96 Achieva p0442/p0300

[daverr]

Hiyas,

First I would like to thank you in advance for your help and time. I own a 96 olds achieva 2.4L automatic with 135,00miles, All of a sudden out of nowhere it started misfireing when a friend of mine and myself hooked it up to the computer we got theese codes (p0442 evap control small leak) and (p0300 misfire detected). The check engine light has been on for quite some time now it randomly goes on and off im not too familiar with the comp. systems in this veichele but was told when i talked to a few people that the p0442 code could be set off due to a faulty gas cap normally a 0-ring or a rusted tank stem where the cas cover screws on? This car has been brought to a few shops and without the knowledge of the code i have always been told that the problem was solved by replaceing this and that sensor and them reseting the code and anywhere from 4days to approx 2weeks later its back on, Is there anything else i should be looking into that would trigger this? The second code that comes up is a p0300 misfire code im told that this is a generic code that is not directly related to a specific problem and leaves the problem open to a variety of things. Recently this car was brought in for a tune up November 8 of '06 the air filter,gas filter, sparkplugs,wires, and coil cover were replaced. Is there anything else i should be looking into that could cause this problem that wasnt replaced already, or could something that was replaced have gone bad to cause this?Once again i would like to thank you for your help in advance

[BNaylor]

Welcome to AF.

The P0442 odb-ii DTC is the worse evaporative emissions fault to have. It is a small leak detected. It could be anything. Leaking evaporative emissions lines at the fuel tank, to engine at purge solenoid, cannister, fuel tank seal, etc. See link below:

http://www.automotiveforums.com/vbul...d.php?t=622473

DTC P0300 is random misfire meaning it is not limited to any specific cylinder. If you did not have the DTC before the tune up then those parts could be suspect. What brand spark plugs or ignition components were used?