I have a 97 eclipse that has a rough idle and is running lean. My friend, who is a certified mechanic, ran a diagnostic check on his computer and found that the car is running really lean. However at higher RPM levels the motor seems to even out and run ok. We have changed many different sensors to try and remedy the problem but still cant figure it out. Here is a list of what i have changed so far.

MAP sensor
Throttle position sensor
EGR valve
Front O2
Rear o2

The car has a header, resonator in place of Cat, and magnaflow muffler.
I know I am a new member, But any help would be greatly appreciated. I have big plans for this car.

Do you have ay diagnostic trouble codes (Check Engine Light)?

What basis did you use to replace the above sensors? Unless there is an indication that a sensor is faulty (OBD II DTC) I would not start throwing parts at it - you will only waste your money.

Check for vac leaks? Cleaned throttle body? Check the IAC?

Start with the codes, if any, and go from there.

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2012 2500HD LML

There is and always has been only one code that comes up and that is an evap code, we have checked for vac leaks and found nothing. I changed TPS because it was reading like 12% at idle. o2's Cause they where never changed and they seemed like a good place to start, o yea I did Have a code for no signal from front o2, but this did'nt change anything really as far as the overall problem. He also told me that the MAP was reading kind of funny.

So I'm not really just throwing parts at it.

Thanks for helping though

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2012 2500HD LML

Cant figure out whats causing it. But it should have nothing to do with the lean condition. Right? like i said we hunted all over for vac leaks changed vac lines, checked for gasket leaks....?

I did clean the Idle Air Control. Also i have another used one out of a parts car. Should I try it? Could TB be worn and causing it? It just doesn't make sense that at higher RPM it starts to run right,like around 3500. Its hard to explain. When you hold it at a steady RPM, say 2000 it kind of sounds like a miss, But we figured it was from inadequate fuel, like fuel cut, since the diagnostic comp says its running lean on all cylinders.

Unless you are looking at actual injector pulse widths to determine that it is a fuel problem, you should also consider an ignition problem. Misfires will show up at lean conditions to an oxygen sensor as there is unburned fuel/air in the exhaust stream.

Check the usual: plugs/wires/coil/pigtail etc.

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2012 2500HD LML

ok I will Check. I didn't think about that stuff. However it does have new plugs but i will check anyway.

Thanks

Any exhaust leaks? Check for those (even if you can't really hear it), as it'll pull air in at low speeds until the high-speed flow/pressure is enough to push it out. Will throw O2 readings off - my DP has cracked on me twice and have seen this pretty evidently

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'95 GS w/ t3/t4b
FMIC, diy piping & RFL BOV
MS2-Extra Fuel&Spark
50 lb/hr Holley injectors w/ 1:1 RRFPR
JE 8.8:1 dish w/ Hastings Rings
Eagle Rods w/ ARP bolts
ARP Head studs
Mild port/polish head
3" custom DP/cat section, 3" PIT catback
dual MBC - 12 psi / 20psi

You mentioned above that you were seeing a code for no signal from the front 02 sensor. I know you said you changed the sensor. Did the code go away or is it still there? The front 02 sensor is responsible for adjusting A/F so if there is an issue with that signal the car will not run correctly.

As for the EVAP system leak check three things: 1. gas cap seal 2. fuel vent valve (97+) 3. EVAP canister behind fron bumper passenger vent.

1999 Eclipse GS
Built motor
Hahn 16G Turbo w/ FMIC
Hahn Stage 5 Portfueler (270's & 500's)
Zeitronix Zt-2 wideband w/ 3.5bar MAP
3" SS Turbo Back
CM Stage 4 Clutch and Fidanza Flywheel
Baer Big Brake Kit

Thanks for the info on the exhaust leaks. If this is truly possible, it could very well be that. I mentioned that i have a test pipe res. in place of the cat, could low back pressure be the cause? Wouldn't think so with the magnaflow muffler, its not a straight through design. However, I will check the exhaust gaskets, they may be leaking.

Regarding the o2, I changed it and code went away. I'm not totally convinced that its giving accurate readings, but at $60 bucks a pop I don't wanna buy another.

Also just changed plugs and wires, did not make a difference, so i put the old ones back in. Plugs showed evidence of lean condition. They where hot white.

no exhaust leaks. I checked all the gaskets including manifold. No holes in the pipe. its brand new......

Anyone got anymore ideas to throw at me?

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2012 2500HD LML

I'm not sure how or if i can. I did check fuel pressure its right where it needs to be.

Well figured out my problem today. It was my IAC after all. Put a brand new one in and it solved everything.

Thanks for all your help.