I have had my 1999 Explorer for about 9 months and it has run great except for a few small problems recently.

First, when i stop at a light for a minute or so the engine starts to vibrate. Its not an extremely strong vibration but it hasnt been there before. It seems to vibrate for a few seconds then not and then a few seconds then not, etc till i start moving again.

Second, i happened to notice that when i turn the car off there is a slight hissing noise coming from the left (passenger side of the engine).

Not sure if both of these are related or not but it kind of seems like they might be. Otherwise the explorer runs great.

Any ideas?
Thanks.

 

I had a hissing noise come from that area on my 99 too. It turned out to be a bad thermostat, it was stuck closed so the water was getting hot and i guess boiling around the heater core which made the noise. This happened to me for a while due to the short drives I usually take. As far as the engine vibration, could this be your air conditioner clutch engaging on and off, I had the same problem as well. Hope this helps!

 

anyway to make the ac clutch not engage so hard?
anyway to check the thermostat to make sure thats it?