This tech. article explains how you can convert a 1990 OEM throttle body into a performance one. Reasons for doing this modification would be to have a clean looking TB, eliminate idle surge, and to achieve a slightly higher performance TB. Best of all no stop light stalling. Basically same effects as a blocked off isc and fiav but better. Some disadvantages to this modification would be that your idle will sit at slightly over 1,000 rpm, cold starts require you have your foot on the gas, little idle regulation, and not emissions legal.
* Masking tape
*Two hours to cut and grind
*Six hours to fill and let JB Weld dry
*One hour to regrind
*Twelve hours to fully cure
I did this modification with a 1990 N/T throttle body.
1. Remove all sensors on the TB and the throttle cable spring system. Then reroute your coolant lines that were going to the TB.
2. You need to remove the lower portion of the throttle body which unlike 91+ can not be screwed off. To do this you need to cut with preferably a hack saw, the cut line should be about 1/4 inch from the bottom mounting bolts.
3. With the two halves separated now you can grind off the extra emission air inlets and smooth out any casting on the out side of the TB. Tape off BISS air inlet and outlet before grinding.
4. Once you are satisfied with the appearance you can mix some JB weld and fill in all of the holes on the TB except for the BISS valve inlet and outlet. I placed masking tape on the inside of the TB were the large holes are located to stop excessive running.
5. After five hours of dry time it should be ready for grinding, remove any of the JB weld that went through the holes on the inside of the TB. Then remove and shape the JB on the outsides of the holes to your liking. Here I removed the raised edge of the air inlet that is for the old isc. Refill any air leaks and repeat.
6. Once the JB weld has had plenty of time to dry clean, to remove shavings, reinstall with a new gasket or you can reuse the old with RTV on it.
7. Now you must adjust your idle, the BISS screw will be in almost all the way.
During summer the idle stays solid at 1000 rpms and during the winter the engine needs to be warmed a little before driving (5 min.) but still idles steady and my car has not stalled once for six months now.
I except no responsibility if this does not turn out good for you also. If you need any help PM me any time.