I have an 89 Caprice wagon with the buick 307 (w/carburator). I has 76K miles. When I bought the car it ran great. I has gotten progresively worse.

It has a rough idle (feels like it is missing) and bad fuel milage and now is dieseling at shutoff. It started around 21mpg and now it is at 10 mpg.

I have changed the plugs, wires, cap and rotor. I'm not sure where to go now.

I can't seem to find a way to set the timing. does this thing have a computer?

Can someone help me out?

I'm no expert but when I bought my '89 caprice sedan w/ fuel injected 305 the mechanic of dealer that I bought the car from said he'd never seen so much carbon build up in car before. They had done a lot of work in the top part of the engine to get the thing to run. In doing so they physically removed carbon deposits from the engine as well. Now every couple of oil changes I'll run Sea Foam through the gas tank and the injector/carburetor. Once a year I also buy a can of 44K to add to the fuel. I notice a big difference in idle and fuel efficiency after I use these cleaners. This is the cheap easy fix though so no guarantee.

take a couple of cans of carb cleaner spray directly into tbi with engine off open throttle completely then crank engine it may take a minute dont worry then spray into throttle body while running youll need to keep the engine running (give it some gas) then pull off one vacume hose at a time spray into them keep engine running dont forget brake booster vacume line

check your exhaust components too!