IAC possibly?

**redline** · 02-26-2006, 07:41 PM

any of you all ever have sudden increases in rpm at a stop light. It only happens in open loop with ac off and defrost off. The motor runs about 600 rpms warm and sometimes bumps to 700 or so and then back down. Its not really a problem just seems to be happening more frequently lately. Thought it might be the idle air controll but dunno, what do you guys think.

**SeVeReDiStOrTiOn** · 02-26-2006, 08:17 PM

IMO that's normal....odds are it's the fan kicking on or disengaging. The sudden current load can slightly change rpm....every f-bod i've owned has done it. The open loop comment is kinda throwing me though. You say it runs at 600rpms warm...a motor at running temp is in closed loop...so i'm guessing you just meant closed loop. Are the rpm's changing when it's cold or warm...and does it do it all the time....like up down up down in a row? Listen for the fans engaging(listen close because the low speed fans are quiet) and see if the rpms change. And if you want you can pull the IAC and spray it with carb cleaner...

**redline** · 02-26-2006, 08:39 PM

im sorry i ment to say closed loop, and yes when its warm 190degrees or so. It dont happen consistently just maybe twice or so at a long stop light. The problem is its happening more and more frequently. At first like you i thought it might just be the fans. Ive been a mechanic for about seven years now and unfortunatly dont get very much ls1 work so im fairly new to the family if ya no what i mean. Just good to hear it happens to you as well.

**Baluchitherium** · 02-27-2006, 05:13 PM

I do get what your describing,and it happens to me when my fans kick on.Nothing major at all just a very small jump in RPM as they kick on.

It could be happening more often now because outside temps have kinda been on the rise maybe?Just a thought....