Cascade Crew

kutison · Posted: Fri Mar 20, 2009 6:12 pm Post subject: Reasons for a low idle

My 305 89 RS is idling low, at about 550-600 rpm and I was wondering what conditions would lead to that symptom. It is causing the car to occasionally stall, and/or the headlights to temporarly dim, If I let up on the throttle to fast.
I had a throttle body from a 350 on there for a while, and while it was fun, it was killing me on the gas, idling at 1250 and lurching when I shifted to drive.
Because I don't really know what I am doing unless I have lots of advisors, Whats most likely causing the problem, and what do I need to do to fix it?

Thanks guys, and or gals. Shocked

Dewey316 · Posted: Fri Mar 20, 2009 7:21 pm Post subject:

550 is the commanded hot idle, in drive, for TBI cars.

The dying and surging however, isn't normal. Does the motor run rough, or seem to be missing at all at idle?

kutison · Posted: Sat Mar 21, 2009 7:07 am Post subject:

well the surging stopped when I switched back to the 305 TB from the 350. It was so bad I actually managed to peel out just shifting to drive. The guys at the gas station thought it was pretty funny too.

As for the stalling, I couldn't say really. I haven't had this car for very long., and have never had another quasi-powerful car like this.

It's not a huge concern to me because it doesn't happen often, but I don't want it to get worse. And I am just trying to understand my baby.

they say knowledge is power and communication is key. And I like power and keys.

Twilightoptics · Posted: Sat Mar 21, 2009 10:45 am Post subject:

If you put a 350 TB on you have to reset the minimum air setting. The 350 blades will be open a touch more than the 305 blades and since the 350 TB is bigger, it will flow more even at an idle if un-adjusted.

Dewey316 · Posted: Sat Mar 21, 2009 4:59 pm Post subject:

350 TB is the same as the 305, the only difference is injectors.

Twilightoptics · Posted: Sat Mar 21, 2009 5:17 pm Post subject:

Thought I remember you saying it had bigger bores.

Dewey316 · Posted: Sat Mar 21, 2009 6:17 pm Post subject:

only the 454 TB has larger bores. The 350 one has the same bore as the 305, but larger injectors.

Granted, anytime you put a different throttle body on, you have to reset the min air setting on it. And with the larger injectors dumping fuel in, if there was a vac leak, the motor would rev up pretty good.

blue89 · Posted: Mon Mar 23, 2009 7:14 am Post subject:

Don't they group the TBI bore sizes like:
2.8/3.1
4.3/5.0/5.7
7.4

(just so I know)