Hey all, just recently bought a 99, my second blazer, noticed it was running a little rough on warm start until it was running for a few then was fine, tested fuel pressure, turned out spider was leaking into plenum... So I look online, and at this time I couldnt afford a new spider so I found a used one (I know, one thing you should never buy used, but this one was barely two months old, guy had just upgraded it then got t boned a few weeks later, still has receipt, and I got it cheap) Today got it installed, new plenum gasket, throttle body gasket, no vacuum leaks, tested fuel line for pressure and was good, started it up, ran beautiful, very smooth. Took it for a drive, came home, and noticed it was idling rough... Not extremely rough but noticeable. So i sprayed some carb cleaner around spider and plenum, no noticeable difference, and its not throwing any codes whatsoever. Now it's not running rough enough to really see a difference with carb cleaner. I can't see it being the spider, because it ran beautiful up until i drove it... Theres no issues with acceleration, no hesitation. Any ideas?

Only thing i didn't try was cleaning the IAC, because there was no problem before...

 

Exactly what was the difference in the way it runs before/after your repairs. This is not clear and is probably why you are not getting responses.

 

Ok so the original problem was after it was warmed up, once you try to restart it, it hesitated to start and once it was running ran real rough for a few minutes and then ran pretty smooth, aside from the warm start it was fine. Tested the fuel pressure and discovered the spider was leaking, so that's when i got the mpfi spider, and on first start with the new spider, ran beautiful, up until I drove it for about 10 minutes, now has a slightly rough idle with no codes.... Now this morning i discovered that its not warming up very well... Only reached about 150... Im not sure if that may be part of the prob or not. So basically idled good aside from warm start before, now idles a little rough after...

 

Please plot maybe 15 seconds of short term fuel trim values for both the left and right O2 sensors while the rough idle is occurring. This will tell you if you have any problems with the fuel mix being lean as the cause. Fuel pump, IAC, vacuum leak, whatever.

 

Well it turns out you can't fix stupid. When installing the new mpfi spider, i used the old bracket to mount it, which is bigger than the new one, so it was pinching fuel line for cylinder 5....

 

Glad you got it fixed

 

why wont a code reader work on my 1995 chevy blazer with 4.3 4x4 it comes up with error this runs really rich