I'm not trying to tell you what bandwidth, or sampling rate, analog/digital/usb, storage type, scope maker or seller to pick. I don't know if this is a one-time buy for a one-time use or if later on you want to delve into the deeper workings of the digital automotive controls.
Just don't be fooled into thinking a 250MHz scope is overkill unless you're into Ham radio.
The excerpt below was written for college EE students at KU and is an excellent quick overview of the subject of bandwidth, which is how scopes are advertised, and rise times, which is what you see. If you don't want to read the whole PDF, look over the excerpt below which shows how your equipment determines what you see.
Rise time Vs. Signal Bandwidth
t
r=3.5/f-3db
"One very useful application of this equation is when using an oscilloscope. The risetime
observed on the display will be a combination of the risetimes of the signals being
measured, the oscilloscope probe, and the oscilloscope as given by:
trise≈ Sqrt [ trise (scope)2 +trise (probe)2+ trise (signal)2 ]
To examine the influence of each of these quantities, let’s look at a digital system. The
question to be answered is “When does digital become analog?” Is it for a 1 MHz clock, 10
MHz clock, or 100 MHz clock? In reality, clock speed is less important than rise time!
Modern logic families have risetimes on the order of 1 ns. This yields a signal bandwidth of
Assume that a 50.0 MHz oscilloscope and a 10.0 MHz probe are available for making this
measurement. The risetime observed on the display will be closer to 1.55 ns, a ~50% error.
For this reason, it is very useful to compute the best-case risetime for the scope/probe
combination you are using and keep this in mind as you are making measurements. If the
risetime of the signal you are viewing approaches the best-case value, your scope is limiting
the measurement and there may be features in the signal that are hidden from you."
The best advice I can give you having spent five years in oil field data transmission R&D is to match your needs to the capability of the equipment you buy. You're better off borrowing or leasing good stuff than buying cheap.