1995 3.3L Bad O2 Sensor?
I got my 1995 3.3L Intrepid about a year ago, and it's ran pretty well since then. Except for a few issues:
1) It has an issue where it has sudden RPM drops when stuck idling (and fully stopped) in gear for long periods of times. Experienced this twice since I got the car, once about 9 months ago, then again 5 months ago. I now throw the tranny in Neutral at long stops to avoid this issue happening.
2) The car makes a grating/clicking noise when accelerating from a stop. Seems to only happen in the 1000-1400 RPM range. Very brief and goes away once a speed of greater than 10KMPH is reached. Also, when idling in gear, noticeable vibrations occur that will stop as soon the car moves or is thrown out of gear. Replaced the tranny mount, as I suspected it to be the issue, but it didn't change anything. The issue started about 6 months ago when I was driving on the highway and suddenly what sounded like a loud blowing noise occurred (I thought maybe my tranny or engine had blown), but the car kept running fine, and I pulled it over, did a "key dance" and got only code 5-5.
These two issues seem like no big deal, but then tonight my parents were driving my car and reported that they got CEL (check engine light) warning after about 10-15 minutes. They were almost home, so they drove it home and reported the issue to me. I checked it out, and as far as I can tell, the light only comes on when the car is fully warmed up and at operating temperature. I notice no change in the cars performance compared to yesterday, so it's not like it's something major, such as a transmission/engine failure.
The car is running relativity fine, although a few weeks ago I noticed the occasional "hitch" on the highway after extended periods of maintaining 80KMPH, it was like disengaging the clutch and dropping it again very quickly in a manual car at that speed. It happened maybe twice in a 10-minute highway stretch. Also, it seems like the car has been using more gas (I'd estimate around 25% more) for the past month, I'm not 100% sure if this is a symptom, since I don't keep track of my gas mileage, but I just have a hunch about it. I never had to fill up this often before, and I'm not really driving any farther.
I did the "key dance" and got the code 1-2 2-1 4-1 5-4, for some reason there didn't seem to be a 5-5. I'm gonna re-do it in the morning, as I'm not 100% on that code.
In conclusion, I suspect my O2 sensor(s) may be faulty, but I'm not very good with cars. Does anyone have any idea what could be wrong, based of the info I have here? Am I on the right track with an O2 sensor malfunction?