QuestionMy vehicle runs fine when first started but after it warms up it begins to get a intermittent miss at idle and at cruise (any speed). I already replaced the fuel pump,fuel filter,full tune-up,TPS sensor, and ignition module. My check engine light only blinks a code for the O2 sensor, but I don't think that would cause the trouble. It also lacks in power since the problem evolved.
AnswerHi Kevin,
The O2 sensor probably doesn't cause the problem as much as its correct reading might.
If the exhaust is rich, the sensor will register that, send the info to the ECM, which in turn will lean it out.
Sensor readings are not used until after the engine warms up, which would explain why it runs better cold.
I have needed to replace plug wires on an S10 to correct that, but you may have already done that.
Some injector cleaner through the tank can help.
Also, make sure the air filter is clean, and rodents haven't built a nest in the intake plumbing.
Weather your problem is sensor/closed loop related, or heat induced electrical resistance related will just take some more searching.
Mitchell manuals usually have a pretty good section on sensor testing that can reduce the expensive game of conclusion jumping and parts replacing, but some time is needed, and sometimes the tests are hard to understand, but they are usually pretty step-by-step.
A little Haynes Manual from a parts house has the same thing.
Vacuum leaks, even very small, are not measured by air intake sensors,(MAF), and even if all the sensors are working correctly, the lean mixture that results from the unmeasured air can cause a small ping, or knock, which the knock sensor will register,(correctly), and tell the ECM to retard the timing, etc.
So keep after it, and I hope this gave some ideas.
Van
