Hi all. I have a 1991automatic with the 4.0 and am having trouble with the rpms dropping when going over bumps. The car will never stall or die but the tach will get close to zero. It happens anywhere from surface streets at around 30 mph to the highway at 65-70 mph. The transmission will lurch some of the time. I have an feeling that it is a sensor somewhere that is dirty or needs replacing but indomt have the time or money to replace every single one. Thank you in advance.

 

does it do it when you are on the gas over bumps, or only basically idling? If idle / basic idle, check the IAC. Otherwise, sounds like might be a loose wire at a sensor.