I had this problem on my 1996 Volvo Turbo ever since I got the car - over a year. I also have a 1994 Volvo Turbo and didn't have any problems with this. Couldn't figure out what was so different between the two.

Then recenly I wanted to check the condition of my air filter. I opened the filter box and the air filter was not in place on the bottom part of the housing - it had been lifted up into the top half of the plastic container holding it. It was blocking the air intake with the grill towards the MAF sensor. This was also having detrminental effects on my turbo performance - it was starving for air - very slow response. I held down the air filter as I put the top plastic cover just to be sure that it was not going to move out of place. Now my RPMs at start are always under 1500 just like my 94 - before they were more like 2500.