1987 Jeep Cherokee Jerks over 55mph

I have a 1987 cherokee laredo 4x4 with a 4.0l. When get to speeds over 55 mph it will suddenly jerk what feels like forward. It only seems to do this after a while at these speeds. I have been told that it could be the Throttle Position Sensor (TPS). But before i start repalcing stuff i would like some more opinions.

Mine used to buck and jerk right around 2000 RPM, it would usually get over it, if I accelerated through the 2000 RPM envelope. It turned out to be the O2 sensor. It also crapped out well below redline. It also hunted quit a bit at idle, it couldn't seem to make up it's mind what RPM it wanted to idle at.

h20polobubbles said:

I have a 1987 cherokee laredo 4x4 with a 4.0l. When get to speeds over 55 mph it will suddenly jerk what feels like forward. It only seems to do this after a while at these speeds. I have been told that it could be the Throttle Position Sensor (TPS). But before i start repalcing stuff i would like some more opinions.

Click to expand...

It could be but whens the last time you put a new fuel filter on that puppy?

my 88 XJ would jerk at 70 mph, but if I drove 65 no problem. I finally took it to the dealer and had the senior machanic work on it. He found I had a sticky EGR vavle. He replaced it and the problem was fixed.

Also while we are talking EGR have you ever replaced the hoses that connect to the valve cover? My owner's manual says to change them ever 52,000 miles. I recommend you change them if you are unsure of the age. The front assembly comes in two halves and replaces nearaly every vacuum hose used on the engine.

I finally had my EGR stick open and my MPG dropped to 15 mpg, I was 500 miles from home so I drove it home and sucked the the extra gasoline costs. I recommend you examine the EGR. I will say the dealer EGR was bascially the same cost as the Autozone EGR. I felt more comfortable with the dealer part. The mechanic used one of those scotch brite pads on a rotary drill to clean up the manifold surface before he installed the new gasket and EGR.

If you suspect a bad TPS, buy a cheap analog mulitmeter if you don't already have one(the kind with a dial) and unplug the sensor. Measure between supply and output using an ohm scale- you are looking for a nice smooth change as you move the throtle plate. If the needle jerks around, it's no longer good. I'll see if I can dig up some numbers.

Might want to check your fuel pump. Hook up a pressure gage to the fuel rail and see what kind of pressures you are getting. Could also be a presure regulator problem. Had similar thing happening to my XJ and turned out to be fuel pump. If you want to check your TPS someone posted this the other day on how to do it and numbers for it.
http://xj.sequoiasite.com/tech/autotranstps.pdf