Service Engine Soon Light RPM Increase
 

I have a 1994 STS after driving for 20 minutes or so the Service Engine Soon Light will come on and the RPM' s willIncrease by 500 RPM's. Anyone else had this same issue? Also my headlights will pulsate causing a dimming issuefor about 10 minutes after they first come on. Just thought I would discuss both issues in the same post. Please reply with any info. Thanks