fuel mixture

[squidgestir]

1990 Gti 2.0 DOHC 4wd 4ws. After changing my plugs i noticed that they are heavily carbon coated. It is also using a lot of fuel as the miles per gallon is only about 24-25. Can anybody please tell me if there is a way to turn the fuel mixture down so that it is running leaner.
I have a complete mitsubishi technical diagram of the rear suspension for this car, complete with the mitsubishi part no if anybody wants a copy, let me know and i will e-mail you a copy.

[manybrews]

no, there isnt a way to adjust it down, and even if there was, using the amount of carbon on the plugs is NOT any indication of how it actually running.
you need a 4 or 5 gas analyzer to do it correctly.
The car is probably running perfectly, but you need to know for sure before you attempt to lean it out, as you will melt pistons and the cylinder head quickly if you screw it up.

[ken inn]

are you sure the plugs are correct for the car? also, is the car equipped with an oxygen sensor? if the car is, the sensor could be bad. also possible that the engine temp sensor is bad, so the ecu thinks it is still in cold start/warmup mode, and running rich. if the car is o2 equipped, the ecu needs to see input from several sensors to go into "closed loop" mode, when it starts using o2 trim to adjust fuel. if it does not get the correct readings from these sensors, it will stay in open loop, and run off of factory preset fuel/timing maps. these maps are richer for safety, and have much less aggressive timing.

[MASONSTORM]

is the cel light on? if so, do you get a code? poss o2 sensor or valve seals are bad, fouling your plugs. any smoke out the tailpipe?

[squidgestir]

1990 Gti Dohc 16v
There is a screw on top of the throttle body with a cross head. This is set in an indented hole, when i turn this screw in the revs go down, is this just for setting the base revs at tickover??
Puzzled

[squidgestir]

Found out what it is!
Its called a BISSS. Which means base idle speed set screw. I found that to set your idle speed what you have to do is let your car reach operating temp. Turn your engine off, turn the screw in till it will go no more, then back it out 2 full turns. This should set your revs at around 750.
My idle busted in the first place because i have a faulty idle speed control unit(ISC), and it was allowing too much air into my throttle body. I solved the problem by taking off the throttle unit cleaning it, then rebuilding it without the ISC plugged in. I just adjusted my base revs using the BISSS. My car runs fine now at operating temp, its just a bit jumpy when its cold, but i quess thats a lot cheaper than buying a new ISC.

[manybrews]

A new ISC motor isnt THAT expensive.

and youre probably gonna notice issues when the car is heavily loaded electrically (all the lights on, AC on, etc).. since your idle cant compensate for the additional load, youll probably lug it somewhat.

[ken inn]

dunno about a 90 non usa car, but it sure sounds like you have a similar system as the usa cars. if your isc is electronic, then more than likely idle speed is controlled by the ecu. biss=BASE idle set screw, this is to set your BASE idle. then, the ecu has a range above and below base idle that the isc adjusts to. so, MANUALLY adjusting base idle is not the correct way. you need to override the ecu by grounding at least one connecter, usually found in the engine compartment, and possibly another inside the car, THEN set your base idle using the screw. this is with the engine running at operating temp. it is a good idea to also set base timing at the same time. on the usa vr4, timing is also controlled by the ecu, and base timing is critical.

[squidgestir]

I found an ISC in a local car breakers so i am going over in the next few days with an ohm meter to check it and pick it up. I also need a wheel sensor for my ABS system as well as when the car is stood the ABS light is off, but when i start to drive the light comes on. I have spoke to a mechanic and he says the problem is the wheel sensor. I have left the car with him so that he can check them to tell me which one is not working.
I have just spent £800 https://www.thegalantcenter.org/style_emoticons/default/sad.gif on repairing this car as it has been in my garage for the past 2 years, I know its worth it though https://www.thegalantcenter.org/style_emoticons/default/laugh.gif