Ok. This what I have going on. I have a 1998 4 door 4x4 ls 4.3l. This blazer just had a reman installed from jasper around the end of march 2013. Upon receiving my vehicle the check engine light came on. Original installer scanned the ses and came back multiple cylinder misfire. They did not repair since I was moving 1300 miles away the next day. Vehicle in tow I arrived took to a mechanic and they said they could not find any codes that match what the other mechanics found, they checked timing and corrected it and put a new router gear in, check light came on the next morning after what they did. This condition only occurred during colder weather. When it gets warm the code clears and everything runs fine. When cold rough idle then goes away when engine warms up. No more funds is the reason I didn't take back to mechanic. FYI autozone code reader said cylinder 5 misfire after the timing and router fixed. Hope I got the right thread.

 

Also gas mileage sucks. 11mpg and I did a 0 to 60 in 14 seconds. That seems really slow

 

The rough idle only occurred during cold weather. When it is 50 or above everything runs fine minus the mpg. Also motor sounds like a typewritter is this normal