What does this do exactly?
Discussion
There's a little screw on the 2.9 plenum, near the throttle linkage, and Nick had it adjusted at the rolling road as the car was hunting at idle, and it seemed fine. However, it suddenly started idling high @ 2000rpm. He cleaned the TPS and ISCV, but this did nothing. He then adjusted this screw, and noticed the car stalled, so he then began tinkering to get it to idle correctly. However, it is again idling high, at around 1500rpm, and it smells very very rich. The picture below shows the 2.8 engine, but it looks like it does exactly the same job. Any info is appreciated.
MJG280 said:
On a 2.8 A is the stop for the butterfly and B is the idle screw
It's A that I'm referring to on the 2.9, it effects the idle quite a lot, but I thought the throttle bodies would just close, as the ISCV controls the idle? Since the idle screw has been adjusted the car has had an odd idle, and now has refused to start; fouled plugs from lots of on/off with Nick adjusting the idle? Or something more sinister?I don't know about that engine management system, but typically the throttle stop needs to be adjusted so that the throttle plate closes fully, there is an internal bypass with a screw adjuster which sets the base idle and then the idle control system controls an additional bypass. If you try to adjust the idle by winding the throttle stop up so that the throttle doesn't close, the ECU senses that you have got the throttle open and doesn't activate the idle control logic. In effect you have disabled the idle control system.
Without knowing how that engine management system is supposed to be set up it's hard to know how to do that, but I'd start by resetting the throttle stop so that the throttle closes fully, and hope that you can get it close enough to the original position that the ECU recognises it as closed. This may not be easy unless you know / can find out what the TPS threshold is supposed to be. Once you have the throttle closing properly, you need to set the base idle via the air bleed adjuster screw. Again, best to find out the proper way to do this but if you can't find that out then I'd go for blocking off the air bypass via the idle control system and adjusting the air bleed until you get to somewhere around 500 rpm idle. That should put the idle control system roughly in the middle of its travel at idle. These systems don't have to be very far out of adjustment to mess things up, and if you can't get it sorted out I'd suggest you try to find an old school mechanic locally who has worked on Ford engines of this era and is familiar with setting the idle up.
Without knowing how that engine management system is supposed to be set up it's hard to know how to do that, but I'd start by resetting the throttle stop so that the throttle closes fully, and hope that you can get it close enough to the original position that the ECU recognises it as closed. This may not be easy unless you know / can find out what the TPS threshold is supposed to be. Once you have the throttle closing properly, you need to set the base idle via the air bleed adjuster screw. Again, best to find out the proper way to do this but if you can't find that out then I'd go for blocking off the air bypass via the idle control system and adjusting the air bleed until you get to somewhere around 500 rpm idle. That should put the idle control system roughly in the middle of its travel at idle. These systems don't have to be very far out of adjustment to mess things up, and if you can't get it sorted out I'd suggest you try to find an old school mechanic locally who has worked on Ford engines of this era and is familiar with setting the idle up.
GreenV8S said:
I don't know about that engine management system, but typically the throttle stop needs to be adjusted so that the throttle plate closes fully, there is an internal bypass with a screw adjuster which sets the base idle and then the idle control system controls an additional bypass. If you try to adjust the idle by winding the throttle stop up so that the throttle doesn't close, the ECU senses that you have got the throttle open and doesn't activate the idle control logic. In effect you have disabled the idle control system.
Without knowing how that engine management system is supposed to be set up it's hard to know how to do that, but I'd start by resetting the throttle stop so that the throttle closes fully, and hope that you can get it close enough to the original position that the ECU recognises it as closed. This may not be easy unless you know / can find out what the TPS threshold is supposed to be. Once you have the throttle closing properly, you need to set the base idle via the air bleed adjuster screw. Again, best to find out the proper way to do this but if you can't find that out then I'd go for blocking off the air bypass via the idle control system and adjusting the air bleed until you get to somewhere around 500 rpm idle. That should put the idle control system roughly in the middle of its travel at idle. These systems don't have to be very far out of adjustment to mess things up, and if you can't get it sorted out I'd suggest you try to find an old school mechanic locally who has worked on Ford engines of this era and is familiar with setting the idle up.
Ok, thankyou. When you said 'air bleed adjuster screw', what do you mean? I don't think there is one on this engine....Without knowing how that engine management system is supposed to be set up it's hard to know how to do that, but I'd start by resetting the throttle stop so that the throttle closes fully, and hope that you can get it close enough to the original position that the ECU recognises it as closed. This may not be easy unless you know / can find out what the TPS threshold is supposed to be. Once you have the throttle closing properly, you need to set the base idle via the air bleed adjuster screw. Again, best to find out the proper way to do this but if you can't find that out then I'd go for blocking off the air bypass via the idle control system and adjusting the air bleed until you get to somewhere around 500 rpm idle. That should put the idle control system roughly in the middle of its travel at idle. These systems don't have to be very far out of adjustment to mess things up, and if you can't get it sorted out I'd suggest you try to find an old school mechanic locally who has worked on Ford engines of this era and is familiar with setting the idle up.
King Fisher said:
Ok, thankyou. When you said 'air bleed adjuster screw', what do you mean? I don't think there is one on this engine....
The air bleed would be a connection from upstream of the throttle plate to downstream of the throttle plate. If it's there, I'd expect it to be integral with the throttle body. The air bleed adjuster screw controls the amount of air that can pass through it and would also be integral with the throttle body.GreenV8S said:
The air bleed would be a connection from upstream of the throttle plate to downstream of the throttle plate. If it's there, I'd expect it to be integral with the throttle body. The air bleed adjuster screw controls the amount of air that can pass through it and would also be integral with the throttle body.
Not sure there is one on this engine?Gerald-TVR said:
These might help
2.9 Throttle Body
Danke!2.9 Throttle Body
It seems that screw is just a throttle stop? But surely the throttle butterflies will close themselves and not go any further? And the ISCV should take over the idling? This is very confusing.
Edited by King Fisher on Tuesday 24th April 19:59
King Fisher said:
Danke!
It seems that screw is just a throttle stop? But surely the throttle butterflies will close themselves and not go any further? And the ISCV should take over the idling? This is very confusing.
Yes it is only a throttle stop, but the position of it is crucial to the 2.9 running corrrectly, if you read the diagnosis sheet kindly provided by norman then you will understand, basically the position of the screw at idle controls the voltage from the throttle pot and makes sure it is within range for the ecu, simples, good luck.It seems that screw is just a throttle stop? But surely the throttle butterflies will close themselves and not go any further? And the ISCV should take over the idling? This is very confusing.
Edited by King Fisher on Tuesday 24th April 19:59
Cheers.....Tony..
tozerman said:
Yes it is only a throttle stop, but the position of it is crucial to the 2.9 running corrrectly, if you read the diagnosis sheet kindly provided by norman then you will understand, basically the position of the screw at idle controls the voltage from the throttle pot and makes sure it is within range for the ecu, simples, good luck.
Cheers.....Tony..
Forgive me, I'm not that mechanically minded myself. So, Nick should measure the output of the throttle pot and make sure it is correct? If I'm reading the article correctly, the output from the throttle pot is 0.6 Volts at idle, and 4.5Volts at full throttle?Cheers.....Tony..
tozerman said:
yes, spot on. 
Cheers.....Tony..
Excellent, thanks for clearing that up. I take it that he could have sorted it purely by chance though? He has adjusted it and got it idling at around 850rpm (the reason he can't get it started again is due to a duff coil, last thing he checked!). Cheers.....Tony..
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