Dash gauges jitter then settle, stubborn starting, occasional stalls

Question

I've done a lot of Googling and been to a mechanic, but no definitive answer on this one yet.

It's a 2003 GMC Savana that runs great, once it's started. It's stubborn to start though, when I turn the key to the on/run position, the dash gauges and warning lights freak out for 5-10 seconds before settling to normal levels. If I try to start it while the gauges are jittering, the engine cranks but does not start. If I wait until the gauges settle, it starts perfectly.

As well, the engine will occasionally just cut out while driving without warning. If I slip it into neutral, turn the key to off, and then restart, it starts immediately.

Battery and starter motor were replaced a few weeks ago, but that did not help.

Given that the dash gauges freak out and settle, I'm 99% sure this is electrical. Maybe a weak ground connection? Possibly a bad ignition switch, though I struggle to see how that would lead to initial gauge craziness that would settle.

Edit:

For the curious, here is a video showing how awful it was at starting before I replaced the ignition switch (thanks dlu!).

https://www.youtube.com/watch?v=hyUpglxfPOQ

Answer 1

The first thing to do is to learn more about what's happening during the initial "freak out." Here are some things to try:

• Working with a helper, listen very carefully as you switch it on and the gauges are freaking out. One possibility is that a relay is having trouble pulling in (which could be either a bad relay or a flaky signal to the relay). You're listening for a clicking sound that is happening, probably somewhat randomly during the freak out. If you hear that try to isolate the source of the sound and let us know what you find.

• See if you can find a way to get access to the wire that is powered in the on/run position of the ignition switch. Getting to the back of the switch may be hard, but if you have a wiring diagram you should be able to find a spot where you can get at it. Then, watch the voltage at that point during the freak out. This will tell you if the ignition switch is the culprit. What you want to see is a steady reading of around 12.6 Volts.

• See if you can find a pattern to the times that it shuts down on the road. Does it correlate with a bump, or switching something on, or signaling, or increasing (or decreasing) engine load – perhaps when something automatic happens like the A/C compressor cutting in or cooling fans starting.