I have a TPI on top of a ZZ4 in a 1970 El Camino. The BBK throttle body I have has a wonderful ability to suck itself closed hard just when the engine is running. Has anyone else had this problem and been able to fix it? I have tried opening up the blades by way of the idle adjustment screw, and that does work, but then I cannot bring the idle back down under 1000 RPM. The throttle works fine once it's cracked open, but I'm afraid that I'm tearing up U-joints because of the jolt everytime I try to get back on the throttle. It seems like engine vacuum is to blame. Are there any ports on the throttle body that would contribute to or alleviate this problem? I have the PCV run into the intake between the runners on the driver's side.

The car idles great when I set it down, it runs just fine at higher RPM's as well. I have an Accel Gen6 computer on it, so I can pretty much tune anything I want. My only option after this seems to be building a new gas pedal with a huge leverage ratio. Any other ideas?

Thanks,
Ryan

 

I would loosen the 4 screws that retain the butterflies to the throttle shaft, then open and close the throttle a couple times. After this close the throttle and use a screwdriver to lightly tap on the butterflies to make sure they are seated, then tighten them. If the butterflies are seated a little skewed they will hang on the throttle bores. You could also get some prussian blue (machinist's marking fluid) and find the high spots where the butterflies are hanging, and then take them down w/ emery cloth.

 

Did you reset the TPS after adjusting the plates open?

 

I had the same problem but only happened once the throttle body heated up. The cure was to bypass the coolant to the throttle body.

 

Are you still running an IAC?
Did you zero it out after resetting the blades open? Or ever?
What does the DFI say the IAC is at when idling in both instances?

 

Yes, the TPS has been reset each time to .5% per the Calmap instructions. The IAC is still installed and I run anywhere from 5 to 10% bypass air at idle - also per the Calmap instructions. I don't know how many counts that works out to, but it idles great. I do know that with the throttle blades opened far enough where the problem went away the IAC went to 0% bypass (closed), which tells me that there was no way it was ever going to idle with the blades that far open. Also, the throttle body coolant passages are bypassed and it didn't matter hot or cold.

I seem to have fixed the problem by just changing the ratio of the pedal arm. It seems the pedal for a 1970 Chevelle/El Camino just doesn't cut it for a TPI system.

I do have another question - my TPS only goes to 90.7% at WOT. This is far enough to kick the computer out of closed loop mode, but I'm wondering if I'm missing out on anything by not having 99.9%. Would a new TPS fix this? Does the BBK need a different TPS to work properly? I'm using a stock one I pulled off a stock throttle body. Again, it is set to .5% closed, but I don't know the voltages.

I appreciate all the responses!

Ryan