QuestionI have a 98 Mitsubishi Eclipse,2.0L, GSX, auto tranny, AWD and I have been trying to smooth out a rough idle problem. Sometimes while driving the throttle responce is bad, example: I push the accelerator to 50% no increase in speed or rpms just past 50% the car down shifts and is normal. A few times it even lurched once or twice before it got back to having any throttle responce at all. Also I have to push the accelerator to the floor two to three seconds before I want it to respond while getting on the highway (or any full throttle situation). Here is exactly what happens at idle: random puffing and sputtering can be heard at the exhaust after the motor is warm with the sputtering the rpms drop to 200 or below (like it wants to stall) and interior lights flicker from mormal to dim. I have read most of your posts on related problems, thank you, it is going to have the fuel filter replaced on Friday and I have already changed the pcv valve and spark plugs. My questions to you are: Could all of this be caused by a dirty fuel filter? At what RPM should this motor idle at? and How can I tell the difference between an internal problem ( like a bad valve guide) and an external problem ( like a bad IAC motor or a vacuum leak)? P.S. Are there any small tests that I could perform at home to narrow down the problem? Once again thank you for your time and knowledge Mitsubishi owners like myself are greatful! Do I have to register with this site to have my question posted? I would like it to be posted and I was not given an option to say yes.
AnswerBrian,
The first thing you should do is check your throttle cable. It's near (or attached) to your intake manifold. You may see two cables there; one is the cruise control cable. If you run the engine, while in park, have someone step on the gas pedal slowly while you look at the cable.
If you see the cable pulling on the connection to the throttle body, but it's not moving the throttle plate to the extent that the person is pushing on gas pedal, than the throttle cable or cable bracket may be loose or needs adjustment.
If the throttle plate is moving, but the RPMs do not rise up (and they should rise with even the slightest amount of pressure on the gas pedal) then your problem could be with you Throttle Position Sensor (TPS). If the TPS is not position on the throttle body correctly, or is malfunctioning, it can cause this problem. It needs to be checked. Also, a good cleaning to the thottle body, throttle body elbow, and EGR valve should be done. It only takes a few tools and a can or two of carborator cleaner.
A dirty fuel filter can very well contribute to this problem; along with a dirty air filter. Both should be replaced every 1-2 years. Your car should idle around 800 RPMs when warmed up (plus or minus 50 RPMs). Your interior lights will flicker because your engine is not turning quick enough to keep the alternator generating power.
Internal engine problems (like bad valve guides) would cause serious internal engine problems, like lots of noisey rattling coming from the under the valve cover and oil burning out of your exhaust. I would guess your problem is most definitely external. Here's a list of items you should check or have checked:
- IAC (also called an ISC)
- TPS
- Mass Air Sensor (inside your air filter)
- Fuel Pump
- Fast Idle Valve
- Base Idle Setting Screw (BISS)
- Transmission fluid and transfer case fluid levels
- Coolant (make sure it's a nice green color and not rusty)
- Engine temperature sensor
All these items can be check by yourself with a simple voltmeter. You should also pick yourself up a Hayne auto repair manual for your car. They're about $10-$15, and available at more auto parts stores. Below I've also provided you with a link for further reference on how to test most of these items, and how to replace them if need be:
http://www.vfaq.com/index-main.html
That is a VERY informative site and will help you a lot. This question will get posted on the AllExperts site if you leave me a rating. It think it takes a while to list it. Though, I have my own site where I post all my questions within a few days ( http://90gsx.com/eclipse/expert.html ).
Good luck!
