"Robert Coffey" > wrote in message
news:ghEme.9935$3u3.9116@trnddc07...
> I just bought my first jeep! a 98 4.0 tj. when the engine warms up it
> "hiccups" at idle or when running at low rpm not under load. 81k miles,
> new air filter, spark plugs, plug wires look good. any suggestions?
>

Did it do this before the tune-up? We need to know whether
something in the tune-up did this, or not.

Might be time for an O2 sensor (or two...).

Have you checked the plug wires with an
ohmmeter? How's the cap and rotor?
Vacuum advance working? Timing set?
No vacuum leaks?

You can use a timing light on each plug
wire to see whether the 'hiccup' coincides
with a certain cylinder spark drop...
three things, fuel, air, spark... one is
missing, could be fuel (sticky injector)
or spark (bad plug (it's happened!) or
cable, rotor, cap). Normally you'd feel
a bad position (crank,cam) sensor under
load as well as no load... you can check
your TPS (throttle position sensor) easily...
get yourself a Haynes, Chilton or (best!)
factory manual. Good luck.
__
Steve
..