'87 XJ 4.0L Engine Hesitates when changing throttle position.

This is getting worse.

Engine hesitates for just a tiny fraction of a second, just long enough to cause the drive train to shudder - an uncomfortable bump.

Often happens about 1/2 second after moving away from a stop under mild acceleration.

Less often when slightly decreasing throttle after steady speed.

New items within last month include: T-stat, plugs, cap, rotor, O2, cat, smog on dyno passed CA no problem. visually inspected vacuum system - Aok.

There seem to be numerous threads about hesitation, but none of them put their finger on what seems to be a common problem that feels like it should have a simple fix.

My old 87 used to do this, and and even when it wasn't doing it, it kind of lurked in the background, but one thing that usually helped was a thorough cleaning and lubing of connectors, especially the ones to the throttle position sensor and that big nasty "C-101" connector on the firewall. It might also be time to check, and even replace the TPS. I found when I replaced and readjusted mine that setting the output voltage too high made the problem worse. You should also do a very thorough check for vacuum leaks, which will also make this problem a little worse.

Matthew Currie said:

My old 87 used to do this, and and even when it wasn't doing it, it kind of lurked in the background, but one thing that usually helped was a thorough cleaning and lubing of connectors, especially the ones to the throttle position sensor and that big nasty "C-101" connector on the firewall. It might also be time to check, and even replace the TPS. I found when I replaced and readjusted mine that setting the output voltage too high made the problem worse. You should also do a very thorough check for vacuum leaks, which will also make this problem a little worse.

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I did everything mentioned above and cleaned the grounds, firewall and dipstick brace. Adjusted the TPS to aorund 14%, which worked well for mine.
Found some corrosion and/or oil in the connectors and grounds, that was messing with my TPS voltages.
There is a TSB, for the early Renix TPS. Seems 1/3 rd throttle is supposed to be the spot, where the TPS acts up the most. Think it was a recall.
I used a conductivity enhancer, a paste applied with a toothpick, into the connectors. Some of the signals sent to the ECU and TCU, are fractions of a volt. Forget the name of the paste, but finally found it, by a model railroad shop, they use it to connect the electrified tracks together.
My old beast is pretty zippy now.
I did the C 101 cleaning on my 87 and promissed myself never again. On my 88 I just jumped and soldered, the questionable wires (any with a line loss across the 101) a couple at a time, eventually I´ll probably have all of them (or most) jumped.