Subaru Standalone ECU vs TGV/Air Pump Replacement

Disclaimer

We, at JM, always suggest sticking with the stock ECU over a standalone EMS unless your car is a 100% dedicated race car and you need the additional features that the Cobb Accessport cannot support. Between the possibility of future emissions testing, drivability differences, vehicle resale value, and being more user friendly. Basically if you have any emissions related deletes we suggest spending the time, money, and energy on reinstalling those parts.

Why the Stock ECU is better than a aftermarket ECU for street driven vehicles

The resale value of a car with an aftermarket ECU and/or extreme mods is typically way lower than a stock car or light modifications. No dealership is going to take it as a trade in and most people shopping for these types of cars are also purchasing these cars at dealerships. Even if they are not purchasing from a dealership, most people are looking for stock or close to stock vehicles, not something with a bunch of emissions parts deleted. Cars with extreme mods usually take a very long time to sell, a standalone EMS would be considered an extreme mod.

The Cobb Accessport with the factory ECU has many many features. It is extremely rare that a Standalone EMS is going to benefit you in any way on a street driven vehicle. The Cobb Accessport can do basically anything you need and many of the fastest Subaru’s in the world still use the Cobb Accessport. The Accessport has many user friendly features associated with the handheld device and tuning that is very hard to match with even a Standalone EMS.

I’m sure Cobb is hard at work on a new version of flex fuel. Flex fuel was one of the most popular Cobb products we sold. I cant imagine they wont figure out a new way to implement it.

Maintaining Emission Compliance While Modifying Your Car

We have had a lot of inquiries on what can be done if you have your Air Pump, EGR, TGV, Rear O2, or any Evap deleted on your Subaru WRX or STI. A lot of customers have been asking to just leave them deleted and go standalone ECU. Below we have the cost of purchasing all of the components, if you don’t have any, vs getting a standalone ECU. For street-driven vehicles, you will need to re-install those components. The information below is mostly suited for track only cars, but it also helps street driven vehicle owners with prices for the emissions components.

Unfortunately leaving them uninstalled and just dealing with the check engine light is not going to work. In our testing, we have found that having any of the TGV, Air Pump, or EGR codes can cause the boost control to not work or to always have -4.92 feedback knock reported at all engine conditions except idle. That’s not going to work very well when you need boost or proper ignition timing for your car to run correctly. You also wont pass any emissions test if your state has them with a check engine light on.

Cost to replace Air Pump and TGV’s

Pricing is going to vary depending on what you all have deleted and if you have any of the original parts. Below I have a price breakdown for the worst-case scenario of not having any of the parts. Some of these parts are no longer available brand new so you may have to source some used parts from junk yards. We have found some parts can have long lead time to get as well.

(These prices are parts only; labor is going to be extra and will vary depending on what parts you do and don’t have and whether you install the parts yourself or pay a shop to do that.)

2002-2003 WRX

The Passenger side TGV is no longer available, used intake manifolds are going for under $200 from our local junkyard

2004-2005 WRX

Both TGV’s and needed gaskets – $ 830.00

2006-2007 WRX

Both TGV’s and needed gaskets – $830.00
All Air Pump components $2,200.00-2,280.00

2008-2014 WRX

Both TGV’s and needed gaskets – $815.00
All Air Pump components including pump, valves, hoses, gaskets, and hardware – $2,000.00

2015-2021 WRX

Both TGV’s and needed gaskets – $775.00
All EGR Components including EGR Valve, Cooler, EGR Pipe, Gaskets, and Hardware – $600.00

2004-2006 STI

Both TGV’s and needed gaskets – $920.00

2007 STI

Both TGV’s and needed gaskets – $830.00
All Air Pump Components – $1,600.00+
- Engine Air Resonator is no longer available, this is basically a block off as the passenger head has a block off plate installed from the factory.

2008-2021 STI

Both TGV’s and needed gaskets – $830.00
All Air Pump components including pump, valves, hoses, gaskets, and hardware – $2,230.00

Things to consider before purchasing an aftermarket ECU

With the price breakdown, we can see that if you need to replace everything you will be looking at $800.00-3,000.00 depending on your year and what parts you all have. We have a lot of people inquiring about just leaving all the parts deleted and going aftermarket ECU. Ultimately you have a few things to consider if you are wanting to ditch the factory ECU in favor of an aftermarket ECU.

