I’ve been dealing with an inconsistent idle for a while now and I’m stumped on what could be causing it. I tried setting my BISS screw through EvoScan, but when I deactivated the SAS actuator, the idle surged badly. I had to adjust the screw manually without EvoScan to get a reasonable idle, but it still surges occasionally. I also noticed that when the idle dips to around 850 RPM, the engine sometimes runs lean. I’m unsure if this is just a tuning issue or if there’s an underlying mechanical problem.

What I’ve Done So Far:

• Throttle body rebuild
• New idle control valve (ISC)
• New intake manifold gasket
• Multiple boost leak and smoke tests (everything checks out—no leaks)

The car has a new 2.2L motor with slightly bigger cams (Kelford 272 → GSC S2), so I know it needs a tune. However, I want to make sure I’ve ruled out all potential mechanical issues before tuning.

Here’s a link to a video showing my attempt to set the idle with EvoScan:

 

Do you have an Omni 4bar MAP? A lot of us have had those fail and cause weird stuff like this.

Otherwise, I would just test the ISC to make sure thats good, set the BISS correctly with the SAS off and get a tune. I bet that it needs some fuel and timing adjustments at idle for the new cams and whatnot.

 

Yes, I do have an Omni 4bar map it was replaced too not long ago. I'll go ahead and test the ISC but yeah I'm hoping it's a tune issue.

 

To clarify, you’ve had a 2.2 in there before with the 272s and you have had that tuned, but you need it tuned with the S2s on the new motor?

I have Kelford 272s and it idles like absolute trash if the base timing values are off. I’m not intimately familiar with the S2 profile but my guess is that is where your issue is, assuming you have no boost leak issues, a functioning IACV and a good 4bar.

Another possibility is a dirty MAF if you aren’t running SD.

 

So the tune was for my 2.0 with the kelford 272s. When I put my new 2.2 with the s2 cams I was told I could break it in with my old tune. I'm gonna do another boost leak test on Friday to confirm and ill also test my IACV too.

 

another vote for Omni MAP. theyre trash