2G Annoying S90 idle problem adjusting ISC steps

PearlSweatshirt · May 29, 2016

Okay so I've searched everywhere for this info and I've come up with nothing I'm getting so irritated with this.

My problem is this: replaced both the isc and tps on my tb. Before I proceed I wanna say that my car has been heavily modified (also have an s90 70mm tb) I have the car on a flash tune. But here's the thing when I log via evoscan to monitor my isc steps with my tps at 5% at idle my isc steps will sit comfortable at around 20 or so.

Then when I go to adjust the biss to increase it to 30. I will set the biss adj mode. Adjust it. Then go back in to log and when I do it will sit at 20 and slowly drop to 0 when it does that no matter which direction I adjust the biss it will stay at 0.

Any ideas on this?

second_amendment · Jun 4, 2016

sounds like you might have a possible air leak

911gdsmboostin · Jun 4, 2016

Think the biss is too be at 30 at idle with tps at 0 percent and .63volts tps but that's 1g specs with ecm link. Also I have to simulate mine and the biss also sits at zero at times but also moves up around 30 and fluctuates but idles fine for me. (Stock 1g tb)

Peso · Jun 4, 2016

PearlSweatshirt said:
Okay so I've searched everywhere for this info and I've come up with nothing I'm getting so irritated with this. My problem is this: replaced both the isc and tps on my tb. Before I proceed I wanna say that my car has been heavily modified (also have an s90 70mm tb) I have the car on a flash tune. But here's the thing when I log via evoscan to monitor my isc steps with my tps at 5% at idle my isc steps will sit comfortable at around 20 or so. Then when I go to adjust the biss to increase it to 30. I will set the biss adj mode. Adjust it. Then go back in to log and when I do it will sit at 20 and slowly drop to 0 when it does that no matter which direction I adjust the biss it will stay at 0. Any ideas on this?

Check your egr vavle and also check your air hose for leaks

DSM B · Jun 4, 2016

What was the reason you replaced your isc? Was it shorted? If so, your drivers in your ecu could be fried. I would check the coils in your isc for shorts... If so you may need new drivers in your ecu.

PearlSweatshirt · Jun 5, 2016

So I've replaced my ecu. My tps and my isc. And I'm still having the same problem my steps aren't wanting to stay up they just drop to 0 after awhile. Although iam getting codes on my ecu. One is an mdp sensor, heater coil for my rear o2 and one other one for my Evap but i don't see those having to do with is

DSM B · Jun 6, 2016

To start I would check the wiring to the isc from the ecu.
Was the ecu you replaced a new or reconditioned ecu? Or was it used? The reason I ask is because if used the drivers could still be bad causing the problem...
I would also verify the coils on the isc are good. I had a brand new isc and I tested the coils before installation and they were good. Installed it and several hours later I started getting the same issue as you are describing. I kept telling myself the isc must be good because its brand new. Tested it later and found a shorted coil. I had to send my ecu back for inspection and found bad drivers again. They replaced them and I exchanged the isc and it worked as it should.

PearlSweatshirt · Jun 6, 2016

Thanks for the info! I will look into that but first I'm going to reset my tps and see maybe if it's out of adjustment

And the ecu was a used black box out of a stock 99 gsx

I've heard ppl say the tps needs to be at 5, 10 and 0% during idle so I'm a bit confused tbh

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