Local Laws – Do you live in a state that requires emission testing in order to keep it registered? If you do you will never pass those tests with a standalone ECU.
Aftermarket ECU support for your vehicle – There is a plethora of options for aftermarket ECU’s for the STI and WRX. The big question is if the ECU fully supports your car. 2008 and new WRX and STI have CANbus systems. CANbus requires special codding from the ECU manufacturer to keep all the other components like ABS, Traction Control, Cruise Control, Radio, Si Drive, and DCCD happy and communicating together properly. 2015+ WRX are direct injected and there are only a few aftermarket ECU’s that have support for both direct injection and Subaru’s CAN system.
Cost – I will break down the cost below, but that is an important thing to consider. There is a lot more to factor in than just the cost of the ECU itself. While most of the ECU manufacturers have base tunes that will run a stock car, you are going to need a tune if you install an aftermarket ECU. Tunes for aftermarket ECU’s typically cost more than when tuning on the stock Subaru ECU as well.
Drivability – The OEM ECU is built to run one engine and the OEM spends thousands of hours to get that engine running well in almost any condition imaginable. I personally have spent many hours sitting in Subaru’s while it is -20f outside working on the cold starts when running E85. That knowledge may not transfer over directly from the OEM ECU to an Aftermarket ECU because the tables for starting and warm up are different. That’s not to say you can’t get them running well. It just takes a tuner that has a lot of experience with a particular ECU and has taken the time to get that testing done. Most of that testing can’t be accomplished in the few hours that your tuner gets with your car on the dyno.
Tuner Support – Before you go and buy a ECU make sure your tuner of choice is familiar with that ECU. It is best to talk to your tuner about what ECU’s they like are are comfortable with and purchase it through them.

What ECU is right for me

With so many aftermarket ECU’s it can be overwhelming picking one. The OEM ECU is what we will always recommend to our customers who drive their cars on the streets. You can get your stock ECU tuned in several different ways. Cobb, Opensource, and EcuTek all have support for tuning your stock ECU and they are proven to work well. Tuning with the stock ECU you are much more likely to be able to pass any emission test your state does. With Cobb’s new greenspeed we have cars making 500+ hp with the TGV/Air Pumps installed and GESi catalytic converters. Being emmisions compliant is not going to drop your power by much if any.

Cobb has a lot of products that are 50 state legal with California Air Resources Board (CARB) Executive Order (EO) numbers. These CARB EO parts paired with a proper tune can help you pass an emission test. An aftermarket ECU is never going to pass an emission test as it won’t communicate with the tester that they plug into the obd2 port. Aftermarket ECU’s are only recommended if you track your car and don’t drive it on the streets.

Another thing to consider is the available inputs on the ECU you choose. Inputs are any sensors that send data to the ECU. Examples would be Coolant / Intake Air Temp, Front O2, Rear O2, Crank / Cam Sensors, MAF / MAP Sensors. The ECU’s listed below all have enough extra inputs to run flex fuel, fuel pressure, and wideband for closed loop fuel control. Most of them also have available inputs to do add oil pressure / temp. Five extra ECU inputs may sound like a lot but that’s actually how many inputs we used to have when tuning with Cobb in the pre green era. My personal 2006 WRX on a pre greenspeed tune could log Wideband AFR, Ethanol Content, Fuel Pressure, Oil Pressure, and Oil Temp all on the OEM ECU.

Current features available for 2008-2021 WRX and STI with Cobb Accessport as of 12-7-2022:

You might be wondering what features are still available when tuning with a Cobb Accessport. Below is a breakdown of some of Cobbs Custom Features that you can still use. The Cobb Accessport is still the most popular tuning option at our shop and likely at most other shops as well.

Running Ethanol – Yes, even though flex fuel is not currently available, you can still run E85 in your car. Flex fuel was never a requirement to run ethanol. It made running extremely E85 user friendly, but running E85 is not dependent on flex fuel to be tuned.
Storing multiple tunes on the Accessport – Installing a ethanol gauge and having multiple tunes you can flash the correct tune for current ethanol in the fuel tank. You can even flash the tune with the car running and it takes only moments to flash when re fueling. Basically a poor mans flex fuel.
Speed Density
Launch Control
Per Gear Boost / Wastegate Duty Targets
Launch Control
Flat Foot Shift

Below is a breakdown of different ECU’s for specific years and models

2002-2005 WRX

2006-2007 WRX

2008-2014 WRX

2015-2021 WRX

2004-2007 STI

2008-2014 STI

2015-2021 STI

2002-2005 WRX

Stock ECU

The stock ECU from the 2002-2003 WRX can run the Carbarry ROM. This ROM has all the features a typical enthusiast needs like, flex fuel / dual maps, speed density, launch control, and flat foot shift. I have tuned many rally cars this way and it works extremely well.

-The cost of this ECU can be $0 if you have a 2002-2003 WRX or a used ECU can be picked up for a few hundred dollars.

AEM Infinity 506

Minimum needed to get running
- ECU Cost – 1,506.92
- Plug and Play Harness – $695 and up
- Wideband sensor wired directly to ECU or a gauge like AEM or Innovate can be used – $190 and up
- AEM Intake Air Temp Sensor (IAT) – $62
Optional Extras
- If you want Flex Fuel you can wire a sensor directly to the ECU or a gauge like Innovate can be used – $115 and up

Total for ECU NOT including a tune or install. Budget for at least another $1000 on top of this price – $2,453.92

Haltech Elite 2500

Minimum needed to get running
- ECU Cost – $2,090.00
- Plug and Play Harness – $579 and up
- Haltech CAN Wideband O2 Controller – $329.00
- AEM Intake Air Temp Sensor (IAT) – $62
Optional Extras
- If you want Flex Fuel you can wire a sensor directly to the ECU or a gauge like Innovate can be used – $115 and up
- Haltech CAN Expander box may be needed depending on available inputs for flex or additional sensors – $481.00

Total for ECU NOT including a tune or install. Budget for at least another $1000 on top of this price – $3,060.00

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