Hi. Newbie here, first post. I have a '91 Grand Marquis w/ the 5.0L fuel injected engine and AOD tranny. I am experiencing engine hesitation/jerking when at part throttle maintaining speed. The jerking/hesitation is most noticeable while maintaining speed anywhere btwn 35 to 45 MPH. I do not notice the problem if I use cruise control at 60 MPH. My car accelerates fine with no hesitation/jerking. My TPS read 1.4V and I was able to modify/adjust it to 1.1V before I cracked the side of it w/ a drill bit. I replaced the TPS and now have a reading of 1.25V. I'm a little nervous about modifying the new TPS. The engine idles smooth and fine. I removed the screen mesh filter element below the PCV valve which was pretty caked w/ carbon build up. I checked the gap in my spark plugs and have them all adjusted btwn .48-.52. Being that the car accelerates fine I feel certain I can rule out anything distributor/plug wire related. I don't know if maybe the cause could be a transmission TV cable adjustment or what. I was hoping by replacing the TPS and double checking my spark plug gaps that it would solve the problem but it persists. I removed the upper intake manifold while I was replacing my heater hoses and noticed that it has some pretty bad carbon deposits. The hesitation is most noticeable when the engine reaches full operating temp. It doesn't matter if the car is in overdrive or not either. The car doesn't get driven a whole lot, only when I go home to visit my mother. Any ideas or suggestion on what I can try next? Sorry for the long post, but I wanted to provide as much info as possible.

Matt

 

Matt, A couple simple things I would check. Vacuum hoses for leaks, transmission fluid level, and a dirty throttle body. You may have checked these things but as simple as it sounds I would not overlook them.

 

have you cleaned out the IAC? ... changed fuel filter? ... might even have to go as far as dropping tank and changing the tank filter/sock that attaches to the fuel pump... i would think even possibly the TFI module might be on way out also... many things can cause the issue and it is a typical issue that can have many different possibilities

 

goood to see the post it is interesting.