2500 RPM stumble partial throttle 2.0 -4 Options

[SVG223]

2400-2600 rpm stumble with partial throttle, stumble goes away under full throttle. Runs smooth at all other RPMs. Pulled the plugs, a little lean maybe?



Edit 3-17-25 I found a possible cause; worn distributor bushings causing a variation in the points gap.

[emerygt350]

That is looking very lean as well. Is this stock? Have you checked the resistance on the CHT? Has your MPS been played with?

My new tps board went bad in less than a year and resulted in that stumble, however, I think you may be asking for other problems if you don't richen that up a hair.

When the TPS develops a wear issue I found that the 'whole' thing shuts down, not just a miss on a cylinder, the computer basically tells all injectors to stop firing. Strange considering the job of the TPS (accelerator pump) but that is what I found.

[SVG223]

That is looking very lean as well. Is this stock? Have you checked the resistance on the CHT? Has your MPS been played with?

My new tps board went bad in less than a year and resulted in that stumble, however, I think you may be asking for other problems if you don't richen that up a hair.

When the TPS develops a wear issue I found that the 'whole' thing shuts down, not just a miss on a cylinder, the computer basically tells all injectors to stop firing. Strange considering the job of the TPS (accelerator pump) but that is what I found.

I had these plugs under a strong LED shop light which may have made them look more white.
It is stock. I just pulled the MPS off and was eye-balling the seal. I have heard of inserting a potentiometer in the circuit to tune, which sounds interesting.
I adjusted the fuel pressure from 27 to 34 psi to see if the miss would go away but it didn't. The car did seem to run a bit stronger at 34 psi or it was just later in the day when the air was cooler.
This engine may have been rebuilt. I'm wondering if resistance should be added to the mps after a slight increase in displacement. More to read. I think no.