Finally figured out what caused my idle surge issue and rough idle on my 2003 Lancer Evolution

[@CO_EVO_8]

I've been dealing with idle issues since I bought my Evo 8. 03 as well. The car will either cold start correctly or it won't. If you give it load then neutral the car it dies. The car almost dies then catches itself coming to lights. Ive had several people look at it and can't figure the issue out. I haven't been able to enjoy the car since I bought it almost 2 years ago due to this issue. I'm going to check this out and see if mine may be the same. I'm ready to launch this car off a cliff at this point with the amount of money I've spent trying to dial the idle. Rebuilt the entire throttle body, multiple tuning sessions, boost leak tests, etc. Makes me miss my Evo X. Never had any issues with the car, ever lol

[@itsnevo8757]

@@CO_EVO_8 I feel your pain! Also check the hose that goes from the intake through the firewall and to your boost gauge. Mine was dried up and split on one end so as soon as I fixed that, it seemed to help on my car.

[@jhonreydelacruz6945]

My evo surges when I use the AC. when I come to a stop, it will rev up and down. Any thhoughts? It only happens when I use the ac

[@itsnevo8757]

@@jhonreydelacruz6945 that’s a good question…I’d think if it was something like a throttle position sensor or a vacuum leak it would act up even when the AC is not on but that’s strange it only happens when the Ac is on. I’d check the AC refrigerant level and see if it’s really low because I think that can cause idle surge. You may have bad AC compressor as well.

[@zipone_1726]

Im having the same issue. I did a boost leak test tho.

[@itsnevo8757]

I discovered my boost gauge wasn’t reading vacuum at the range it should be at and I was able to track a leak in the rubber line running from the engine bay into the interior, it looks like it was a factory line that was capped so it would be easier to connect a boost gauge. That rubber hose was really dried out and had a split of about an inch where it mounted to the hard line in the engine bay on the passenger side by the firewall. Since fixing that issue I haven’t really noticed any new idle issues but I haven’t really been driving it much. I travel for my job so I haven’t been home all that much lately.

[@JakeReesman]

is the mileage correct?? that car is beautiful for 247k

[@itsnevo8757]

Thank you! Yep, the mileage is accurate. I know lots of people avoid high mileage cars but this one was very well kept and it’s rust free which is very rare these days no matter the mileage.

[@paulwilliams6534]

Has it been repainted? I noticed it has a shorter throttle cable because theres a mount missing on the front of valve cover@@itsnevo8757

[@itsnevo8757]

@@paulwilliams6534the only panel that has been repainted has been the front bumper. The rear bumper still has some scratches that were reported on Carfax back in 2019. There are scratches all over the body but it all appears to be original paint. That could be the case. I noticed there was something that once looked like it was mounted to the valve cover on the front but didn’t see anything that looked like it mounted there and the cable does seem to be a bit too tightly stretched so maybe someone replaced the cable with the wrong length

[@paulwilliams6534]

@@itsnevo8757 oh nice. Yeah looks like it, I didnt like the stretched angle of it coming from. Firewall but if it doesn't cause any issues keep it on there. Original cable is a bit longer to make the larger sweeping curve

[@itsnevo8757]

@@paulwilliams6534it seemed like that throttle cable was always too tight so maybe I’ll order the correct cable and see if that helps

[@mike_0213]

I have an idle issue in a 2013 Lancer ES - In park it is not too bad but the idle is still going up and down. When I put the car in drive and say I am stopped at a light the idle goes up and down like 500-600RPM and the car wants to jump forward. I know I do not have an EVO but do you think a vacuum leak can cause this too? Or is there something easier to do first?

[@itsnevo8757]

@@mike_0213 when you have vacuum leaks it definitely can cause issues with your idle but there are a few sensors that can also mess with your idle as well. If you want to check if you have a vacuum leak, just start spraying something like water from a spray bottle onto any vacuum lines and the moment you spray it onto a vacuum leak the idle should stop surging. Just take your time spraying so you can identify where specifically the leak is coming from. You should also be able to head an audible hissing noise if you have a vacuum leak. You can start to feel around each vacuum line if you hear a hissing sound and the moment your fingers cover the vacuum leak, the idle should become normal. The Idle air control valve (IACV) could be bad on your car as well. I’ve purchased several for my Evo and had the idle act differently with each IACV I installed. At least for the Evo, it sounds like it’s a common part to go bad and it sounds like many people have replaced them and instantly had no more idle problems. The problem is the price can vary from $20 to $350 or more and I’ve heard several people say don’t buy a cheap one because it’s hit or miss if it even works and could act up quickly after installing. I was always told buy direct from the dealership to have the best chance but those are pricy, especially if it’s not the cause of your issue. The throttle position sensor and the cam sensor are also some of the sensors that can cause an issue with idle surge as well.

[@mike_0213]

@@itsnevo8757 Thank you for the reply. Do you know if these two issues would throw codes? (throttle position sensor and the cam sensor)

[@itsnevo8757]

@@mike_0213 I know on my Evo I didn’t always have a code when the idle was all over the place but I think with my Evo it was a combination of a vacuum leak and bad sensors