okay here is my issue i have a 1992 chevy astro van with the 4.3liter v-6 it is TBI vin:Z okay the engine idles good when cold but when it goes into closed loop the engine will idle at 350-400 rpms in gear but off idle the engine feels strong does not hestate very smooth just the rough/low idle when the engine is in closed loop i have done a full tune-up plugs,wires,cap,roto,pcv,air filter,fuel filter and cleaned egr valve and change oil and filter. i have been told it could be my coolant temp. sensor, o2 sensor or the idle air control valve??!! and how do you test the IAC valve?? PLEASE HELP!!!

 

If you take the air cleaner assembly off the top of the t-body above the iac beside the throttle bore is a small square/rectangle if you look in there you should be able to see the iac end . You may want to remove it and clean the tip and the passage. If you have a scan tool you can look a the iac count (postion / %). Some scan tools you can command the iac to move. Also once it is closed loop turn as many acc. on as possible rear defrost , high beams ,a/c etc the iac should keep the idle up as the load is increased.

 

For the 1992 model year, the 4.3L had its block design modified to allow a balance shaft to be installed. Even though the 4.3L is an even fire V6, the 90 degree block layout is not ideal for smoothness. The balance shaft on the 4.3L is installed above the top timing gear, and runs through the top of the lifter valley. It is gear driven off the timing chain, and therefore a new timing chain cover was designed for these balanced 4.3L V6s.