Adjust the BISS screw on a 1G TB

[hellotbone]

6bolt swapped car.

1G TB works mine question about adjusting the BISS screw to get my idle right car runs perfectly however every now and then coming off of RPM to a light say from 3rd to holding the clutch in and coast up it has the tendency to stall when you come off the gas for a second then catches its self. Is that just a BISS screw tweak or something else with the TB I gotta play with?

 

[Stapl3]

You have a boost leak.

 

[4g63awdtalon]

replace the seals in the throttle body, and purchase yourself a new biss screw, one of the best mods in history

 

[hellotbone]

Its a brand new rebuid I bought I was hoping it wasn't that no boost leaks I have a tester its not leaking anywhere forsure.

Maybe just play with the BISS screw a bit anyone have a base setting.

 

[CanadianTSi]

You're not venting your BOV are you?

 

[hellotbone]

Nope Im gonna play with the BISS a bit just no time yet anyone know the base setting?

 

[Rick4g63]

Try replacing it
http://www.machv.com/newbasidsets.html

If you have idle problems, check pcv, clamp connections and ISC.

Good luck

 

[hellotbone]

Its not an idle problem its a coming off of RPM problem when you come down from RPM to a stop. It idles fine when you start it or once it does the intital drop. Im guessing it just needs more air.

 

[steve]

The BISS and ISC interact. On a 1G you can ground the timing check and diag mode pins to lock the ISC in it's std position to adjust the BISS. On most 2G's you have to use the MUT to do the same thing.
Without it when you adjust the BISS the ECU adjusts the ISC to control the amount of bypass air to reach the target idle speed. If you don't set the BISS correctly then the ISC can be too far in or out to be able to emulate the dashpot on decel.

You can try using your datalogger to adjust the BISS while watching the ISC steps. I forget exactly what number of steps it should be at idle but my 1G runs fine at 20 steps. Perhaps someone can pipe up with the exact number.

Two other things that could cause the engine to die on decel are the speed sensor and the idle position switch. Did you use the 2G TPS in the swap? Did you adjust it by using the 2G procedure?

Steve

 

[hellotbone]

The BISS and ISC interact. On a 1G you can ground the timing check and diag mode pins to lock the ISC in it's std position to adjust the BISS. On most 2G's you have to use the MUTT to do the same thing.
Without it when you adjust the BISS the ECU adjusts the ISC to control the amount of bypass air to reach the target idle speed. If you don't set the BISS correctly then the ISC can be too far in or out to be able to emulate the dashpot on decel.

You can try using your datalogger to adjust the BISS while watching the ISC steps. I forget exactly what number of steps it should be at idle but my 1G runs fine at 20 steps. Perhaps someone can pipe up with the exact number.

Two other things that could cause the engine to die on decel are the speed sensor and the idle position switch. Did you use the 2G TPS in the swap? Did you adjust it by using the 2G procedure?

Steve

Thank you finally someone with a real answer. I did adjust the TPS ViA vfaq and also have had to adjust it a little more to get to 98% at wot just had to play. What is this MUTT you talk about never come up in any of my posts? If I start my car when warm it idles perfect how come only on decel it does it?

 

[steve]

I did adjust the TPS ViA vfaq and also have had to adjust it a little more to get to 98% at wot just had to play.

Which VFAQ and once again I ask which TPS are you using? You should have reused your 2G TPS. If you did then getting it to read 98% when at WOT doesn't matter. What matters is that the IPS built into the TPS opens and closes at the right spot so that the ECU sees that the throttle is closed.
If you used the 1G TPS then you have to rewire the TPS harness to connect to the 1G IPS.

What is this MUT you talk about never come up in any of my posts?

That's the Mitsu scan tool. From it you can tell the ECU that you want to set the BISS and it will lock it in the std position and not make corrections while you adjust the idle speed with the BISS. This way the ISC should be positioned so that it has enough range to perform dashpot emulation when you close the throttle.

If I start my car when warm it idles perfect how come only on decel it does it?

Because you have adjusted the BISS to idle. That doesn't mean you haven't driven the ISC out of range in the process, or that your IPS is switching at the right point to tell the ECU that the throttle is closed, or that your VSS is working telling the ECU that the car is moving so that it holds the engine speed up until you come to a stop. There are error codes for when these things are grossly out of whack but I suspect there can be problems before any codes get thrown.

Your problem may be none of these, but this is what I'd look at. Since your idle dips and then corrects itself, I'd guess that the problem is the ISC is closing all the way on decel because of the way you set the BISS. I'd try turning the BISS in a little more (less idle bypass air from the BISS and more from the ISC) and see if that helps. I'd also go back and check how you adjusted the TPS.

Steve

 

[hellotbone]

Thanks steve for all the info. I actually swapped out to my old auto trans ecu and it works flawelessly now. Wonder why maybe diff in ECU's?