I have a 1999 model with 141,000 miles give or take on it. I've had it for about a year and now the check engine soon comes on then shuts off. It is not consistent in that sometimes it is on for a few days sometimes a few start ups. I would like to fix the issue but i'm not sure where to start. There is also a whistling/sqeal that comes and goes most of the time when the car is first started. It also occasionally pulses (rpms jump back and forth even with no accelerator input). The last time it did this pulsing I changed the tranny filter and that seemed to fix it (less then 30,000 ago). A coworker of mine says that these symptoms point toward the egr valve. Here is what I have done to the car since I got it at a little over 107,000 miles:

Replaced the intake with a cold air system
Changed the oil at recommended intervals
Changed the Tranny filter
Changed the spark plugs and wires (Bosch platinum 4 with Autozone wires- Bosch?)
Changed fuel filter
Changed diff fluid

The fuel filter was stamped with the same manufacture date as the car and the plug wires were stamped 99. The spark plugs may have been original also - could not tell.

I am running to the parts store this weekend but if anyone has any suggestions it would be appreciated.

 

Not sure about the check engine light coming on and off, but wouldn't hurt to get the codes read on it to make things a little easier...

When does it whistle/squeal?

But from my experience, Bosch Platinum plugs were garbage in my car...

 

If you got the extra cash lying around grab one of those code chips that you plug into the car and log onto the computer and it will update whats up with codes with the car.