ISR Mod: Cheap Power Gains, or Fake News?

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The Toyota ISR mod is one of the oldest tricks in the book. But does it help or hurt your cause?

If there’s one thing you can bank on in life, it’s the ingenuity of automotive enthusiasts. Hot rodding began shortly after the introduction of the automobile, and people have been working to make their vehicles better ever since. Oftentimes, this means buying expensive go-fast goodies. But there are ways to make your truck sound or perform better on the cheap. But sometimes, as is the case with the Toyota ISR mod, the benefits are questionable.

The pros and cons of the ISR mod have been debated for years. And there are plenty of Yota Tech threads addressing the matter. But tbst1337 was looking for some clarity on the issue, so he headed over and started a new thread seeking advice.

“I know there are a lot of ISR mod threads out there, and I’ve read a lot of them. Most things are clear to me, but in the pictures I see, there is no sign of an EGR box anywhere to be found anymore (marked in red in the picture hereafter).

Now I see that there are two lines going into it, and one line + 1 ‘pipe’ coming out. If I were to do the ISR mod now, I would have one pipe. Thinking about an aluminum spectre intake since I don’t have too many tools yet. Going from the air box to the intake with two vacuum lines attached. But then there is no connection to the pipe coming out of the EGR box anymore. Is that how it should be?”


Almost immediately, Mclaws89 chimes in with a little clarification.

“Most of the ones I am familiar with eliminate the two black boxes bolted to the airbox with 10mm bolts. The hoses they used to connect to on the intake plenum are just plugged. You will need to do something about the hose going from the valve cover to the intake hose. I have seen little aftermarket filters on there or you can easily splice a hose into the new intake. But yeah, those two boxes you circled you can just unbolt and put on the shelf in the garage.”

Of course, whether the ISR mod actually does anything worthwhile for your truck is up for debate.

“Do you like doing mods to your truck that serve no useful purpose???” asks millball.

“The mod really doesn’t help performance at all,” adds Mclaws89.“Decreases the longevity of the intake and makes stuff louder. If you do the project, hold onto the original stuff. If you are anything like me you will want to throw it back in in ten years. When you are sick of looking at the aftermarket one in there. But projects like this are fun and everyone should try stuff on their truck.”

Even so, there’s at least one benefit to doing so, according to maninnepa.

“Getting rid of those two boxes and hoses makes it a LOT easier to check your tranny fluid if you have an automatic!”


All jokes aside, the OP has, like us, seen cases elsewhere where the ISR mod resulted in some tangible benefits.

“From what I was reading it seems to

  • Increase lower rpm torque a bit (questionable, even though I have looked the dyno tests).
  • Makes it sound a bit throatier.
  • Will result in higher mpgs.

Currently, I am a little underwhelmed by the sound this car makes. Hoping for just a tiny bit more of a hot rod/American truck sound out of it. Thought this cheap mod might achieve that.”

As Mclaws89 notes, an exhaust upgrade is a much better bet to achieve those desired results, however.

“The exhaust is easily the better mod. A high-flow cat and muffler on a 2 1/4 pipe is good for the engine breathing and the sound. You can try the intake mod. It really won’t hurt anything. I doubt you will find that it increases your sound quality much though.”

Toyota 4Runner

Regardless, Kolton5543 chimes in with useful tips in case the OP wants to go through with the ISR mod.

“It’s an easy mod to do. The boxes are there for nothing more than to silence intake noise. I replaced mine with a single pipe and a cone filter. I did it strictly to free up space in the engine bay. The intake is only a tad louder but not annoying. It actually has a pretty good note I think.

As for the hoses, they are important and can’t just have a mini filter installed. They all will essentially introduce a vacuum leak and cause a lean condition if they aren’t plumbed into the intake piping after the AFM. The one on the valve cover is the PCV vent and is absolutely required. The small one out front is for the A/C and power steering idle up control. If you have neither of these functioning, feel free to cap them off or leave them disconnected. The large one is for the PAIR valve. Again, if it’s non-functional or deleted you can cap it off.

EDIT: The pair valve doesn’t actually need to be plumbed after the AFM. If done so it’ll actually cause a rich condition. It only needs to be filtered, so plumb it in between the AFM and the filter, or give it its own filter.

Also it’s the noisiest among them. That’s why it got its own silencer from the factory. If you only filter it, you will definitely hear some extra noise, mainly at idle. Ultimately I’d recommend just deleting it along with the EGR as long as you’re not tied down by the EPA. It was worthwhile for me. It makes for fewer components to fail and makes changing spark plugs about a 5 minute task.”

All of which is excellent information if you’re interested in trying out the ISR mod on your Toyota pickup. But we’re curious to know – what is your opinion on the mod itself? Is it a waste of time and potential danger to your truck? Or is it a worthwhile, inexpensive way to get more power and/or better sound from your engine? Head over here and chime in with your thoughts!

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Brett Foote has been covering the automotive industry for over five years and is a longtime contributor to Internet Brands’ Auto Group sites, including Chevrolet Forum, Rennlist, and Ford Truck Enthusiasts, among other popular sites.

He has been an automotive enthusiast since the day he came into this world and rode home from the hospital in a first-gen Mustang, and he's been wrenching on them nearly as long.

In addition to his expertise writing about cars, trucks, motorcycles, and every other type of automobile, Brett had spent several years running parts for local auto dealerships.

You can follow along with his builds and various automotive shenanigans on Instagram: @bfoote.

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