ReneH Posted December 20, 2023 Author Share Posted December 20, 2023 Bill - I see what you are saying and agree. My problem was that I forgot that the IAC/ISC only has one connection to the ECU. So yes, the circuits are as you are saying. Rene - Are you thinking you may have the diodes in opposing each other? That would cause real problems. Below is the 1996 EVTM entry showing the IAC and diode for 5.8L under 8500. Gary, Yes, it's possible, that I have connected the external diode opposite to the internal, if my IAC has an internal. I have connected it like shown in the 1986 circuit. When I've understood everything right on the FSB thread, the diode is shown there in the wrong direction... I'll check my wiring these days and also which pin on the 1994 IAC is the signal pin. Then I'll remove my external diode to see what will happen... I think it's most likely, that the IAC is not working, as I have had idle problems from the beginning... But I have no idea, how to check the IAC while it's installed... I may also clean the memory of the ECU to let it learn again. After that I should also re-do the idle speed procedure as I've done before. Link to comment Share on other sites More sharing options...
ReneH Posted December 23, 2023 Author Share Posted December 23, 2023 Gary, Yes, it's possible, that I have connected the external diode opposite to the internal, if my IAC has an internal. I have connected it like shown in the 1986 circuit. When I've understood everything right on the FSB thread, the diode is shown there in the wrong direction... I'll check my wiring these days and also which pin on the 1994 IAC is the signal pin. Then I'll remove my external diode to see what will happen... I think it's most likely, that the IAC is not working, as I have had idle problems from the beginning... But I have no idea, how to check the IAC while it's installed... I may also clean the memory of the ECU to let it learn again. After that I should also re-do the idle speed procedure as I've done before. Ok, I have had an error in my wiring... The IAC wasn't working at all. I have solved it and now you can see how it behaves now: Is this behavior common? The interesting thing is, that the metallic rattling when starting the engine at such high rpm is gone...maybe it's better to start at higher rpm to get more and much faster oil to the lifters? I have also connected the external diode. Without it the IAC acts very slow. So as it seems, is the diode for my IAC necessary. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 28, 2023 Share Posted December 28, 2023 Ok, I have had an error in my wiring... The IAC wasn't working at all. I have solved it and now you can see how it behaves now: Is this behavior common? The interesting thing is, that the metallic rattling when starting the engine at such high rpm is gone...maybe it's better to start at higher rpm to get more and much faster oil to the lifters? I have also connected the external diode. Without it the IAC acts very slow. So as it seems, is the diode for my IAC necessary. Rene - Sorry for the delayed response, but I've been traveling since you posted. Anyway, I'm not quite sure I understand what was happening in your video. Did you touch the throttle during the video? If not, I don't have an answer as to why it does that. In my experience the RPM should go high on initial start and then come down slowly as the engine warms up or time elapses. But it shouldn't go back up and then down as it appears it is doing. But it is good that you got the IAC working. That should make a huge difference. And perhaps as you drive the truck the ECU will learn how to control it even better. As for the rattling, I didn't hear it in the video. Is it possible that it was the IAC clattering that you were hearing? However, I don't think starting an engine and spinning it rapidly immediately is a good idea. I'd want to get the oil pressure up before doing that. Link to comment Share on other sites More sharing options...
ReneH Posted December 28, 2023 Author Share Posted December 28, 2023 Rene - Sorry for the delayed response, but I've been traveling since you posted. Anyway, I'm not quite sure I understand what was happening in your video. Did you touch the throttle during the video? If not, I don't have an answer as to why it does that. In my experience the RPM should go high on initial start and then come down slowly as the engine warms up or time elapses. But it shouldn't go back up and then down as it appears it is doing. But it is good that you got the IAC working. That should make a huge difference. And perhaps as you drive the truck the ECU will learn how to control it even better. As for the rattling, I didn't hear it in the video. Is it possible that it was the IAC clattering that you were hearing? However, I don't think starting an engine and spinning it rapidly immediately is a good idea. I'd want to get the oil pressure up before doing that. Hi Gary, today it was too late for the video of the new behavior of the IAC. I'll do it tomorrow morning... In the time between (and as the gas prices currently relatively low) I've checked my mpg... Driving only city and shorter tracks, I've got 12.4 mpg. I think when changing to an overdrive gearbox, it could be much better. Currently I'm driving relatively constant at about 2,500 to 3,000 rpm. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 28, 2023 Share Posted December 28, 2023 Hi Gary, today it was too late for the video of the new behavior of the IAC. I'll do it tomorrow morning... In the time between (and as the gas prices currently relatively low) I've checked my mpg... Driving only city and shorter tracks, I've got 12.4 mpg. I think when changing to an overdrive gearbox, it could be much better. Currently I'm driving relatively constant at about 2,500 to 3,000 rpm. If the ECU is learning then it should settle down after a bit. And if the idle comes down on its own then it is working correctly. As for the MPG, going to either an E4OD or a ZF5 should net you another 1 - 2 MPG. And it’ll make the truck seem more refined as the noise level comes down with the reduced RPM. Link to comment Share on other sites More sharing options...
ReneH Posted December 29, 2023 Author Share Posted December 29, 2023 If the ECU is learning then it should settle down after a bit. And if the idle comes down on its own then it is working correctly. As for the MPG, going to either an E4OD or a ZF5 should net you another 1 - 2 MPG. And it’ll make the truck seem more refined as the noise level comes down with the reduced RPM. Today I've recorded this video. It was at about 12 degrees Celsius when starting the cold engine: In my opinion this seems to be OK. What do you think? Link to comment Share on other sites More sharing options...
85lebaront2 Posted December 29, 2023 Share Posted December 29, 2023 Today I've recorded this video. It was at about 12 degrees Celsius when starting the cold engine: In my opinion this seems to be OK. What do you think? Looks about right. Sounds great! Link to comment Share on other sites More sharing options...
ReneH Posted December 29, 2023 Author Share Posted December 29, 2023 Looks about right. Sounds great! Ok, perfect...then I'm reassured:nabble_smiley_happy: You have to hear (and also see the faces) when I have to overtake cyclists and it's necessary to use the kick-down... In Germany V8s are very rare... Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 29, 2023 Share Posted December 29, 2023 Today I've recorded this video. It was at about 12 degrees Celsius when starting the cold engine: In my opinion this seems to be OK. What do you think? Looks and sounds great! Link to comment Share on other sites More sharing options...
ReneH Posted January 6 Author Share Posted January 6 Looks and sounds great! So, today I have rebuild my steering coupler: The damper is made from polyurethane, combined with a back-up disc made from stainless steel. I've done a test drive and it works great! All the sloppiness is out. Link to comment Share on other sites More sharing options...
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