89 cherokee jerking while cruising on highway

[Zac ravioli]

My stock 1989 Jeep Cherokee 4.0 with a 4speed automatic has been doing a rapid jerking/nudging while its maintaining speed only happens above 55mph and I have been trying to figure it out since I got it about a year ago. Rpm and gear doesn't affect it as long as im going above 55 the engine also sounds like its running at a consistent rpm. Ste strange part is once out of every 50 times I get on the highway it doesn't do it the entire time but I didn't do anything different

 

[Goose_XJ88]

What have you done to try and fix it?
Try cleaning your throttle body, clean the IAT sensor, adjust your TPS.

I had bad surging and backfire on my 88 a while back going freeway speeds and a certain throttle input. Unfortunately I dont recall what fixed my issue.

 

[Zac ravioli]

Ive tested and adjusted the tps, cleaned the throttle body, replaced the iac valve, egr valve, crank sensor, o2 sensor, spark plugs, ignition coil, spark plug wires, most of the vacuum lines, and the fuel injectors. most of the things I've listened aren't directly trying to solve the issue but its still weird that after all that it still won't go away

 

[Anak]

Could it be a driveline issue?

Remove the front driveshaft and see if that changes anything.

 

[Zac ravioli]

update: since I put in the new vacuum lines and adjusted the tps its gotten worse but its also changed now the problem is happening when i cruse at 45-50mph and its making the car hop makes me think there's some sort of transition or computer issue

 

[lawsoncl]

Is it perhaps the torque converter locking and unlocking? Does it stop if you lift the brake pedal up or lightly press with your foot? That would point to the white switch high up on the brake pedal being misadjusted or dirty. As cruising speed, lightly tapping the brake pedal should trigger the trans computer to unlock the torque converter and the rpm should jump a few hundred rpm.

 

[Simonak3000]

Any updates on this? I seem to have the exact same problem, except I didn't change anything yet, just checked the TPS voltage and the CPS resistance. I will try the brake light switch this weekend

 

[lawsoncl]

On the older Renix era Jeeps, there are two switches on the brake pedal. One for the brake light and a white one higher up on the pedal that's for the transmission and cruise control.

 

[Simonak3000]

On the older Renix era Jeeps, there are two switches on the brake pedal. One for the brake light and a white one higher up on the pedal that's for the transmission and cruise control.

Mine is a 98. Is there still a brake switch on these?

 

[lawsoncl]

1998 it's just the single brake light switch feeding everything.

 

[Simonak3000]

Not to try and hijack this thread but since it seems I have the same problem, maybe I can be of help. I plugged my ODB2 reader into it (mine is a 98) and saw that the jerks/buck I was getting ROUGHLY corresponded with a drop in the MAP data (not always tho, sometimes it would jerk, but nothing on the map, and vise-versa). Yesterday I cleaned the throttle body along with the 3 sensors attached to it (MAP, TPS and IAC). That unfortunately didn't change anything. I then proceeded to check the MAP sensor with a multimeter, along with the corresponding pin on the PCU (pin 27). I even applied vacuum to it. Everything seemed to check out. That doesn't suprise me tho, since the sensor largely seem to be doing its job, except for these random drops. The drops also seem to correspond with a engine load drop too. I ordered a new MAP sensor anyway and some spark plugs, we'll see if that changes anything.