Hi all,

My van's Check Engine light has been staying on a lot lately. It used to only come on occasionally while driving at highway speeds and would shut off if I shifted into neutral and coasted for a little bit. (It's a one-owner van and did this ever since it was brand new.) Now lately it is coming on when I start the van and while driving in town. It only goes off when accelerating up a hill.

I haven't driven at highway speeds for a while because I need to change the thermostat and haven't had time to do that. How do I figure out what's wrong? It's an '87 5-speed, and it's been raining all the time here lately, too (in case these items matter).

Thanks!