What is the normal RPM idle for TBI?
 

Hey guys, I am curious about the idle of my TBI. I had a tired roller 305TBI from the 1991 Caprice (the 305 with the missing air cleaner.) Normally it idles at 750rpm, which is not to bad for a worn out 305. a year later, My dad boosted the timing way too high for the tired TBI (18 degrees of timing) and the highest idle was 1,100rpm, it was so high that it drove itself. Turned it down to 650rpm and timing backed down to 12. The 305 lasted another month and then overheated. So then I got a rebuilt 350 4 Bolt from a local junkyard, did the long block swap, swap the Throttle body and adjusted the timing to 16 degrees. (the picture with the engine all black and 84 T/A air cleaner) Now read closely, we left the idle screw alone, never been touched. so when it reaches operating temperature, it idles down to 500rpm (the pic of tachometer) the strangest thing is that the 350 doesn't stall when I put it in gear. (The 350 does have an aftermarket flat tappet cam, a little aggressive but not much)

So should I turn the idle up a hair or leave it alone?

I'm curious because on cold days the 350 idles at 700 to 750 rpm and on warm days, it idles at 490 to 500rpm.

Re: What is the normal RPM idle for TBI?
 

if it is a tbi then the timing needs to be put back to about 4 to 6 dgrees. the ecm will then take over. are unplugging the timing connector when setting the timing?

Re: What is the normal RPM idle for TBI?
 

"Stock" idle is ~500RPM. Set timing to 0 with ETS unplugged. You most likely need 350 injectors and a custom chip (at least a stock 350 chip).

Re: What is the normal RPM idle for TBI?
 

Actually I didn't set the timing, my father did. He adjusted the timing with person holding the brake, dad under the hood holding the throttle and turning the distributor up. But I never saw him unplugging the connector while adjusting the timing. After he adjusted it, I was hearing the popping sounds while it's idling so I told him to back off the timing. It only pops when it's cold but once it warms up, the engine smooths out. I am also curious that why does the engine feels like it hesitates at stock timing but takes off like a drag racer at advanced timing?

Re: What is the normal RPM idle for TBI?
 

What kind of a fuel pump are you running? i dont think the stock unit that came on a 305 tbi car is going to support a cammed 350. when you did the swap did you change the injectors? i believe stock l03 injectors are 40lb/hr... l05 is 55lb/hr. There are a few other things to switch when doing a 350 swap... did you do them all? Its not a good idea to advance the timing that much. 4* advance would be good, but make sure you set it properly. I believe one92rs was referring to the EST. you can find it on the passenger side fender in the engine compartment. It should throw a SES light when unplugged. goodluck

Re: What is the normal RPM idle for TBI?
 

The fuel pump is the stock 305 TBI pump. Didn't change the computer. But we did change the throttle body. My dad got the 350 Throttle Body out of a di9fferent 350. I'm afraid to lose power by setting it back to 4* so I will leave it alone. I just want to know if I can still let it idle at 500rpm or I would have to raise the idle up to 750rpm.

Re: What is the normal RPM idle for TBI?
 

ok i am having a idle problem also. i have a stock 305 tbi as far as i can tell. the car runs good but when its warm it idles about 1200 in nutrual. . the tach is factory but way off have no clue how to get that right. i have the car hooked to a computer to check water temp an idle speed. from what i gather from reading above the rpm should be about 500? an timing about 4 degrees advance. i am going to do a tune up an adjest the timing an c where i am from there . does this sound right

Re: What is the normal RPM idle for TBI?
 

305s are supposed to idle at between 500 and 750rpm, If it is idling at 1200rpm when it's warm, that's too high. There's the idle screw on the driver side of the throttle body.

http://s15.photobucket.com/user/slam...re045.jpg.html

As for timing, Yes Go with 4 degrees advance. Get a timing light to see where you are at. Don't try (Unless you want to) to set your timing at 16 degrees like mine because you will have to make sure the engine doesn't stall once you put the trans into gear.

Good luck.

P.S. As for the tune up, go with ACDelcro plugs. Best plugs for Gen 1 engines.

Re: What is the normal RPM idle for TBI?
 

this is way late,

but if you haven't fixed it, pull the est plug, you cant set the timing on a computer controlled engine by ear like in the days when carbs ruled

i mean you could get it close, but its better to pull the plug and adjust to 0, work up slowly from there in 2* increments until you are happy with idle