I need some idea's. I put a high compression 355 al heads and mild cam under my 305 TPI, added new bosh 26lb injectors. the engine runs good while driveing but the idle when out of gear is hunting from 550 to 1300 and will die, in gear it idles between 570 and 650 rpm I did the min idle adjustment disconnecting the IAC after 30 sec and the lowest idle was 1300 rpm started at 1700 THE wb O2 is12-13 afr in open loop. (no hunting). the directions say to adjust idle to 450 rpm. I did change the bin file to 26lb injectors. any ideas on how to lower my idle? I think that because I can't get the min idle down is why it idles so bad .(the ecm having trouble controling it?) Thanks for any help

 

I cleaned the IAC motor and the car was worse, so I went to the chevy dealer and bought a new IAC. It ran or idled better but still surged and died. so for now I just turned the idle adjustment screw in until I had 800 RPM that was enough to stop it from dieing. I still would like some help on why I can't get the idle to do the min Idle adjustment!! Please

 

Surging/uneven idle is generally caused by lean AFR. You say it idles well in open loop at 12-13 AFR. Need to figure out what's changing as it drops into closed loop. The key player there is the O2 sensor. Your wide band should reveal if AFR goes lean in CL.

One other cause I've seen for surging idle is EST timing control. The problem has been solved with a new distributor. Also, check wiring to the dist and between the dist and ECM.

 

Thank you for replying. The engine stays about 14.7 when it goes closed loop. no the problem is at start up ,even when I drive it for 20 min stop the engine for 10 min then start again. It's in open loop when it surges in closed the ECM tries to keep the idle at 650 but it will drop to 580 then up to 700 ,but after driving 30 min the idle will keep a steady 620 when I come to a stop. do you have any idea if the gaskets on the intake tube to pendalum were switch if it could cause an internal vaccum leak ? I'm trying to get my head around why I can't the idle to come down past 1300 on the min idle adjustment, it's like the engine is getting a lot of air with the TB blades closed ? I can use any Ideas you have thanks again Mike

 

Did you disable the ECM timing control when setting the minimum air rate?

 

Do you need to disable the timing control when setting the minimum air rate? My problem is that I can't get the minimum idle below 1000rpm with the iac valve disconnected.