2000 Mitsubishi Eclipse • 175 miles

I'm having an issue with a rough idle along with my gas mileage dropping about 50%. When I start my car first thing in the morning, it will turn over and sometimes stall, or the RPMs will drop low enough where the interior lights illuminate for a second, but the RPMs will go higher. And then back down again. This process will repeat itself until the car warms up. If I press on the accelrator, the car sputs and sputters at first, but reacts normal once the car warms up. Once warm, the car idles as advertised. I cleaned the throttle body, and this helped alot, but has not fixed the rough idle I've also cleaned the Idle Air Control Valve, MAP sensor, MAP sensor, throttle position sensor and I've changed my EGR valve. I've looked for vacuum leaks and haven't found any. With the car running, I've sprayed Carb cleaner all around the engine to try and find a vaccum leak, but nothing. After all this, I dropped some SeaFoam in the gas tank, followed by some 93 octane to a full tank, and, as stated earlier, the car will run/idle fine once warmed up. But my gas mileage is terrible. I normally get about 300+ miles to a tank. I'm at half a tank, and havn't even reached 100 miles yet! I think my IACV is bad. I will diconnect it, start the car, and it will idle at approx 1200 without a hicup.I'll turn the car off, connect it back up, start the car, and the rough idle returns, but could the IACV really be the cause of such a drastic change in my fuel economy? I've also pulled my plugs and to make everything even more confusing, it seems the car is running lean. My plugs had a chalky, greyish look to them. They were not "wet" at all.
Ken Benson
February 28, 2012.

The first thing to do would be to get the trouble codes pulled. Any Advance Auto or Auto Zone will do this for free. That will help you out a lot.
The things that I would be suspect of that might not show up on a code test are the fuel pressure and maybe a bad O2 sensor. O2 sensors usually will come up in a code read, but what you are describing is either that or an exhaust leak near an O2 sensor. The leak lets extra air onto the senor so it thinks the eninge is running lean and it dumps more gas in it. So look for exhaust leak, test the fuel pressure with tool which you can borrow from Advance or Auto Zone and pull the codes.

There are two codes p0100 and p0403. I can't remember which was which, but one called out the EGR valve, which I changed, and the other called out either the MAP sensor, MAF sensor, and vacuum leak. Nothing about and 02 Sensor. Although, I have had a code for an 02 sensor in the past. By the way, these two code were pulled after I changed the EGR valve. Thanks for the quick response! I think the IACv with fisx the idle problem, but not the gas guzzling problem. Thoughts?

Ken Benson
Feb 28, 2012.
P0100 is Volume Air Flow, VAF and P0403 is Exhaust Gas Recirculation Return Solenoid Malfunction, EGR.

You might try to clean the MAF with some MAF cleaner, but be very gentle as they are senitive. Again look for a vacuum leak as that would cause poor performance and gas mileage and check the EGR pipes around the exhaust. There may be a leak in the system causing the same sort of issue as with the O2 sensor.
You may have braoke something loose when you did the EGR so re-check your work and look for any metal along the pipe that may have been rusted and it gave way when you replaced it or simply dis-connected.

Thanks for the help. I'll look for the exahust leak and see if I can find anything. I'm confident I didn't break anything while changing the EGR. It was fairly simple to change, although the location was a pain (between the engine and the firewall). A small vacuum line, 2 small coolant lines, two bolts and the gasket. Although I don't work on cars, I do work on airplanes, so my maintenance practices are the same.

Ken Benson
Feb 28, 2012.
If you work on airplanes you must be EXTREMELY thourough. I used to work for DOD when I lived in DC and I did some work with F/A-22 and F/A-35. Pilots love the F/A-22 and of course would rather have two motors. The 35 is an impressive jumper though.
Good luck and let me know how things go and we can go from there.
Sometimes when a car has quirks that are hard to diagnose, going to online enthusiast forums are a great source. My GF had a 2007? Spyder and if it weren't for pics on enthusiast forum I would have never gotten timing belt done. Forum members go to a lot of trouble to take pics and type up walk throughs with them and work arounds. I want to say it was a 3DSM forum or 3rd generation eclispe or something like that. Anyway it was the best help because it was a bunch of people who live for the car and have seen it all including the hard to diagnose quirks some cars have and you can post and they are happy to help you or direct you to an old post.
Just a thought as it is a good thing to know for any Eclipse stuff. I will try to find the forum if I get a chance.

