Idling Problems

[Francine]

I know this has been touched on before but my problem is a little different.

My Felicia 1.3LX was idling at 700 - 750 revs, but under braking the engine just cut out, repeatedly. I went to see my friend who tried to fix it 'temporarily' and tightened my throttle cable and squirted carb cleaner (which I wasn't happy about) into the throttle body. It then started idling at 2000 - 2500 revs, it then started reving higher and higher. I returned the throttle cable to where I thought it was, (it is now really loose), but then it was idling at a screaming 3500 revs. I've unpluged the block plug (I have no idea what it is for as I'm no mechanic) on the throttle body and its dropped the revs back down to around 2000 revs so I could get it home.

So from tightening the throttle cable to loosening it again my idle has totally gone haywire. I could really do with a little advice on what I need to do to get it back right again.

[daverapid]

Does your car have a carburettor, single point injection or multi point injection? Either way, check the inlet manifold gasket, any vacuum hoses and in the case of carb and SPi models the gasket/rubber block between throttle body and inlet manifold for leaks. Also, if your car has a carb make sure the carb earth connection is good.

[Francine]

Its multi point injection.

I already checked the rubber block between the throttle body and the inlet manifold and all the hoses and there all good.

Edited 26 July, 2009 by Francine

[TeflonTom]

try disconnecting the battery for a couple of hours, it may reset the idle speed after that

[bazz2004]

I suspect a serious flaw in the design of these cars because there are so many posts related to it. Mine tries to cut out when I stop unless it's fully warmed up but no one has located the fault. Ecu readings are fine. Other manufacturers' cars we've owned have had safety recalls. It's a bit late for these old models but cutting out at roundabouts, traffic lights and junctions is never good. At least mine restarts instantly. Just possibly water getting in around the well by the wipers and causing extreme wet areas behind the dash may have had something to do with mine. It's now better sealed and is almost dried out. Time will tell.

[Francine]

I disconnected the battery but nothing has changed.

I've unpluged the block plug (I have no idea what it is for as I'm no mechanic) on the throttle body and its dropped the revs back down to around 2000 revs so I could get it home.

Could someone please tell me what the larger block plug is on the throttle body? Unplugged the car is idling much better than it being plugged in but I can't go anywhere in it. Does anybody know if my throttle body needs replacing or if it is something else???

Edited 27 July, 2009 by Francine

[TeflonTom]

ok, i dont ant to blind you with the in depth workings of the idle system, but under the black cover on the side of the throttle body is 2 variable resistor tracks which wipes round as the throttle is actuated, one of the tracks is the main load signal to the ecu which is then used along with some data from other sensors to 'work out' how much fuel to chuck in, the second track is to determine the idle position(angle) of the throttle pate, ok so the reason you need to tracks is because as the idle speed (throttle position) also affects the singal from the load sensor track, so the ecu subtracts the idle postion from the load signal, so you always get the same voltage output range(no throttle - all the way to foot on the floor) irrespective of idle position.. quite a complicated system really

the idle speed itself is regulated by a simple stepper motor, basically the throttle plate is spring loaded so that the spring pressure is allways trying to close the throttle, the motor is 'pulsed' (pwm) by the ecu at a fairly high frequency which forces the plate open a little, so in essence the faster the pulses occur the more it opens the throttle, typically the range of possible idle speeds is quite low.

also within the throttle body is a set of closure contacts (switch) which are closed when the throttle is closed and open when the throttle is open.

so in reference to your question the plug is there to relay signals about idle speed and load to the ecu, i've thinking about this a little and if you think about it and break it down into simple science, for the engine to run you need air fuel and sparks, theoretically if the plug is disconnected the engine will run, but at a very low speed because not enough air is coming in (remember the throttle is never fully closed, there is a small base amount of air coming through, which leads me to think that either something is holding the throttle open such as the cable being incorrectly fitted or maladjusted, or there is something downstream of the throttle body allowing air into the engine such as a leaking core plug in the manifold, a split gasket/hose/vacuum connection or the map sensor is leaking or there is a small possibility that the throttle plate got jammed open when you originally adjusted the cable..

squirting carb cleaner in wont do any harm tbh, although it's possible a piece of filth could have been dislodged and is jammed the throttle open, but i would say that this would be sucked into the engine when it was running...

apologies for my essay, i'll go back to my cage now

[Francine]

That is brilliant, I understand the workings of it now. I'm really thankful you've taken the time out to write all that out as I've been struggling finding out the info I want.

[Cepheuz]

TeflonTom post make me wonder, if clean out the throttle body, the spray it with contact cleaner i think it would go back to the normal idle, and cable should be loose, but just a tad loose