My 99' Max when idling starts to jump or pump. You feel tiny bumps in the car, but only when the car is idling and on Drive. When I put in Neutral I don't feel it anymore.

My guesses would be since the other owner used premium gas all the time and since I got I switched to regular. But, Ive used premium to check if it still does that and it does. I also thought it would be sediment in the gas tank since it would let it get to empty most of the time but no.

Any guesses?

 

Most likely a misfire from weak or failing coil pack(s).

 

change the fuel filter and at least use mid grade. A good start

 

Saving you trouble now. This is the problem. I replaced ALL the coils on my car just to end this problem ( and to know that everything was on top). Before you spend money on anything else check this.

 

What could happen if I don't fix this soon? I don't have the cash to fix this problem. Could it damage my car?

 

You need to figure out the root of the problem first whether it be a fuel delivery issue, an ignition issue, or an air leak

 

Change your maf sensor. I replaced mine two days ago. I had similar problem. If I put the car on drive it will seem like im misfiring but idle was jumping and car shakes with it. When is on neutral or parking I wont feel it at all and the idle doesn't jump. Trust me

 

I bought one on eBay for $45 down here in miami.