Thanks! I like to think I'm very thourough. Thats why at times like these, when I am beyond my capacity of what I know, I get frustrated. I know the car is getting too much fuel, thus the 50% cut in mileage. My mind understands that, but its the figuring out 'why' part that I get stuck. Like you said, something is telling th car computer to feed it more gas. But what part is telling it to do that? I know that if the car runs a certain way, and then runs better when I disconnect the IACV, that tells me its bad. UGH! I'm ready to change the MAP, MAF and the IACV at this point, but 2 out of the 3 have a hefty price tag on them. So I don't want to just start changing parts, without the confidence that one of the parts will fix the vehicle. Thanks again for your help. I won't be able to get 'under the hood' again till the weekend, so hopefully I will have sopme good news to report then. Btw. Where you 'used' to work, you hit the nail on the head! 15's and raptors!

Ken Benson
Feb 28, 2012.
Yes the Raptors are awesome.
When you get back to me tommorrow I will get a IACV test instruction set for you. It is actually simple. You just disonnect it with the electrcis still connected, sometimes coolant lines too, have a buddy turn the key and see if the solenoid/plunger moves. If you have not cleaned out the portsfor the IACV, it may be a good time to clean that and the trhottle body. When you do so always spray cleaner from the outside into the intake manifold so you don't cram deposits further into the ports. You might also need to check or replace the TPS if we have not discussed that. I will get with you tommorrow and get a fresh look at it. After 50 or 60 questions I kind of get them all muddled together.
I will reply ASAP when you post.

I want you to have this link on a Vovlvo I went back and forth with forver until it got straight. It hink the MAF is more of a suspect the more I think about it. After you read this, I remembered it as I was logging out, you might agree or dis-agree. Let me knwo what you think.

I have read about that IACV test, but haven't tried it yet, but its definitly on the list of things to do. I'm very curious about it. Thanks. Is there a similar test for the TPS? I don't have a multimeter at the house, so my testing abilities are limited. I think I'll start with what the car is throwing at me via codes. EGR solenoid (p0403), and the MAP/MAF sensor(p0100) and go from there. I do question the integrity of the MAF sensor. While the car is running, I can tap on the top of the sensor, and the RPMs will change. I read the thread concerning the Volvo. What kind of test did he do to figure out the root cause of the loose clamp on the intake?

Ken Benson
Feb 29, 2012.
There is a voltage test for the TPS. There are three terminals on the TPS. I forget which two you put the positive and negative on, but you will see that pretyty easy. If you get the polarity wrong most multimeters just read negative voltage. When the TPS is closed it sholud read.5 Volts and at WOT it should read 4.5-5.0 Volts. Not all are adjustable. If you get a replacement BLOX makes an adjustable one. If you ever need aftermarket stuff, go to horsepwoerfreaks. Com. If you get the right person they will remember me as I still talk to them. Not for parts as I don't have my 1990 Integra that I put a 1998 GSR JDM Motor and trans in. I totalled it. Just some bolt ons and an adjustable fuel pressure regulator with an AEM Air/Fuel ratio EUGO meterr for tuning and it was so fast. I beat a new mustang by a few car lengths. Then I got beat by an S2000, not a surprise. I did not have the redline set properly though, I was shifting at 6500 RPM and I set it to 8500 where it should have been and it pulled so hard all the way. I had it going 120 in third gear with a few RPMs left. Pretty sick but it takes a lot of HP the faster you go to gain speed so I guess it would have done 140+ or so. I don't remember the accident as I hit my head a few times. It looked like it bounced between the bash and the steering wheel because the wheel was bent backwards and I had a bald spot on my head in the shape of the steering wheel, I am so glad it grew back. I really misss it and the guys at HPF are real enthusiasts and are like having a Tech support person and Sales person all in one. They will give you EBAY prices if you ask too. Anyway, be careful when you drive because all I could have done was to have been messing with the radio or lighting a cigarette and where I went of the road was a drop off so I could not avoid the telephone pole I hit. In a fast car sometimes you don't realize how fast you are going. 55 MPH is slow in a 140 MPH car and you would not believe how I got cut wide open by the seat belt buckle. Think about the force it would take to cut someone open all the way to there abdominal cavity with a belt buckle. I have a scar across my chest from the seat belt. I know I am going on about me but whenever I have a customer with a fast car I just feel kind of obligated to tell them how quick things can happen as it does not take much pedal to get going another 20 MPH unlike other cars.
So, The BLOX TPS is slotted for adjustment. I actually found TPS adjustemnt in our manual. I am attaching instructions and FIG4 which is the pinout for the connector. If I captuered the MIRAGE stuff, just ifnore it, you don't need FIGs 5 and 6.
I found EGR tests and have FIG for them. The only MAP info I could find is to check for vacuum leak between it and manifold.
So, I am attaching all said stuff and the files are labeled and are jpegs.

Page 1 of 4