PLEASE HELP ME (with my S3 2.9 idle problem)
Discussion
I have a 1992 S3C with the 2.9 Ford engine with electronic ingnition.
My problem seems to find its cause in the 'idle bypass valve', a cilindrical valve about the size of a microphone, sitting to the top front of my engine block.
When this valve is connected, my TVR runs almost 3000 revs when idle.
When disconnected, my TVR runs fairly normal, though not as smooth as should be. The real problem however is that the exhaust-emissions with disconnected valve are to high to pass MOT. So, until I find the cause, I cannot drive my TVR.
We have tried replacing the valve, a complete (computer-)diagnostic by a Ford-dealer and several other things, without any luck so far. So, before we start to disassemble the whole electrical system of the car: is there anybody in TVR-land that can give me a valuable suggestion, so I can continue to enjoy my Tivver???
My problem seems to find its cause in the 'idle bypass valve', a cilindrical valve about the size of a microphone, sitting to the top front of my engine block.
When this valve is connected, my TVR runs almost 3000 revs when idle.
When disconnected, my TVR runs fairly normal, though not as smooth as should be. The real problem however is that the exhaust-emissions with disconnected valve are to high to pass MOT. So, until I find the cause, I cannot drive my TVR.
We have tried replacing the valve, a complete (computer-)diagnostic by a Ford-dealer and several other things, without any luck so far. So, before we start to disassemble the whole electrical system of the car: is there anybody in TVR-land that can give me a valuable suggestion, so I can continue to enjoy my Tivver???
First thing to note is that disconnecting the ISCV automatically puts the ECU into "service" mode so normsl fuel mapping and many sensor inputs are over-ridden. In other words, if you disconnect the valve and the engine runs normally, it's not necessarily the valve that's at fault.
My first guess (and it's no more than that) is the engine temperature sensor (NOT the same as the temperature gauge sender!). If the ecu thinks the engine is cold it will enrich fuel and keep a fast idle. Disconnecting the iscv prevents the fast idle - you lose the symptoms but not the cause.
Also - mine does an odd thing that I've never cracked - if I disconnect the battery or the ISCV then reconnect, the engine then runs at a fast idle even when hot. If I leave the engine idling till the fan cuts in, then it idles normally, until the next time I disconnect the battery - is as if it has to reset a temperature "range" before it works properly. I don't know why mine does that, it just does.
Random ramblings but maybe helpful.
My first guess (and it's no more than that) is the engine temperature sensor (NOT the same as the temperature gauge sender!). If the ecu thinks the engine is cold it will enrich fuel and keep a fast idle. Disconnecting the iscv prevents the fast idle - you lose the symptoms but not the cause.
Also - mine does an odd thing that I've never cracked - if I disconnect the battery or the ISCV then reconnect, the engine then runs at a fast idle even when hot. If I leave the engine idling till the fan cuts in, then it idles normally, until the next time I disconnect the battery - is as if it has to reset a temperature "range" before it works properly. I don't know why mine does that, it just does.
Random ramblings but maybe helpful.
Edited by tvrgit on Wednesday 14th November 22:05
Have you considered that the throttle pot may be giving a wrong reading, ie telling the ecu that the thottle is open when it isnt,I realise this theory falls down in that your idle is okay with the valve disconnected but I would still try swapping it with a known good one, after all if the ford diagnostic check is showing all ok then logic has to go out of the window for a while.
Barkychoc said:
How about swapping the airflow meters over - isn't one used to measure the airflow and the other to measure the air temp? I know its a stab in the dark but its a free option to try.
Chris
S3C = no air flow metersChris
BUT could be a duff lambda sensor!
Edited by tvrgit on Wednesday 14th November 23:08
clarenceboddiger said:
Have you considered that the throttle pot may be giving a wrong reading, ie telling the ecu that the thottle is open when it isnt,I realise this theory falls down in that your idle is okay with the valve disconnected but I would still try swapping it with a known good one, after all if the ford diagnostic check is showing all ok then logic has to go out of the window for a while.
could be - disconnecting the ISCV may also make the ECU ignore the throttle pot input, if it's in service mode.tvrgit said:
Barkychoc said:
How about swapping the airflow meters over - isn't one used to measure the airflow and the other to measure the air temp? I know its a stab in the dark but its a free option to try.
