Idle/Return to idle issue and question
Hi all,
I've searched on the forum, among other ones, and haven't quite found the answer to my question. I've just installed the go street 400 on my 66 Fairlane with FE 390. It is mildly upgraded with performer rpm heads and intake, and has a 230/230 with 110 LSA roller cam. I get about 10" vac at idle in park and about 5-6 in gear. Cam setting is on 3 and idle set to 1000. I took it for a spin around the neighborhood and it performed flawlessly while cruising, however I have one issue left to work out.
When I go into gear, the engine will seem to "accept" the new rpm of around 650-750 for only about 5 seconds or so, then the system seems to start adding fuel/air as I can hear and feel the car starting to increase rpm, as if you barely start applying the gas while holding the break. It will do this indefinitely. When I put it into park/neutral, the rpm will sky rocket to 1800 and gradually come down. My IAC at idle will jump from 0-4 - pretty sure that's sorted. I've adjusted the 'loop rate down' all the way up to 40 and it seemed to help a little bit in terms of returning back to 1000rpm quickly, however the issue of this 'surge' while in gear and then shooting up to 1800 when coming out of gear still persists. I've experimented with putting it in gear for 1 or 2 seconds before this 'surge' can start, then putting it right back into park and it behaves as it should. I might creep up to 1200 for a quick second but it settles back down to the set idle rpm.
Question time - what controls this? Is this normal with other users with an auto transmission? What other parameters can I set/play with to get this shifting to park/neutral surge to stop? Thank you very much in advance!
Your IAC should be between 3-10 and not 0-4. Ideally jumping between 5-8 works great. Would suggest resetting IAC learn and reset IAC by adjusting the front and back screw. Most people just do the front. Improper IAC cause alot of issues including what you are experiencing.