Hi everybody!

yesterday i had problem with the acceleration of the van. When i'm driving, go at a constant speed of 60 miles/hour, then i release the gas pedal for maybe 1-2 seconds, and when i try to push again the gas pedal to maintain the speed at 60 miles/hour, engines have misses. I have to push down the gas pedal in the floor to bypass the problem.

In a stationnary mode (warm engine) , the problem come when the engine is idling around 1800-2000rpm. The idle is perfect at +/- 750 rpm. the problem is when i gradually increase the gas pedal. the rpm increase constantly, but when it reach 2000 rpm, the needle go back to 1800 rpm, then 2000rpm, then 1800 rpm etc... to bypass this problem i'm pushing hard the gas pedal and the engine rpm go 3000 rpm and over, as usual.

can someone help me with this?

The van is used maybe once a week. the gas tank was less than the half (maybe water formed here in the gas tank when temperatures is low like -25 celsius. i forgot to fill it to avoid condensation in the gas tank)