Hey all,

Recently did a bunch of upgrades to my Evo8 (2003, 67k miles) and I am experiencing a weird high idle issue. As soon as I start the car the idle jumps to about 2-2500 rpm and then after about 30 seconds, it goes to 4k rpm and sits there.

Not sure if the car just needs to get tuned now, which I am doing in 2 weeks, or I have a boost leak/mechanical failure.


Here are the upgrades I just did:

-Walbro 400 fuel pump

-FIC 1200 high-z injectors (resistor cut and crimped)

-AMS fuel rail

-Fuelab FPR

-Skunk2 intake manifold w/ thermal gasket

-S90 Billet TB w/ thermal gasket

-GSC S2 cams w/ Ti retainers and new valve stems

-Gates Blue Timing Belt w/ the usual upgrades you do during a timing belt change (pulleys, water pump etc)

-Grimmspeed 3 port EBC (port 2 goes to wastegate, port 3 to turbo outlet, port 3 not used and not sure if I should put a cap on it)

-ETS short route IC piping

-ETS 3.5” intercooler

-ETS 3” intake (speed density setup but currently have the stock MAF hooked up so I can start the car and get it on a trailer in 2 weeks)

-HKS SQV

-Radium Engineering dual catch can kit


Still on stock Evo8 turbo until I upgrade later.

No matter what I change: fuel pressure, adjust TPS,
BISS etc. No real change in idle. EGR system has been removed and currently venting EVAP to air. Double checked my timing and all timing marks line up.

Quick note on the Skunk2 intake manifold:

-HKS SQV has a dedicated vacuum port to intake manifold

-FPR has dedicated vacuum port to intake manifold

-Defi boost gauge has dedicated vacuum port to intake manifold

-Passenger side Radium catch can goes from back of valve cover and then to dedicated vacuum port on the intake manifold

-Brake booster has dedicated vacuum port to intake manifold

Not sure if I am overthinking things and it’s a “the car needs a tune” or it’s a boost leak situation or a sensor failure. Thinking is that the idle should still be normal due to the base map. Car was tuned about 2yrs ago by KC Tuned in Charlotte, NC on stock fuel pump and injectors (basically everything was stock except a 3” downpipe and 3” exhaust during the tune).

In the next few days I will do a boost leak test to make sure I am not having an air leak issue.

I looked through multiple threads and did not find exactly my situation.

Any input is appreciated and apologies for the long first post.

 

I am not sure what it is maybe someone else will chime in but if you did all of those at one time and it hasn't been tuned yet, i would definitely say its the tune. Have the tuner send you a base map after you have sent him a list of all the changes, thats what i would do.

 

Thanks. I would agree. Going to do a boost leak test sometime this week just to be sure that I don’t have any leaks anywhere. If boost leak looks all good then I can only think that it would be the tune.

I was hoping, since it was previously tuned on stock injectors etc, that the previous tune would help me out so I can at least set the fuel pressure to correct PSI and adjust the TPS properly.

 

No with new Injectors and pump definitely need a tune.

 

Gotcha. I am clueless when it comes to tuning but it makes sense that it would definitely need it after all the changes.

 

Have you looked at your S90 TB and the biss/Idle screw that's on it?
Also slapping on new injectors without dialing them in would cause serious idle issues.

 

I did. Unscrewing the BISS caused the issue to worsen. It seemed that way at least. I screwed it all the way in and it helped a bit. It definitely felt like the ECU was compensating for something and raising the rpm to dump more fuel in the car. I did find a few boost leaks after doing a boost leak test. PCV connection to the intake manifold and PCV back of valve cover was leaking air bad. So I have fixed that with a different clamp.

I figured it would cause idling issues but wasn’t sure if it was going to be this bad. I wanted to confirm if it made sense that it jumps up to 4k rpm.

Thanks for the reply and help.

 

If you went from stock injectors to 1200 without tune, then that would definitely cause a serious idle issue.
Basically your injectors scaling in the ecu would be saying you have 660cc injectors when it reality you have 1200cc ... So it would definitely dump a **** load of fuel.
I am not sure how you expect your car to idle properly after changing the injectors and not tuning for it.

 

Thanks. I definitely wasn’t expecting it to idle like normal. I just wasn’t sure if it’s going to jump up that high. I appreciate the input.

 

those would be considered fairly major changes to the fuel system = tune

 

Thanks. I’ll throw the old injectors on so I can at least set the FPR/TPS so it will be ready for the tune next week.

 

Did you fix the high idle? You have a major vacuum leak somewhere starting from the throtel body going towards the intake manifold. With that kind of RPM you should be able to hear the hissing sound from the vacuum leak. Re-installing the stock injectors will not solve your problem. GL

 

Yeah, I fixed it. Ended up being that the throttle body was way open and TPS had to be adjusted. Once I adjusted the throttle body and TPS, then the idle went down to normal. Even with the 1200cc injectors and Walbro 400.

Got it tuned over the weekend. Made 377hp/369tq.

 

I had a feeling it was the S90 TB ... Going from the stock to an aftermarket TB always requires an adjustment to get things dialed in.

Although at your power levels, I would've kept the stock TB. I would've just done the shaft seals. Driveability on the stock TB is smoother.

Even at 700hp my car was considerably smoother with the stock tb. I am running a fullblown and it is sensitive in low rpms. S3 cams and 2150cc injectors definitely dont help either.

 

I completely forgot that I messed with the S90 TB before I even installed it.

I agree about not really needing the TB at my power levels. Figured since I was doing the Intake Manifold, might as well do the TB. Plus, I am always planning for the future with this build. Once you reach a certain power level, you always want to go higher.

Hopefully in a few months I’ll be upgrading the turbo.