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Discussion Starter #1
Hey ya'll. Long story short, my MR's bogging at lights/idle. Seemed to be running fine for a while but out of no where it began bogging down when stopped as well as threw an P0300 code. I've tried a few things, checked all my vacuum lines, made sure intercooler piping is tight, replaced sparks with a new set of NGK's, tested the coil packs (They passed, but just barely. and I mean barely.), ran injector cleaner through the fuel tank, and replaced the fuel pump relay with the orange one. The light's/code's gone away but the motor still bogs and it worries me. It wil move around from 1200-500 rpm, typically hanging out at 1000, but it randomly bog and then pick up to 1200 so it doesnt die. Before it hung out around 1000-750, and I was fine with that, but this doesnt feel right.

Car is bone stock besides for a cold air intake btw. And other than at lights the engine runs fine, pulls like a monster, just doesnt like hanging out at idle.
 

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Discussion Starter #2
Help? Anyone? I'd like to try to solve this today as it's really my only time off to work on the car.
 

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I have that issue when the air conditioning is on. I turn the a/c off and idle is good. My 2 cents. Hope you get it sorted out.
 

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dirty throttle body

I had a similar issues on my GSR. Turned out to be a dirty throttle body plate. Cleaned it up and haven't had the issue since.
 

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Discussion Starter #5
I have that issue when the air conditioning is on. I turn the a/c off and idle is good. My 2 cents. Hope you get it sorted out.
Sadly it's not that, I'm up in colorado so now I'm using the heater. part of the reason it's scaring me. It's gotten better the last few days, but it's still worrying
 

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Discussion Starter #6
I had a similar issues on my GSR. Turned out to be a dirty throttle body plate. Cleaned it up and haven't had the issue since.
I'm 110% checking that tomorrow. The car is a 105k miles into its life, god knows it probably needs to be cleaned just for maintenance sake. Dont 100% see how that could be the cause of the issue, BUT I'm willing to try/check anything for my pride and joys health lol. Thank you for your recommendation, I truly appreciate it. :D
 

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The intake is your issue. If the car is tuned, you need to check with your tuner about your target idle. I had a similar issue that I was battling to figure out. Although my car would stall after coming to a full stop and trying to take off on light throttle.
 

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What intake do you have? Because if the fans cut on, they can blow hot air in the intake and the extra air makes the engine stumble.

The A/C will technically still be on, or act like it is on even if the heat is on. So that could still be your issue.
 

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Discussion Starter #9
Fixed!

So it's pretty much gone now, idle moves from around 100 to 800 and it does not sound like its misfiring anymore.

Here's what I did:
1: Replaced sparks
2: Tested coil packs
3: Ran 2 bottles of injector cleaner through the tank (Seafoams concentrated stuff) One right after the other.
4: Compression test (This was more for my own sanity and probably isnt needed at all)
5: Completely took apart intake, intercooler piping, intercooler, and intake manifold, BOV, Throttle body and cleaned everything until it looked new. (Took like 6 hours and a few bloody knuckles. Used CRC Stuff from autozone)
6: ran a Valve/turbo cleaner through intake (once again, CRC Stuff).
7: Replaced all of my easily accessible vacuum lines with new silicone ones. (Once again, probably not needed but was done as a sanity thing.)
8: Replaced OEM fuel pump relay with recommended orange one.

Idk which of these actually did the trick, but for anyone that seems to be having the same issues in the future this is what I did. Like I said before I do not thing it was the ac system as it wasnt bogging from engine load, although everyone that said something about it 110% has a point and I recommend you make sure it isnt that's affecting your idle. But in my case my car was throwing a random misfire (P0300) and was 1000% misfiring. I went through the forums and tried everything that was already recommended, but nothing seemed to work. Finally now it's completely gone away. Once again if anyone else is experiencing idle/misfire issues please try everything recommended by more experienced users before you do everything I did, as I'm still a noob with the EVO platform and there's much more experienced users out there.
 

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Glad to hear. Gives me a good place to start. Good job:clap:
 

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I'm 110% checking that tomorrow. The car is a 105k miles into its life, god knows it probably needs to be cleaned just for maintenance sake. Dont 100% see how that could be the cause of the issue, BUT I'm willing to try/check anything for my pride and joys health lol. Thank you for your recommendation, I truly appreciate it. :D


So our cars adjust the throttle plate at idle if it needs too - and when its dirty like that, the plate can get stuck and not open/close in minor adjustments when its supposed to.

This is what i heard when my tuner/shop explained it to me. I probably butcher the explanation. Lol

I did the same thing you did, change and replaced everything. nothing worked. then i cleaned the throttle body plate last and it solved the issue for me.
 
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