TBI distributor? FIRST thing to look at is the magnet on the mainshaft. They're often cracked, (usually across a rivet hole) creating a goofy signal to the ignition module. They're not replaced separately, you have to buy a mainshaft. I suppose someone could drill rivets, fabricate and replace the magnet, and then re-rivet; but I don't think that's a practical solution for a D-I-Y repair.
Make sure the mainshaft and bushings in the housing aren't scored/worn. Shaft should spin easily, but have no free-play in the bushings.
The grease-well at the top of the distributor housing generally has ancient, original "grease"* that's hardened and useless. If you screw-up the plastic cover/grease seal over the grease well, you'll have to make a replacement as GM has discontinued the plastic covers. Last I saw, the "Corvette" specialty suppliers were getting insane money for the few remaining grease seals. For the record, many aftermarket housings have a grease well and cover...but the housing isn't drilled so the grease has ZERO chance of lubing the upper bushing. There's no hole for the grease to travel through!
Assure that the vent screens on the underside of the housing are clean.
A fresh pickup coil is recommended.
*GM sold oil-wetted sawdust as distributor "grease" for awhile. They've also used white grease, and other products, too.
Make sure the mainshaft and bushings in the housing aren't scored/worn. Shaft should spin easily, but have no free-play in the bushings.
The grease-well at the top of the distributor housing generally has ancient, original "grease"* that's hardened and useless. If you screw-up the plastic cover/grease seal over the grease well, you'll have to make a replacement as GM has discontinued the plastic covers. Last I saw, the "Corvette" specialty suppliers were getting insane money for the few remaining grease seals. For the record, many aftermarket housings have a grease well and cover...but the housing isn't drilled so the grease has ZERO chance of lubing the upper bushing. There's no hole for the grease to travel through!
Assure that the vent screens on the underside of the housing are clean.
A fresh pickup coil is recommended.
*GM sold oil-wetted sawdust as distributor "grease" for awhile. They've also used white grease, and other products, too.