Charcoal Filter

14 March 2004

Credits goes to: -

Thanks to Mr. Wong (levin818) a forumer in and for telling me about the charcoal filter requiring a vacuum line to suck the fuel fumes from the fuel tank a long long time ago and showing me the location and items. 

However at that time, I do NOT have enough hands-on experience to discern between it against all the other mass vacuum lines. I did not manage to study on his original JDM Levin GT-Apex AE101 to be effectively.     

There has been confirmation from but it is still not clear enough. A practical view is required.

Thanks to Allan Francis my friend who owns a MR2 SW20 3S-GTE 1991 which just recently made a top overhaul because of aging and changed all the vacuum hoses to blue color nylon type. Which looks very sexy :)

Thanks to Zul (GT20v) a forumer in and for telling me where to get the exotic blue colour vacuum hoses and take me to the shop to buy it.

Thanks to Yoga (yolk) a forumer in and for letting me study his charcoal filter's vacuum routes with patient. If not the charcoal filter requiring a vacuum line to suck the fuel fumes from the fuel tank will not be able to confirm 1000000%.

Now I have one vacuum port, doing nothing. It used to go to the charcoal filter's entry, which is now confirmed to be wrong. What an idiot. More like the mechanic who installed it is an idiot. :) And there is one hole in the intake plenum. 

So I thought they should be connected. I remember when we first transplanted this engine, we connected it this way and the engine's idling would jump sky high to 2,000 rpm. We thought it was wrong hence stick it to the charcoal filter instead. It dropped to 1,300 rpm. That figures looks more correct than 2,000 hence it was adopted as correct and the blame put to other items or issue. Which we know now is wrong. Anyway....

It is now know that OEM ECU are highly intelligent and that it will self compensate to great lengths so this time I let it run at 2,000 rpm and very quickly after a few km drive it reduce to 1,600 rpm. I gave it another two weeks and it reduced to 1,000 rpm without air-cond and 9,00 rpm with air-cond. Very good. It looks correct but it is not, 

Thanks to Patrick (anzacs02) a forumer in and for kindly and patiently wait for me to look at his vacuum lines. 

This is the 1st time I could ever see anything clearly without confusion. Perhaps the last vacuum hoses DIY change has helped me unconsciously in recognising vacuum hoses which to which. It is funny that before this, all attempts to look and study at other 20v is not successful.

It is found that the extra vacuum port that I have is supposed to be connected to the power steering rack and pinion's vacuum idle up valve / compensator. And that a return vacuum line comes back and is connected into the intake plenum.

My power steering rack and pinion is from the 80s which does not have the vacuum idle up valve / compensator found on newer models like the AE101. Hence it is no wonder we could not figure out why there is a extra vacuum port and why there is a extra hole at the intake plenum.

Now that this is all cleared up, the vacuum port is no longer required hence it is blocked. The hole at the intake plenum is also not required and it is blocked also.

A tiny copper pipe was installed and connected to the fuel tank to deliver the fuel fume to the charcoal filter and finally let it be sucked into the engine.

All the vacuum lines are where it should be. 100% of 100% now.

Start car and get out of workshop. Problems sss s s ss  idle low at 5,00 rpm. Dies .....

Oh nevermind, must be the ECU compensated the previous vacuum routing method too much, way beyond the correct method and now that it is back to normal, everything is "relatively" out of tune.

Oh nevermind, piece of cake. Start the car again and limp to a parking spot. Shut down. Remove EFI fuse 10 seconds to erase old memories. Put back the fuse. And start the car.

1,100 rpm then 3 seconds later drops to 900 rpm and with the usual tone of idling. PERFECTO. It is done. 

All healthy EFI engine behaves like this. To know if the EFI system is correct or not. Erase old ECU memory and start the car. It should go above regular idling a little but comes back down with in seconds.

This behaviour has been observed on many 20v. All good transplant behaves like this. I finally got mind now. Can't believe ..... only after so long........

When air-cond is switched on, the idling drops to 700 rpm. This is not surprising as the air-cond idle up screw has been messed with countless of times and may be wrong. So re-adjust to new environment. 900 rpm done.


  1. Vacuum Lines for Toyota 4A-G 20v AFM 1993
  2. Vacuum Lines for Power Steering & ISC Valve
  3. Charcoal Filter
  4. 4 throttles' Vacuum from Toyota Corolla Levin AE101 4A-GE 20v
  5. Fishtank Spiltter Vacuum



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