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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 6953
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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2003 eclipse rs 4 cylinder. sometimes throttle doesn't work,

Customer Question

2003 eclipse rs 4 cylinder. sometimes throttle doesn't work, fully depressed on goes to 2000 rpm. Happened a few times goes away then comes back. Right now it works except check engine light showing 421 in processe of changing downstream 02 sensor. Don't think thats anything to do with throttle because its working right now.
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.

Hi,

What is the reasoning behind changing the O2 sensor? The P0421 will not set as a relation to that sensor without either (1) there being other faults related to the sensor or (2) being an incorrect (like Bosch) sensor to begin with.

Knowing that the catalyst is registering a fault, has the exhaust been flow checked to make sure it is not clogged as that would cause every one of your symptoms.

Customer: replied 1 year ago.
because I have message p0421 but thats not my problem. throttle working fine now throttle is intermittent problem.
Expert:  Doug replied 1 year ago.

P0421 won't be related to the O2 sensor... that doesn't happen on these cars without either an additional fault (O2 no activity, for example) or there being incorrect sensors installed to begin with.
Auto parts stores love selling those for this because they stock the sensors and not the cats, but on a Mitsubishi you will pretty much never see this code mean a sensor except in the two previously mentioned capacities.

How often does the throttle response issue occur? Can you match it to any specific circumstance (like only after driving a certain amount of time or distance, only at certain temperatures, only with a certain amount of fuel in the tank, etc)?

Customer: replied 1 year ago.
No it has been ok for a month. I think a rapid throttle input can cause it but not sure. I can have peddle on floor with only 2000rpm. If I slowly depress throttle I can get it to go higher. That's how I got it to stop once slowly accelerated to max rpm then worked normal. That other message came on recently but not during throttle problem just coincidence I guess .
Expert:  Doug replied 1 year ago.

Whenever you have a scenario like that where you get the pedal to the floor and you are unable to increase speed you are really looking at either a fuel control issue or an exhaust flow issue.
Nothing spark related is going to do that (well not without running absolutely awful and setting misfire faults etc); compression would, but it would not come and go so that is out. The throttle body/cable could, but likewise it would not come and go.

How long did this condition last for? More than one tank of gas (and perhaps there was some contaminant in that tank full)?

Customer: replied 1 year ago.
What about engine computer. My mazda truck was running bad to good couldn't find anything mech said it must be computer. Change engine computer been fine ever since.
Expert:  Doug replied 1 year ago.

Mitsubishi computers do not behave like that; when they fail they fail for good and don't suddenly start working again.

Luckily it is rare to see them fail anyway.