Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
Mentioned: 3 Post(s)
Quoted: 49 Post(s)
72W108 I have been unable to find my old parts list, but I will attempt to recreate it one system at a time.
For today, I have the parts for the idle air system. I chose to completely remove the idle screw and the associated thermo valve. If you remove those two items from the intake, you end up with a hole which is open to the coolant passage from the heads and you have two mounting holes where the idle screw were. In an ideal world, you would like to maintain the breathing of the engine the same and have a computer controlled idle. To do that, I fabricated a small (perhaps 2"x2"x1"tall) air box which mounts to the old mounting holes for the idle control valve. Into one side of the box, I ran a hose direct from the throttle body (where the old hose from the idle air and thermo valve attached). Into another side, I welded a metric nut with threads to accept the old breather element with the hose coming from the left hand valve cover. Out the back, the air box ties into the pipe that feeds into the RH and LH bank of the intake (where idle air used to go). On the top of this box, I installed the housing from the idle air valve from a Jeep 4.0 liter engine (part number 53032023AC). I replace the existing Jeep valve with a new stepper motor one (part number AC320) so I could use the stepper motor controls in Megasquirt. I believe the IAC housing is from a 4.0L jeep of the 1996 year range. I purchased a very cheap ebay jeep throttle body, kept the IAC housing and disposed of the throttle body.
So, on cold start, the MS opens the stepper the appropriate amount based on coolant temp. Air bypasses the throttle butterfly via my Jeep housing and air box and is fed to the individual cylinders as original design. The breathing of the LH bank is still as originally designed. As the engine warms up, stepper motor closes and controls idle at the determined speed. I also creep idle speed up a few RPM if coolant temperature rises above 200F.
The hole left by the old thermo valve is now covered by a 1/4" thick steel plate drilled and tapped to accept a GM coolant temperature sensor. I purchased my sensor with the connector from DIY autotune.
By the way, I purchased all my sensors and connectors with bare pins so when I made up my connectors, I was crimping to new pins, not splicing to pigtails.
Attached is a photo which shows what I just described