ECMlink Need help with idle surge after going to Speed Density

[Built4g63t]

Well just got back from shopping and it still did the idle surge but its weird cuz its not doing it all the time. Where would you suggest to hook a vac gauge up to? I have a vac boost gauge td off the fpr. As far as the o2 sensor where would I start with checking wires?

 

[Built4g63t]

Do you think the throttle body shaft seals could be leaking would that cause idle surge? Why would the surge stop when I disconnected the idle switch?

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[steve]

Why would the surge stop when I disconnected the idle switch?

That I can answer. I alluded to it before but I'll explain. Idle Surge is really Deceleration Fuel Cut happening at idle. There is a section of code in the ECU that looks at the engine RPM and checks if the throttle is closed (is the IPS closed), if it's over a defined RPM and the butterfly is closed the ECU turns off the fuel injectors while the engine winds down and then turns them back on to keep the engine from stalling. When it does this while driving you don't normally notice unless you have a lightened flywheel or issues with your ISC. But if the car can't idle correctly and the RPMs exceed that trigger while the throttle is closed it does the same thing and you wind up with surging. Whit the IPS disconnected it can never meet the condition for Deceleration Fuel Cut since the ECU thinks the throttle is always open.

Usually this is caused by some sort of air leak but there are other less common causes.

 

[Built4g63t]

Ahh that makes since. Now my next question is if my problem is a air leak going on why would the problem not be there all the time? It never has the idle surge when cold it seems to only happen after its warmed up after driving for little while. I think im going to switch out my throttle body with the other one I have and see if the problem is still there.