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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 6967
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Lancer Oz Rally: I have a 2004 Lancer Oz rally edition.

Customer Question

I have a 2004 Lancer Oz rally edition. I have been having a problem with the car stuttering at idle with the A/C on. Car runs great on the freeway with the A/C off or on. I have replaced plugs and the wires look good. Cleaned IAC, throttle body, mass air flow and have a new air filter. Not sure if this is related but my cruise control just went out, no light on and my cluster fuse just blew the other day. Let me know what test you have.
Submitted: 2 years ago.
Category: Mitsubishi
Expert:  Doug replied 2 years ago.

Start the engine and let it warm up to idle. Then turn the AC on while watching the tachometer. Does the tach go up slightly when you turn it on (then likely back down), or does it go down when the compressor engages without going up first?
Customer: replied 2 years ago.

At warm up idle rpms are around 700, I turn the ac on and it goes to around 860 and whenthe compressor disengages it goes back down around 720 or so.

Expert:  Doug replied 2 years ago.
Thanks... so the idle up is working properly, that is good.

How bad of a stutter are we talking about here? Is it bad like a misfire or just lacking in power? If the latter... how recent is this condition?
Customer: replied 2 years ago.

The stutter only occurs bad when at a stop light with the ac on. The car jerks a little and the rpms go down under 500 and then back up to 800 or so. Feels like the car is going to die then it revs itself back up. I have noticed at night time when it does it you can see the interior lights flicker when it starts to stutter. When taking off from a stop light the car kinda jerks and then starts to go, but soon as you get going the power is there. Just started noticing it the past couple months since the ac had to be turned. No problems with heater or regular air.

Expert:  Doug replied 2 years ago.

Is there any abnormality recently with the AC at all? Any indication that the compressor may be dragging (less efficient AC, "new" hum or similar noise from compressor, etc)?
Customer: replied 2 years ago.

No ac works perfect and blows very cold air. I cant hear any noises coming from the compressor.

Expert:  Doug replied 2 years ago.
Hmm, that really is a pretty odd one. I feel the load from the ac compressor is likely your primary concern, it doesn't sound like the engine itself is an issue.
No one has fooled with the throttle stops or air bypass screw right?
Customer: replied 2 years ago.

No adjustments on the the throttle body at all. Any way to check load on the compressor?

Expert:  Doug replied 2 years ago.
Thanks. Unfortunately there isn't any real accurate way to measure the load, which is why we would be looking for abnormal behavior from the compressor as a sign of issue.
Could we check to see the operating voltage with a.c. on versus off?
Customer: replied 2 years ago.

Yeah, steps to do that

Expert:  Doug replied 2 years ago.
We just need a DC volt meter, hooked up between the positive and negative battery terminals to get a reading at idle, then another reading with the compressor engaged. If you could get me the RPM at the time as well that would be great.
Customer: replied 2 years ago.

Ok got a few numbers for you. These numbers are with ac on and off sitting at warm idle, all accessories off.


Calculated Load - 17.3% 26.3%

MAF 0.27 Lb/m 0.53

MAP 8.0 Hg 11.2 IAT 131 deg 129

IGN ADV 7.0 10.0

Voltage 14.14 14.08

RPM 715 832

Expert:  Doug replied 2 years ago.
Hmm, really nothing unusual there at all. The only thing that is noteworthy is the idle is just slightly on the low side (100 RPM or so tops).
Does your scan tool have actuator tests? To the point, do you have something that says SAS or Base Idle?
Customer: replied 2 years ago.

No its not that I depth

Expert:  Doug replied 2 years ago.

Really the only thing I can see would be if somehow the air bypass got out of spec, but that is pretty unusual to happen without any influence.

Lets just do a quick increase of the bypass and see how it responds. Look on the top of the throttle body and you should see a ~3/8" bore hole on the top near the firewall side with a screw inside it. Take a screw driver and turn the screw a half turn in and then drive it and compare behavior. If you see some improvement and want to try a small amount more you can... but keep track of how much you adjust so it can be undone later.
Customer: replied 2 years ago.

I turned that screw half turn in and drove it today, still no change. I did a live data stream while driving. In Park the car idles at 860-880 with the ac on and when i put it in drive it goes down around 698-710 and when im at a stop light it sits around 710 then down to around 500 when it feels like it is going to die.

Expert:  Doug replied 2 years ago.

And you are seeing adequate idle increase before the compressor engages right?

Is there any possibility that the timing belt may have been replaced recently and is perhaps too tight or off a tooth?
Customer: replied 2 years ago.

I wasn't listening for the compressor but will do another drive and let you know.

I have had the car for a couple years and I haven't touched the timing belt at all, the car does have 160k on it, so not sure if timing has ever been done.

Expert:  Doug replied 2 years ago.

Lets get a drive and see if you are definitely seeing it idle up or not.

I'd rather not delve into the timing belt for this as it is such a long shot... but I'm honestly running out of ideas.
The timing belt does need to be addressed though if you don't know the history... they are 60k belts and they will destroy the engine if they break/slip.