Technical High idle and possible high emissions

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Technical High idle and possible high emissions

dumbledore

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I am trying to solve a high idle condition again.
The symptoms are that the idle sits around 1200k fairly constant but fails to get down. I did some emission measurements with some diy meter and emission were high. I checked lamda sensor and that looked dead so I changed two weeks ago. The emissions went low but the idle did not get down. So today I had another look. Checked the operation of the idle stepper motor and that is OK, also checked the coolant sensor and that is also OK. Rechecked to lamda and that is also OK, there is volage there around 0.9V flactuating. This indicates the engine is running rich at idle, and yes my diy gas analysed confirms CO around 4-5%, which is too much.
My suspicion is that the SPI injector may need replacement as my symptoms suggests that idle mixture is too rich. The ECU may be compensating by keeping the idle speed high to keep CO at lower levels.

Do you think the SPI injector failure is sound?
Anybody tried to to replace the SPI injector here? Can the SPI injector be serviced? I know MPI injectors can.
Can the injector be bought without buying the whole throttle body?
 
It's just an injector, so it can be cleaned and tested. Probably are new ones still out there.

Still, steady high idle almost always means an inlet (vacuum) air leak. On SPI cars it's often a leak from the bottom of the TB, else an issue with one of the hoses (even the servo hose).

Remember that the emissions will be high until the fan has gone on and off a couple of times.
 
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Thanks Fingers,

I cannot be 100% sure for the vacuum leak but I don't think there is any leak. All lines are OK.
I also done a vacuum test with the a vacuum gauge and the vacuum at idle is about 18-20hg, which is not suggesting there is a leak. Also there are two vacuum pipes going to the inlet air box. One small bore and one large bore. If I disconnect the small bore from the air box and then block it the idle goes temporarily to 1000rpm, but I drive the car like that for a bit the idle goes high again, and the emissions are still on the high side.

I am planning to remove the injector from the throttle body so I can inspect it without removing the throttle body. Is this possible and little risk job, or will I need a new throttle body if I get it wrong?
 
Cheers, again,
I'll source a another throttle body before I attempt to do anything just to be on the safe side. I'll keep you informed with my progress on this problem.
 
yep, there is a small clamp holding the injector down - once removed it pulls out easily. Careful not to damage the o-ring, may be good idea to just replace it. There is not much you can do other than pop it in a ultrasonic cleaner.

I'd be inclined to just try fitting another complete TB unit sourced from a scrappies or online before i started pulling out injectors though - they are only a few bob generally from scrap yard. And if you not got any, get some paper gasket so you can cut some new gaskets - do one for the gap between the injector part and butterfly part of the TB and under the TB where it meets the spacer - spacer to inlet should be fine but a light smear of instant gasket there can't hurt. Had a few leak from these areas over the years without touching them.
 
Cheers Blu for the additional information.

I have ordered a throttle body from a scrappy and should get it soon. I shall dismantle it to see how I get to to the injector safely and how to fabricate the gasket you are mentioning. I then will try to do the one on the car.

Starting to doubt that my injector is faulty though, but need to have a good look at the replacement throttle body to get some more ideas.
 
Yes, possible. But where the extra air comes from. The vacuum lines are OK. May be the gasket Blu is mentioned is gone on the throttle body and air goes in from the side. Can't see, but when I get the replacement throttle body will be able to see if this is possible. Also may be the throttle flap needs readjusting as there is a adjuster bolt there but to me it looks stack so don't think that bolt has moved at all to take the flap out of adjustment.

I will have to remove a spark plug to see if I have a overfueling or underfueling condition.
 
its 100% possible to leak in the middle or base of the TB, i have had it happen and read of it happening to others as well. If you are really sure none of the pipes are leaking or split etc that should be your next move in my view.

The plugs should look fine really unless one of the sensors is sending a false reading to the ecu - the ecu will adjust the mixture to be correct but if there is more air than expected for idle it will add some fuel to compensate and this is what results in a higher idle, its not got anything to do with it being rich or lean (or it won't if we assume all the electronic bits are working correctly). It running too rich or lean would be the result of a poorly coolant temp sensor or lamba probe generally speaking.
 
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Got the part today. Unfortunately it only contains the throttle body and not the injection part. However, I can see how the two parts (the throttle body and the injector holder part) are hold together. it seems that the two long bolts that are holding the air box on top of the throttle body also bolt the throttle body in place so it should be safe to remove the injector part only and see if I can service the gasket. Hopefully this is my problem.
 
OK, I had some more thoughts, and come across to a doubt about the gasket between the throttle body and injector body. If that fails I cannot see that that causes high idle, as the gasket is before the butterfly of the throttle and that should not cause excess air to go into the engine.

The assembly below the the throttle body may leak though, but there is no gasket?
 
Yes, the image is not clear but that part contains two parts. Nr 5 is the part that holds the injector and is connected to the bottom part the actual throttle body by gasket. The guy from the scrap yard only send me the bottom part.
 
yep, i was more talking about the leaking from the base really, but while you have it off it makes sense to redo the middle gasket too being that the two halves are only held together with 2 plastic clips even if you just apply a smear of instant gasket to the join. Leak from the middle is less likely to cause an issue but can do still if its not a steady leak if that makes sense.
 
May be have fixed this.
I decided to have a look at the bottom of the throttle body, and with it fitted I could clearly see the side of the two gaskets either side of the spacer. The gaskets from the side looked good. i started the engine and felt with my hand around it and could not feel any sucking. So I concluded the gaskets may be OK. I then decided contrary to Fingers suggestion to start adjusting the stop nut on the accelerator cable. And yes I can adjust the idle speed in this way. I managed to set it to 1K now. I will give it a go and see if this is OK for the engine. If not I can reverse the adjustment so the idle goes to 1.2K.

My feeling is that this may be a good fix though. Because with high mileage the butterfly to throttle clearance may increase resulting more air to pass by the closed butterfly and causing higher rpm. By closing the butterfly with the adjuster a bit then the airflow gets restored to original. The adjuster may be also be used in an emergency even when a vacuum leak is present so to compensate for the air sucked into the inlet around the butterfly system by the leak.
 
I wonder how the ECU works on the punto SPI. From what I can see it seems not to try to bring the rpm down when idle is high 1.2K. So I have the feeling it will act only if the rpm fall below 1K and then try to recover things to stay around 1K. This is quite the possible scenario for punto SPI as there is no sensor that tells the ECU that it should idle. Some cars but not punto SPI have a switch that when in idle the ECU knows there is idle and can act both ways bringing the rmp down and up so the rpm is maintained to 1K. As the punto SPI does not know the engine should idle a slightly open (more flowing throttle) is a valid condition and the engine will just maintain rpm 1.2K in my case. The rest of the sensor lamda, etc will then be used to keep emission to required spec.
 
So, find me a factory manual that advises adjusting the throttle stop. :)

You'll see it on all carbed cars. Never seen it for a car with EFI. (Except on early Bosch systems, where it's a set up step only.)

And, then, why should the throttle stop suddenly go out of adjustment?

Either the throttle butterfly isn't closing (for mechanical reasons ) dirt, tight or sticking cable or an inlet side air leak.
 
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