My '89 came with an aftermarket BBS throttle body, which I believe to be the cause of off-idle stumbling the car suffers. I want to remove it and put a stock piece back on. Does anyone know if the differences between models years are significant enough that I cannot "shop around" by year a little? Or must I acquire a 1989 piece specifically?

In short: What years of stock throttle body will work on a 1989 L98?


p.s. It's just absurd that anyone would buy a bigger throttle body for an engine that makes its max power at 4,700 RPM...

 

1989-1991 are all going to be the same throttle body.

 

Sort of but not quite.

1989 shows a unique part number for the throttle body kit (17112126), while the 1990-1991 show different throttle body kit (17112385). The Idle Air Control (IAC) valve shows the same for those three years (important since it implies that the IAC pintle is the same on the bottom of the TB), but the TPS shows a different part number for 1989 vs. '90-91.

So check to see if you can find an 1989, and if you can't then I'm sure the other one will also fit - but you'll need to research any small differences on sensors, etc.

 

The difference in TPS sensor is the 89 is adjustable and 90-91 are not. They will physically mount to the throttle body the same way. The difference is in how the ECU handles the reference signal.

 

Is it feasible that the relevant components could be swapped from my current aftermarket assembly onto one from the wrong year to replicate the '89 layout? I mean are these like a base casting that was constant with the changes made to the pieces attached to it?

 

Yes, they are going to be the same casting, Move the sensors over and it'll be good to go.

 

With respect to the '89-'91 years, Yes I think you could get away with that. The IAC is the same, which as I mentioned above is really important because the IAC housing casting on the bottom of the TB has to have the exact right shape for the IAC valve that you're using. They varied slightly over the years.

Spencer's info above I agree with. The '90-91 ECM will figure out full closed throttle plate position based on range of motion / voltage, whereas the '89 ECM wants to see .540 volts (+/- .070 tolerance) at full closed throttle.