Mitsubishi Eclipse 3G Club banner

1 - 6 of 6 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
Hey everybody,
I’ve posted here about this before, but the issue is still here so I thought I’d post again. My eclipse GS (150k miles) with the 4g64 idles at 3000 rpm on startup, and about 1900-2000 after a few minutes. When the wheels are spinning and either the clutch is in or it’s in neutral, the idle bounces between 2000 and 2500 rpm. Here’s a video.
Here’s a list of parts I’ve already replaced (in order of when I replaced them):
  • Idle air control valve
  • Mass air flow sensor
  • Throttle position sensor
  • Throttle body gasket
I’ve also taken the throttle body off and checked the inside of the intake manifold for cracks since someone said that’s common with the 4g64. I didn’t find any cracks, though, and I had a mechanic smoke test the car and they couldn’t find any leaks.
The only thing I can think to replace at this point is the O2 sensors, but I don’t know how to tell if they’re bad or not. Here‘s a picture of the top sensor.
So two questions: can you tell if my O2 sensor is bad from the picture, and what else could be causing my high idle? Sorry to post about this for the third(?) time, but I’m getting pretty desperate.
Thank you for your help!
 

·
Registered
Joined
·
5 Posts
Your service engine soon light is on, what are the codes? Those would probably point to the problem. Don't think it's possible to know if an O2 sensor is working by visually inspecting it (unless the wires are torn). Assuming you have an OBDII scanner to check the codes for your SES light, you might also be able to enter the live data function and check if the O2 sensors are functioning by checking the voltage, they should all be oscillating somewhere between 0.100V to 0.900V. 0.000V would indicate a bad sensor. If they are near 0.100V then you are running lean (Too much air or too little fuel). If they are near 0.900V then you are running rich (too little air or too much fuel). Lots of things can cause idle fluctuations like that. Use an OBDII to narrow the source of the problem.
 

·
New To Site
2001 Spyder GT
Joined
·
245 Posts
This is a gremlin I have been fighting with also .. In park it idle`s between 1500-2000 rpm`s but in gear it goes to normal around 1000 - 900 rpm. With the mass air flow disconnected it run`s perfect... ?
 

·
New To Site
2001 Spyder GT
Joined
·
245 Posts
If you are talking about the adjustment at the end of the throttle cable ... mine is down as far as it can go.. Now as far as the Biss screw goes I`m not sure if it`s in the correct position.. . This is @pigroy post so hopefully he has checked these also....
 

·
Registered
Joined
·
9 Posts
Checked some papers and found these as a potential causes of high RPM:
  • Sticking throttle cable (try moving butterfly valve by hand with cable detached)
  • Engine coolant temperature (ECU and dash needle use seperate temp sensors, you should check if engine is seeing correct temp. Do that with OBD scanner. Perceived low temperature causes high rpm.)
  • Idle air pasthrough mechanism (blocked heater pipe / vacuum leak / debris / faulty actuator. All unlikely, yet plausible)
  • General vacuum leak (any air entering intake manifold after the butterfly valve will increase rpm significantly. smoke machine is your best friend here)
  • Air conditioner on with empty loop / power steering pressure sensor (A/C and power steering systems are monitored by ECU and can increase RPM if extra load is reported. Although this is normally only about 300 to 500 extra rpm)
  • Throttle position sensor (faulty readings here will make ECU think that accelerator is being depressed. If you have a multimeter these are just regular potentiometers)
Hope it helps
 
1 - 6 of 6 Posts
Top