Throttle Body



Most of the Mitsubishi EFI engines, just like most fuel injected engines, have a problem in regards to oil and sludge build up at the throttle body.  This is caused from the breather tube in the induction pipe breathing oily vapour.  This will cause a restriction in the air flow through the throttle plate thus less air will get through at idle and the idle speed may drop.  In Magnas, both 4cyl and 6cyl this may cause a slightly rough idle.  In the initial stages you will not notice as the Idle Speed system should compensate.  As the car builds up mileage the problem will get worse as the internals wear and you get more blow by (this is when combustion gasses escape past the piston rings or past valve stem seals and build up pressure in the crankcase.)  So how to fix, read below........(this is based on a V6 Magna however most Mitsubishis will be similar)

What you will need:

I am a strong believer that when ever you remove a part that has a gasket it is wise to replace that gasket as it will not compress a second time thus you may not get a good seal.

Gaskets required (this is for the KR/S V6)
1/ Throttle body to inlet manifold
2/ Gasket between air bypass and TB  Is a funny shape rubber "O" ring.  (this is the bit the coolant pipes connect to)
3/ "O" ring for the ISC Motor
4/ "O" ring for idle speed screw.  Mitsubishi do not list them but if you go to Bursons or Repco you will be able to get one the same size.
5/ Vaseline
6/ Carburettor cleaner, Wynns is the best one I know of.
7/ A small artist paintbrush for cleaning galleries, pref one that is horse hair and not painted handle as the carb cleaner will make a mess.


What to do:

Removing the Throttle Body.

  1. Remove the induction pipe, breather pipe and the air filter cover.

  2. Disconnect the throttle cable.Remove the 2 bolts under the rear of the TB from the mounting bracket. (12mm)

  3. With the engine cold, remove then replace the radiator cap to ensure there is no pressure in the cooling system.  You will now be able to remove the 2 coolant pipes and if you are careful you should not loose any coolant.  You can plug these to stop coolant loss if you wish.

  4. Disconnect the ISC motor wiring and the TPS wiring, be careful not to loose the metal clip that retains the plugs.

  5. Remove the 4 Retaining bolts (12mm)

Dismantling the Throttle Body.  
  1. Remove Throttle Position Switch

  2. Remove air control valve (be careful of the screw heads as they are prone to be very tight. If this is a problem tap a hammer on top of the screw driver to help loosen them)  You may wish to secure the TB in a vice but be very careful and use some soft pine to insulate it from the vice jaws.

  3. Using 8mm socket, loosen and remove Idle Speed Motor.

  4. Remove Air Screw.

  5. Give throttle body a VERY good clean with card cleaner paying particular attention to the air bypass passages etc

  6. Give air valve a good clean again paying particular attention to air passages. hint when cleaning through passages a small artists paint brush is ideal. Make sure it is a good one so the carb cleaner does not dissolve it.

This is the area you will need to get nice and clean.  If you do not intend to dismantle the Throttle body, ensure this is the area that is cleaned.  This can also be done while the throttle body is still on the car

Reassembling the Throttle Body.  
  1. Reassemble the air valve and isc. I ALWAYS use new "O" rings and gaskets which in total will cost about 20 dollars. You will find if you use the old  gasket between the throttle body and air valve will swell being rubber. if this happens and you do not have a new one handy use a tiny bit of Vaseline to hold it in place.   Do not use bearing grease as it will damage the rubber.

  2. Refit the TPS.  To set the TPS, open the throttle and place a .5mm feeler gauge in the throttle stop. using a multimeter set the TPS so it is "just" open circuit with this minor opening. (pin 1 & 3 on TPS)


While cleaning disconnect battery. when all has been re assembled hold foot on acc to floor, turn ignition to on without starting and hold here for 30 seconds. this will reset isc motor.

Start car and bring up to operating temp. stop engine and bridge wire in engine bay behind left strut tower, is usually a beige one but check if unsure. this will turn off the isc. Mitsubishi states idle should be 700 in neutral but I have found it is better at around 850. Only use air screw to adjust as the throttle stop screw should never be touched.  (hint, on some models this plug is in different places, fine someone who can show you the right plug and ALWAYS us a fused bridge wire)

I hope this is a help. I have done the many many times and in 95 percent of cases the you would never tell the car is running after this has been done

Madmagna : Sunday, 24. August 2003 19:25:08