I am still thinking something in the emmissions control system, and I meant engine temp not ambient. In my old Supra I would always get EGR surge but only when it was cold. Even if I am right about the emmissions system, there could be something else exacerbating the problem such as plugs or something. The vacuum hose idea is a good one also althoughg benzdude doesn't say what car he has. My C230 doesn't have nearly as many vacuum hoses as my old car. I think a lot of them have been replaced with electronics.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra