^+1 ...the answer...end of story.

 

probably.

 

i hope. part will come tomorrow. i will report later

 

...and i will check those hose too.

 

why don't you stop by an autozone today and get the code read.

 

how much they charge for it.!!!?

 

everyone's favorite price...FREE!

They provide it as a service hoping that you'll buy the replacement parts from them.

 

ok. the unstalble RPM problem is now gone after re-install the sprark plug and wires( didn't go away untill couple day later). i am o longer experienced it any more. haven't replace the sensor yet. shipping not coming in untill next week.

will come back and report it later for more details

 

after driving for a week now, I noticed that my car doesn't "drink" to much fuel any more. the improve in mileage is noticeable (about 18 mile per gallon). however, unstable Idle is, again, starting to happen when i drive around for awhile and then park . I will replace the old sensor with the new one tomorrow( took forever to have it shipped).

 

My money is on the O2 sensor. You said that your friend put in "some old sensor". I'm pretty sure that not all sensors are calibrated equally. They may (and probably do) send back a voltage level that is different that what the "8" is expecting. They may also have a different "change factor". That is to say, while the RX's O2 sensor changes its value by say a 1% voltage change at a certain 02 reading, another may change its value by 5%.

Why would this cause erratic idle? The ECM sense a lean situation and adds more fuel to the mix. The 02 sensor detects this change and reports back to the ECM. The ECM detects a lot bigger change than it should have been and leans the mixture out again. Repeat ad nausium. Why it doesn't do it all the time... haven't a clue. This is just a theory from an electronics guy. Hope your new sensor fixes the problem.

 

problems solved. replace sensor and everything went back to normal.! thanks guys