I was able to find answer to my roblem on this forum with my old Blazer I had and tring to help a friend with his 1997 GMC Jimmy 4wd 4dr 4.3 v-6 .

Jimmy runs poorly, skips, with multiple misfire code when truck is cold. Once truck warms up it runs and accelerates fine. But when cold will not run problerly and any throttle acceleration in neutral or in gear when cold the truck does not run correctly, it will skip and misfire, popping. It still does this after he has changed out plugs, cap and rotor look to be in good shape, MAP sensor, position and temp sensor, tested with exhaust open (catalytic disconnected), injectors cleaned, and swapped out throttle body and coli off a good running truck.

If anyone has a suggeston on what maybe causing the poor running condition when cold I would appreciate it.

Thanks

 

What brand of parts did you use for the tune up? These engines prefer AC Delco ignition components.

Have you cleaned the MAF sensor & EGR valve (how-to's are posted in the tech article section - check the index link in my signature below)? A leaking EGR valve can certainly affect cold performance, but doesn't normally present issues with off idle performance unless it is really stuck open.

Have you had the truck on a scanner capable of displaying live data? Maybe the coolant temperature sensor is faulty and is reporting higher temperatures resulting in a different fuel mix. On a '97, there is a separate sensor for the PCM than what is used for the gauge cluster. The one for the PCM is mounted in the lower intake manifold near the t-stat.