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SN95 Cobras
car dies when coming to stops at random?
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<blockquote data-quote="mwolson" data-source="post: 10719501" data-attributes="member: 16006"><p>Sorry to disagree, but this will treat the symptom, but not the cause. You can accomplish the same thing as drilling a hole by adjusting the throttle stop screw to open the TB blade a hair. But that will then probably screw up the idle system.</p><p></p><p>SVT Pille, you will see if you datalog your idle that it is probably now out of kilter. You want to see your ISC duty cycle to be around 35% and the ISC integrator to be around 0. Your tuner should know this. You set your ISC duty cycle by slowly adjusting the TB stop screw while datalogging. Your tuner should then set the ISC integrator to 0 by adjusting the idle air tables in the tune.</p><p></p><p>The PCM uses air for coarse control of idle, and it uses spark advance for fine control of idle. You will also want to log your spark source to see if it is at a steady 9 when you idle. That means spark is in control of idle.</p><p></p><p>Idle problems can really be difficult to solve. If you try to solve them without datalogging, you are just shooting in the dark. And the first thing to do is ensure you don't have any leaks of metered air with a smoke test before you even start trying to fix idle issues.</p><p></p><p>However, the OP's problem is not an idle problem, it is a deceleration problem. I have seen this in cars that have larger than stock injectors, and that is solved by tweaking the dashpot function in the tune. </p><p></p><p>I have also seen the lack of a good VSS signal at the PCM cause this problem. The PCM uses a more aggressive dashpot function when the car is stopped than it does when the car is moving. If the PCM does not see a good VSS signal, it thinks the car is stopped and drops the RPMS very fast. But the load on the engine from the power brakes and steering is too much and causes the engine to stall. So this symptom can also be caused by the lack of a VSS signal to the PCM.</p></blockquote><p></p>
[QUOTE="mwolson, post: 10719501, member: 16006"] Sorry to disagree, but this will treat the symptom, but not the cause. You can accomplish the same thing as drilling a hole by adjusting the throttle stop screw to open the TB blade a hair. But that will then probably screw up the idle system. SVT Pille, you will see if you datalog your idle that it is probably now out of kilter. You want to see your ISC duty cycle to be around 35% and the ISC integrator to be around 0. Your tuner should know this. You set your ISC duty cycle by slowly adjusting the TB stop screw while datalogging. Your tuner should then set the ISC integrator to 0 by adjusting the idle air tables in the tune. The PCM uses air for coarse control of idle, and it uses spark advance for fine control of idle. You will also want to log your spark source to see if it is at a steady 9 when you idle. That means spark is in control of idle. Idle problems can really be difficult to solve. If you try to solve them without datalogging, you are just shooting in the dark. And the first thing to do is ensure you don't have any leaks of metered air with a smoke test before you even start trying to fix idle issues. However, the OP's problem is not an idle problem, it is a deceleration problem. I have seen this in cars that have larger than stock injectors, and that is solved by tweaking the dashpot function in the tune. I have also seen the lack of a good VSS signal at the PCM cause this problem. The PCM uses a more aggressive dashpot function when the car is stopped than it does when the car is moving. If the PCM does not see a good VSS signal, it thinks the car is stopped and drops the RPMS very fast. But the load on the engine from the power brakes and steering is too much and causes the engine to stall. So this symptom can also be caused by the lack of a VSS signal to the PCM. [/QUOTE]
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car dies when coming to stops at random?
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