Throttle Body (TB) maintenance on injected Vettes is essential but often overlooked. This device is THE primary interface between the driver and the vehicle. It controls air flow to the motor, sensing for the computer via the TPS, a vacuum port and a fresh air port for the PCV system.

Several issues can arise with throttle bodies. Most of these are in the form of vacuum leaks. The obvious places are between the TB and plenum, vacuum port and the bellows seal (although the bellows is before or outside the TB, air entering here is unmetered and therefore not compensated for by the ECM which may result in lean condition / vacuum leak symptoms, especially in Open Loop). Some not so apparent locations include a bad seal at the Idle Air Control Motor / Valve, poor top plate sealing, poor IAC / Coolant cover sealing ( I have actually had some vehicles pulling coolant into the engine through the IAC passage) and worn shaft bushings. If you suspect a vacuum leak perform a visual inspection of the lines, etc. and also check the TB shaft bushings by trying to move the shaft front to back &  up and down (without rotating it). If you have not serviced the TB in a while, it may be a good idea to remove it and clean it up. When you remove the TB, look at the gasket surfaces of the plenum and the TB and if either of these surfaces has oxidation, there may have been a vacuum leak.

There are other problems that one may come across with throttle bodies. I have run across a few with shafts that bind. Essentially there is a resistance to the shaft rotating open and closed. This condition may be caused by corrosion build up on the shaft or improper bore alignment.  Weak return springs have also been known to keep the blades from fully closing. When checking these conditions it is a good idea to disconnect the throttle and cruise control cable. Also, on stock TBs that have been bored out the screw holes for the IAC/Coolant housing can be exposed on the plenum side in the bore. Use RTV on any of those screws to keep coolant out of the intake. Be sure to check this if your TB has been modified in this way. I have also seen some modified TBs that are not properly aligned and the plates are not centered in the bore and they bind against the bore wall.

If you decide to service your TB keep a few things in mind. Make sure to remove the TPS and IAC motor from the assembly so you can soak the aluminum components without damaging these devices. When disassembling, it is very likely, especially if the TB has been on the car for a long time, the screws holding the IAC housing may break. Soak the unit with ZEP Preserve or some other penetrating chemical to help loosen up these screws. Often times this helps, but even using this approach or applying heat is not enough. To help with this USM has a stainless screw kit (USM# U0111) which includes both the top and bottom covers. This kit can save you a ton of time and money the next time you service your TB.  We also have the full TB gasket sets for all years which include the IAC gaskets. Check out USMRacer.com. Also, inspect the IAC/Coolant cover. I have seen a few of them in which the external wall of the coolant hose barb was deteriorated and pitted. In fact I had one where the wall broke through while cleaning the corrosion off. If this is the case either bypass the TB coolant passage or replace the IAC/Coolant cover.

When reassembling the TB it is a good idea to take a small amount of RTV to put just a thin film on the gasket surfaces. In time the gasket gets hard and the RTV helps maintain the seal. Also, be sure to reinstall the IAC motor while the TB is off the car. It’s much easier. Before you put the IAC on, it may be necessary to retract the pintle. Check with your shop manual. After the TB is on the car hook up your hoses & don’t forget the vacuum line on the bottom. Connect IAC motor. Attach the TPS and adjust. Be sure not to over torque the TPS screws. Make sure it reads properly at wide open throttle (WOT) position as well as closed and that there is no binding. Connect the throttle cables and if an ASR car you should calibrate this as well. Start the car and warm it up. If all is well let it cool down and snug all the bolts and screws. Now reset, if necessary, the minimum idle speed and you are good to go.

If you have any questions or comments, please do not hesitate to ask. Thanks and Drive On!