Miata bucking in hot weather

[maureen]

I have a 91 miata and when driving on hwy at 60mph after about 30 minutes the rpm starts to jump from 2 to 3
there's no engine light
i changed the plugs and wires, gas filter and still the same
when it starts jerking or bucking the rpm jumps but the speedometer stays at 60mps
Anyone has an idea what it could be

[riefdaddy]

My first inclination is to check your grounds and ensure they are nice and clean. If you have an intermittent ground issue, it can effect your coil packs.

[wannafbody]

Could be a bad ignitor.

[maharaj]

Don't worry, Kung Fu Jesus will be here shortly with the answer. :bow:

[kung fu jesus]

After seeing what Tony (Demon I Am) went through, I would lean towards a fuel pump or fuel pump relay.

The fuel system will throw codes when it is emissions-related, but not for much else.

The other possibility may be a failing coil pack. The jumping RPMs points to that. May I presume the RPMs jump independently of the actual engine speed? Ignitor is also a possibility. These early NAs rarely throw ignition codes outside of a bad CAS.