Decided to take a break from being at school, and went home to install new injectors and a Holley TB on my 87 TPI setup. Against my best training, I decided to change two variables at the same time, assuming the result would be positive. To shorten the story, I ended up putting the old injectors back in after disassembling the intake twice.

The engine runs fine at speed, but surges from 600-900 RPM at idle, and the exhaust note is very rough and spluttery. I reset minimum air and adjusted the TPS per instructions in the tech articles. I tried the propane trick to look for vacuum leaks, but wasn't able to locate any (though I don't have much experience with this method). Only changes to the intake are a Holley 52mm TB and IAC housing heater bypass (didn't want to corrode the new TB with engine coolant). I just installed the IAC housing without the heater lines connected.

I used fresh gaskets on the intake, and verified all vacuum lines are connected and all unused ports are plugged. I've about run out of ideas other than putting the stock TB back on and seeing if the problem persists. I tend to suspect the throttle body assembly, since the setup ran similarly both times.

Thanks for any help that can be offered. I'm building an ALDL cable when I get home for summer, so I may be able to make a better assessment then.

 

Did you install a TB designed for the early TPI intake plenum?

 

At low rpm, you go from low kPa to 100kPa with very little throttle movement, making driveability 'worse'. For example, with a very large throttle body you may get 100 kPa at 20% throttle at 2000 rpm. This means if you want to hold it at 40 kPa for cruise, you have to be very steady on the throttle, as small movements may produce large changes in engine output (so it's harder to be smooth), and
A small throttle movement (and a small V/sec TPS signal change) can result in a very large change in MAP (as mentioned above) at low rpms. The result is little (or no) accel enrich when the engine needs it most. However, you can usually tune around circumstances like this by richening the VE table at low rpms and higher kPa (say < 2500 rpm and> 70 kPa) by about 5-7%. This has a negligible affect on fuel economy, since you likely never see 70 kPa while cruising.