FIXED / HOW TO: IAC, engine dies when stopping, rough idle, TB bypass
Hello all, well my recently acquired LT1 bird just had it's first bug for me to iron out. I haven't picked up a wrench on any of my cars in over 2 years, so I was excited to have a chance to work on the car. I'm gonna post this so if other people have the same or similar problems, hopefully this will pop up in the search for them. I wasn't planning on doing a write up so the pictures are kind of scattered, but you'll get the point.
THE PROBLEM: Car had a super rough idle (no cam) and the engine slowly died when coming to a stop, or making 3 point or slow speed turns.
POSSIBLE CULPRITS: Idle Air Control Valve (IAC) or Vaccum Leak. I tackled the #1 suspect first, the IAC.
PROCESS OF FIXING: First thing's first, gotta remove the air intake system. My car being Ram Air was fairly easy, as a bonus I got to install my new K&N filter. Once your intake and mass air system are out of the way, it's time to un-plug all the tubes off the throttle body.
In order from top to bottom on the passenger side you have:
top- PCV tube (some oil might drip out of this one)
middle- vaccum hose that goes back towards the EVAP solenoid
bottom- stubby coolant line ran to the metal pipe runnig from the back of the passenger head.
On the driver side of the throttle body you have:
top- throttle linkage, to remove, just pull the cable to WOT (wide open throttle) and unhook the throttle and cruise cables.
Underneath that theres another coolant hose.
*** MAKE SURE YOU HAVE PLENTY OF TOWELS STUFFED UNDER THE TB AND ALL AROUND THE OPTI BEFORE YOU REMOVE THE COOLANT HOSES. COOLANT CAN AND WILL SPILL OUT AND RUIN THE OPTISPARK! ***
Once all your hoses and wires are disconnected, unscrew the throttle body x4 10mm bolts. You should now have a throttle body in your hand.
The IAC valve is sticking out of the bottom left side of the TB and held on by 2 torx bolts, unscrew them and it should slide right out. DO NOT MOVE THE PLUNGER IN/OUT OR TRY TO ROTATE IT, YOU WILL RUIN THE VALVE. Soaked the spring and plunger in wd40 for about 10 minutes, hit it with some carb cleaner, 5 QTips and compressed air, 125k miles of crud GONE.
Take some time to spray down the throttle body and clean that out too, be careful not to soak the TPS sensor, Carb cleaner can ruin electrical connections. Used some more QTIPS to get inside the IAC housing.
I opted to do the THROTTLE BODY COOLANT BYPASS at this time, since everything was apart. Very simple, remove the stubby coolant pipe from the pipe going to the back of the head. I removed the alternator bracket for easier access, 14mm attached to the intake and 2 13mm on the alternator side. Once that tube is removed, take the tube that was originally running to the driver side of the throttle body and plug it into that metal tube. This is the long tube coming from the coolant overflow by the radiator cap. Finished witht the bypass and it looks stock too, so I was happy with that.
Put everything back together in reverse order and it's almost finished. YOU HAVE TO RESET THE IAC. Press in the clutch (if it's a 6 speed) and press the accelerator to the floor, crank the engine for 10 seconds, turn ignition to OFF position, wait 5 seconds then start the car. DONE.
I hope this helps anybody who's car was suffering the same symptoms as mine.
__________________ TERRY - 1996 WS6 Trans Am T-Top M6
what year is your car? lol i seriously thought that the IAC was the black unit on top of the intake manifold right behind the throttle body plate in the first picture, where the green male pigtail plugs in, i guess im wrong lol...does anyone know what that is?
it only has the problem when cold & it tries to idle at like 150 rpm & will surge and die. I had the car in storage for 3 years and got it back out this summer. If having a disconnected battery for 3 years doesnt reset it then I'm not sure what would
__________________ 99 Firehawk #210 - Soon to be for sale.
Restored 68 SS350
03 Mercedes AMG SL55 Kompressor