P0300 code random misfire on 1998 Chevrolet S10

I change out the ignition coil;fuel filter, wires,PVC,plugs,rotor & cap and air filter,clean thottle body check for vacuumm leaks

by in Friendswood, TX on February 11, 2009
Get Your Car Fixed at a RepairPal Certified Shop.
We certify shops based on expertise, quality work, and verified customer reviews
2 answers
ANSWER by , February 11, 2009
Are you still experiencing problems with how your truck is running? Once a problem has set the trouble code, the light comes on, and a repair is performed. To verify your repair, the code must be cleared. If the light comes back on, you know there is still a problem. To clear the codes: Ignition must be OFF, (Computer can be destroyed if this is not followed), Removed ECM B fuse for at least 5 seconds, re-install fuse.
ANSWER by , February 11, 2009
A misfire code can be set by other things than the ignition. There are three things an engine needs to run correctly, fuel, ignition source, and compression. It's always best to start from scratch first by checking the integrity of the engine. Usually a compression test is enough, but engines that bind have been known to set a misfire code. Once that's established then you can move on to the fuel and ignition sources. If you can read the freeze data see what the fuel trim is doing along with the O2 readings. This can tell you if it's a rich or lean condition. You can also check the misfire counter to see which cylinder is misfiring more than the others. This should give you good information to form a diagnostic procedure.