Cadillac Sputters Untill 30 MPH

I have been looking at buying a 1990 Cadillac Sedan Deville as a fixer upper. For some reason up until 30 MPH it sputters really bad, it doesn’t stall, just sputters. It gets so bad to the point of you’re shaking back and forth in the seat. Above 30 it runs perfect. The owner took it to a shop and they replaced the throttle position sensor thinking that was the problem but it didn’t fix a thing. Does anyone have any ideas?

They want $100 for the car so I figured its worth a shot to get it running half-ways decent for an around-town car.


Is the problem strictly speed-dependent, or do throttle opening and load enter into the equation?

and how does it idle?

I would try the spark plugs and wires first, as my car had a similar problem. Turns out the di-electric grease on the wires gooped down onto the plug connectors due to engine heat and poor application of grease by the factory. After just cleaning off the tops of the plug connections on the wires and plugs with alcohol swabs, the car ran perfect. Air/Fuel/Spark=combustion. Maybe next try O2 sensor in control of A/F mix.

you can tell when it idles that it does have a slight misfire but when driving its a lot worse

Get a price on the engine computer. If it has the $100.00 one, buy the car and try rebooting the computer by disconnecting the battery. If the problem goes away for a day or two; maybe change the computer. It may take two or three tries to accomplish it. If you have an expensive computer, give up and don’t go near the wreck. Be cautious because any part under the hood is at least $100.00. We ain’t dealing with no fine piece of machinery here.