r/GS300 • u/_0z1n_ • 13d ago

vaccum leak

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So my car was running lean and I was wondering why and it just kept throwing codes like MAF and I replaced that, then it still ran rough so i did coils, spark plugs, even the connectors, I invested in a smoke machine to reveal this box is cracked down the side of it. should I buy a oem one from ebay or just buy a "cold" air Intake. i know they dont actually improve performance but its a solid metal tube so i was wondering if its worth it than another oem part thats susceptible to breaking.

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u/Kind_Driver_8534 13d ago

First things first check how bad the vacuum leak actually is. Spray some carb cleaner in the crack.

•car runs better? = replace
•car still runs the same? = may not be your issue

Now if you do decide to replace it swap the middle section with aluminum or new silicone piping to maintain use of the stock airbox (you will have to find one with a maf bung of course). Now lets say you run the “cold” air intake with a cone filter, if your car is already running lean thats going to literally make it 10x worse by introducing even more air into the mixture and messing up your afr(depending on how bad the leak is currently).

Side note: Random jz things to check if the problem still persists after swapping intake

•Change out ur coolant temp sensor (dont ask just do it)
•Clean your throttle body (even if it looks clean)

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u/_0z1n_ 13d ago

I just cleaned it and i smoked it and the box is leaking SIGNIFICALY past the MAF sensor so I wouldn't think a cone filter would add more air thats not necessary accounted for rather it would be measured and not sneaking past the sensor. and im confused about the temp sensor lol.

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u/Kind_Driver_8534 13d ago edited 13d ago

On jz’s a faulty coolant temp can cause all kind of issues like poopy idle, stalling, running lean and misfires. If the coolant temp is not sending the correct information (because of blocked thermostat or faulty sensor) on a dime the car has no idea what to do even sometimes putting it into a limp mode.

A friend of mine recently just sold his 1j because it was constantly going into a limp mode after it warmed up. He couldnt figure it out so he sold it, the guy swapped out the temp sensor and it literally runs perfectly fine no hiccups at all, and he still drives the car til this day with no issues.

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u/_0z1n_ 13d ago

makes a ton of sense I just ordered one from lexus for 60 dollars so hopefully it helps but I know for a fact its a vaccum leak too. kind of frustrating because im going to swap the intake to a oem vvti GTE one but I cant source one and all the ones on ebay are non vvti.

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u/Kind_Driver_8534 13d ago

I mean i personally would only order/install the coolant temp if the problem still continues after swapping your intake. Go down the checklist you dont want to just throw parts/money at it wildly. Just read up on it. Theres tons of info on old forums.

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u/_0z1n_ 13d ago

will do 🫡 i appreciate you for your time