in neutral and step on the gas it idles up and stays up for many seconds before coming down, and lastly driving today I stepped on the gas and it barely accellerated. I do not think my mechanic knows how or what to fix and everything he did so far probably did not need to be exchanged. Please help me. Marl Binda