[lilstang]

My stang has 165,000 miles on it. When I'm driving on the Highway the RPM jumps up and down but the engine does not change in its sound. Then it goes back to normal. Also the check engine light comes on but it is intermitting. I also notice the acceleration is slower. When it is in park it will jump also then the check engine light comes on. It started when it weather was getting cold. TPS was change a few years back. I having work on it yet. I tried to use fuel injection cleaner but still the same issue w/the RMP and check engine light

[C J]

have you pulled the codes?? if so, what are they??

[sleeper_inc]

I'm guessing either your ignition modual is dying, or you have a loose connection somewhere

[Green Ghost]

this might sound funny but you might want to check your alternator silanode ( i think i spelled it right) mine would do that but then shut off

if i remeber right my rpm would just up then run funny

[giamanut]

If when it jumps it goes to about half scale. then one of your coils are failing car will read half scale with a failed coil