DIY - Vacuum Leak Detection - Toyota Nation Forum : Toyota Car and Truck Forums
Corolla 7th Generation (1993-1997) Specific discussion of the 7th generation

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post #1 of 8 Old 05-14-2019, 10:57 PM Thread Starter
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DIY - Vacuum Leak Detection

Vacuum leaks are primary cause of lean-condition error codes. On MAP cars, vacuum leaks don't cause as much driveability issues as with MAF-sensing. However, it still results in stumbling, roller-coaster idle, poor throttle-response and loss of power. Many people suggest propane, carb-cleaner, water or smoke squirting to find leaks. But this is iffy method requiring lots of previous experience and skill in listening to idle tone. Also not as helpful when you've got multiple leaks.

I prefer pressure-test with soapy water as bubbles will appear on outside of engine instead of inside like other methods. I wrote up procedure with photos here: Dreaded P0171 Lean Condition. This vacuum-leak test works on any car, regardless of MAP or MAF sensing and gives 100% confirmation and location of leaks regardless of the user's skill and experience level. This test has found multiple leaks numerous times where other methods have failed.
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post #2 of 8 Old 05-14-2019, 10:59 PM Thread Starter
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heck, I'll just repost it here.

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Originally Posted by DannoXYZ View Post
All this reliance on electronics makes people soft and not capable of critcal thinking and logic. They just want answers and be told what to do. When apocalypse comes, those who can't set traps for rabbit or kill with your bare hands are gonna starve to death! Zombies are gonna getcha even though they're slower than molasses! Come see our newest game in Orlando: http://nomadicvr.com

Now, i'm going to show you some survival skillz. Put down the xbox, or tablet or whatever gizmo is your temple of Truth and get hands-on dirty and touch your car physically and mechanically. Touch it, feel it vibrate, learn how it sounds when it's healthy and when it's sick. Pull and yank on hoses to see if idle note changes. Squirting with propane, carb-cleaner, water or even strategic aiming of pee can help, but you need to have some prior experience to recognize the subtle change in idle tone. And you need to know where to squirt.

Here's a sure-fire 100% way to find vacuum leaks with positive visual confirmation.

1. Plug your exhaust with banana, potatoe, cork, wet-rag or whatever gives 100% blockage

2. Make a plug fitting that replaces MAF on intake hose with compressor quick-fitting


3. Install your plug into intake hose which normally connects to outlet of MAF


4. Then set compressor to 3-5psi and connect to fitting

5. Squirt soapy water at every connection point from intake hose all the way to intake valves. Every seam, every joint, every clamp, etc. Pay particular attention to intake-manifold to head mating surface. Also injector tips.

In this case ironically, I had leak at external idle-valve. There's O-rings and seal inside case of idle-valve that needs replacing.


And another leak at throttle-body/TPS. There's O-rings on both sides of butterfly shaft that needs refreshing.


Also leak by dipstick tube. Looks like someone previously replaced O-ring with one that's too big. New correct O-ring with some sealant takes care of that!


Bubbles stay around leaks and gives you time to find them. Squirting propane isn't nearly as effective because you need to squirt at ALL leaks simultaneously for enough to get into engine to affect idle note. And you can't see propane and see exactly where it was sucked in. Bubbles are easier!!!
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post #3 of 8 Old 05-15-2019, 12:20 AM
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Where do you recommend aiming the pee-stream?
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post #4 of 8 Old 05-15-2019, 05:38 PM Thread Starter
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post #5 of 8 Old 05-16-2019, 08:45 AM
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@Haloruler64 - add to DIY thread?
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post #6 of 8 Old 05-17-2019, 11:38 AM
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Where do you recommend aiming the pee-stream?
Ask a newer diesel!

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post #7 of 8 Old 05-17-2019, 09:16 PM
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Ask a newer diesel!
Funny how you never see blue on those urine colour/dehydration charts...

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post #8 of 8 Old 05-18-2019, 04:18 AM
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@Haloruler64 - add to DIY thread?
Good call!
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