hello ive tried longing through post but no luck so if there is a topic on this im sorry. so i have a mostly stock 1996 cobra. runs fine and no codes 1st off. but when you come to a stop or push the clutch in the rpms hang around 1100-1300 for around 4 seconds before dropping to about 800.. i have checked for vacuum leaks but dont seem to have any. sprayed starter fluid all over the lines. i have also replaced the IAC. still no luck. any ideas or is this normal for the cobras?
idle problem
- Thread starter Jo Jos 96 Cobra
- Start date
ah ok then. now i know thanks you
a little long over due update. after having it up for the winter as spring has came around started diging back into the car a little more. changed the iac and the tps and made sure it was set to .98 still had same problem. only after doing more checking after the car was warm i have around 4 vacuum leaks around the upper intake. does not do it when the cars cold. so going to order new gasket and see if that helps
In our cars, setting the TPS has no effect. The PCM learns the characteristics of the TB where ever it is set and then calculates a value called TPS relative which it uses as the throttle signal.
so since i had to order the gasket you think the leak nite be my idle
A vacuum leak can cause a lot of idle issues. You need to fix all vacuum leaks first.
To know for sure your idle is working correctly, you need to datalog your idle. You should see a Spark Source of 9 which means spark is in fine control of idle. You want to see an ISC duty cycle around 30-35% which means that the IACV can do coarse control of the idle. If you have a custom tune, you want to see the ISC integrator around zero, or your IACV transfer function is off in the tune.
Here is a log of my car rolling to a stop. It shows the TP Relative in light blue which shows you when I let off the throttle. It shows you the vehicle speed in black as it rolls to a stop. It shows you the RPMs in yellow, which shows how the PCM holds the idle up around 1200 RPM until about 2.5 seconds after a complete stop. At that point, the spark source in green jumps to 9 and the idle drops down to about 800 RPM. This is how your idle is supposed to look.
If you can get access to someone with an SCT handheld, you can download LiveLink software and check the actual health of your idle.
Your vacuum leaks will show up with the Spark source not being 9, and your ISC duty cycle will be down around 0.
To know for sure your idle is working correctly, you need to datalog your idle. You should see a Spark Source of 9 which means spark is in fine control of idle. You want to see an ISC duty cycle around 30-35% which means that the IACV can do coarse control of the idle. If you have a custom tune, you want to see the ISC integrator around zero, or your IACV transfer function is off in the tune.
Here is a log of my car rolling to a stop. It shows the TP Relative in light blue which shows you when I let off the throttle. It shows you the vehicle speed in black as it rolls to a stop. It shows you the RPMs in yellow, which shows how the PCM holds the idle up around 1200 RPM until about 2.5 seconds after a complete stop. At that point, the spark source in green jumps to 9 and the idle drops down to about 800 RPM. This is how your idle is supposed to look.
If you can get access to someone with an SCT handheld, you can download LiveLink software and check the actual health of your idle.
Your vacuum leaks will show up with the Spark source not being 9, and your ISC duty cycle will be down around 0.
Last edited:
Ive had my fair share of TPS probs with my 96, sometimes its just the nature of the beast. Mark thats good info^^.
been thinking of getting a handheld tuner so i can keep a backup tune. car only does this after it warms up. cold start no vacuum leaks and normal idle and after warm temp high idle and vacuum leaks around gasket to upper lid
any sct better than others? can find a good deal on sx3 or am i better off getting the sx4?
Users who are viewing this thread
