Finally fixed wierd idle

[baxsom]

I have been having a wierd idle ever since I installed all my upgrades (PF, new TB, 3" exahust etc) and I have never been able to track it down until now.
When cold the idle would surge up and down. When hot it would idle fine. I attributed it to the egr pipe being removed to accomodate the portfueler. Not so. The new 55mm throttle body was the culprit. The idle screw which is normally out a few threads was backed all the way out. I checked the old TB on my pocketlogger and it gave an idle position of 11%. The new TB gave a position of 6%. Once I screwed the idle screw in to the correct reading and reset the ecu it idles perfectly. I guess that the IAC was working over time to compensate.

 

[markGSX]

I have been having a wierd idle ever since I installed all my upgrades (PF, new TB, 3" exahust etc) and I have never been able to track it down until now.
When cold the idle would surge up and down. When hot it would idle fine. I attributed it to the egr pipe being removed to accomodate the portfueler. Not so. The new 55mm throttle body was the culprit. The idle screw which is normally out a few threads was backed all the way out. I checked the old TB on my pocketlogger and it gave an idle position of 11%. The new TB gave a position of 6%. Once I screwed the idle screw in to the correct reading and reset the ecu it idles perfectly. I guess that the IAC was working over time to compensate.

haha, i hate that screw... it tends to back out with normal engine vibration. there's supposed to be a factory cap to secure it in place, but the dealer wanted like 8 bucks for the rubber cap. WTF
I've heard of some using a dab of RTV to hold it in place.

 

[steve]

The factory plug isn't intended to hold it in place, it keeps the road crap from getting it and the water out so it doesn't corrode the BISS. It's the o-ring that keeps it from self-adjusting.

The reason why the car surges with the BISS so far out is that during warmup the ISC is normally all the way closed from right after starting to when the car reaches 186F and the FIAV closes. Only the FIAV and BISS regulate the bypass air while warming up. If too much air gets in the RPMs go too high and the ECU cut off the fuel causing surging.

Steve

Steve