Chris
S3C = no air flow metersChris
BUT could be a duff lambda sensor!
Don't swap the airflow meters you haven't got then !
Chris
Edited by Barkychoc on Thursday 15th November 14:01
hi another shot in the dark but i went through much of what you are saying and could not cure it but on about the 10th attempt i noticed that i could hear air suction noise i checked all the hoses round the servo and found an air leak at the bottom of the servo (rust) so i disconnected the servo pipe and blocked it off and all was fine, if you try this dont drive it just try it through the rev range standing still regards ken
It does sound to me like the ISCV is being opened when you connect it otherwise why would the revs rise? A quick way to prove this is to remove the valve and block the holes. With the ISCV connected and out of harms way start the engine and the idle should be low and a bit rough if it is cold. If that is the case then it is a matter of finding out why the valve is getting an open signal. I don't have a wiring diagram for the S3C so can't comment on that, but on teh S3 the ISCV links to the CPU and there is just a diode across the ISCV lines.
Someone mentions the throttle pot above and certainly they pot can be a funny beast. Not long after I had my car I had a problem with high idling at various revs - sometimes 2k sometimes 1.5k etc. I tried the standard tests of the resistance and sweeper output etc and all was working fine so I had it into a local diagnostic specialist which found nothing (you need your injectors cleaning sir - I'd been warned about that and no I didn't). I left it with them so they could cold start it, etc. but still no joy. In the end I took it to the TVR factory service people (they were there then) and they put it on their tester and found the throttle pot was working but giving off spikes which my static test didn't find. That was the problem - not like yours but it shows how testing them can be a problem as the people who did the initial work have a very fancy set up (apparently better than the one the factory used) and also train people in engine diagnostics but they didn't find it - "must have been a transient thing sir and no we won't refund any money ..."
- anyway my point after much rambling round is that the throttle pot is worth swapping with a good one if you know someone locally as they can have strange affects.
Jim
- anyway my point after much rambling round is that the throttle pot is worth swapping with a good one if you know someone locally as they can have strange affects.
Jim
It should be the Standard part I beleive,
Ford Motorcraft 6854780, this should be fitted (according to Ford) with the gold plated connector kit Ford Motorcraft 5028499.The connector kit comes with 3 small crimps to rejoin the cables when you have cut the old connector off, I would recommend soldering the wires instead and covering with heat shrink insulation as the crimps look as though they may have a dedicated tool to close them up and if the potentiometer is that fussy that it requires Gold Plated contacts I would be concerned about a crimped joint without the correct tool.
Ford Motorcraft 6854780, this should be fitted (according to Ford) with the gold plated connector kit Ford Motorcraft 5028499.The connector kit comes with 3 small crimps to rejoin the cables when you have cut the old connector off, I would recommend soldering the wires instead and covering with heat shrink insulation as the crimps look as though they may have a dedicated tool to close them up and if the potentiometer is that fussy that it requires Gold Plated contacts I would be concerned about a crimped joint without the correct tool.
PROBLEM SOLVED!
Thanks everyone for your help and suggestions. When I concluded that the throttle pot (in Dutch: gasklepstandsensor) was also a part of the 'idle rev' story, I immediately decided to replace this and ordered a new one at the local Ford-garage. After having fitted the new part, my S3C immediately idled as it should. With this problem out of the way, a positive MOT result was to be expected.
And now I am a happy man again...
Thanks everyone for your help and suggestions. When I concluded that the throttle pot (in Dutch: gasklepstandsensor) was also a part of the 'idle rev' story, I immediately decided to replace this and ordered a new one at the local Ford-garage. After having fitted the new part, my S3C immediately idled as it should. With this problem out of the way, a positive MOT result was to be expected.
And now I am a happy man again...
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