i have a 93 vigor and sometimes when i am at a light i will feel a jump type feeling come from the car, the idle will jump down then back up to normal in like a second. sometimes it only does it once and sometimes it does it a couple times a few seconds after one another.. and when the car is warming up, the idle goes down then back up a few times, not fluctuate but goes down some then back up to where it is warming up.. any help.