Re... 2002 Blazer Extreme

I've got an '02 Extreme Blazer and the SES light is on. It's been on and off for about 4 months now. I was originally told that bad gas was probably the problem, so with some gas treatment it would be solved. After adding the treatment, the light would eventually go off in a day or so. However it would return in a few weeks. This time with new symptoms. Here they are...

1. When parked and idiling, it idles roughly and threatens to stall completely.
2. When first cranked up, it idles very high.
3. After cranking, when I put it in reverse, the engine stalls or threatens to stall.

The SES light will come on and off at various times sometimes on for days then off again, only to return another day. Can someone give a diagnosis for this or any suggestions?

Thanks!


Went and got the PCM scanned and there were no codes given. The SES light was on when they scanned it, but then went off when we tried it the second time. Still having same issues as the above paragraph details. Any suggestions as to the cause of this?

Obd11 sans and code readers do not tel all
Get it on a engine/transmission capable scanner.
Check for past/history /present or pending codes.
Post back code no. from a good scanner.