I'm having a strange starting problem with my 2005 V6, and I'm wondering if anyone has ever seen this before.

The basic symptom is: Turn the key, the truck starts to turn over for maybe a quarter of a second, then stops. Stops trying to turn over, just stops. New battery, fully charged, etc.

I took it to a shop. They found something interesting. If they used their OBD scan tool to command the computer to turn on the start relay, then they could start it no problem. And then the truck runs normally - can drive it, no problems, no codes. But without that "energize start relay" command to the computer, it appears the computer almost instantly shuts down the start.

They're suggesting it's likely a computer problem and I should replace it. Seems plausible to me. Any other thoughts?

Thanks.

Are you talking about the "auto start"? like when you turn the key to start it but instead of holding the key to the start position you let go and the car will continue to start itself even though your not holding the key in the start position?

More like "auto stop". When I turn the key, it tries to start the vehicle for about a quarter of a second, then stops.

But, if first the computer is manually commanded (via the OBD port) to turn on the start relay, then it will start.

Sounds like the ignition switch would be a logical place to start troubleshooting since the OBD command presumably bypasses it.

^^^^This was my thoughts as well, ignition switch^^^^

did you check the gas cap?

Thanks for the comments. Ignition switch - yep, we've talked about that one a lot. The shop is quite sure the ignition switch is fine. The ignition switch has been my thought as well. Gas cap? I can check. I always put it on firmly so it would be a surprise to cause the truck to not start? But good idea, I'll check.

At this point the shop has finished going through the Toyota troubleshooting checklist, and a new computer is being ordered.... We shall see what happens.

Thanks.

maf sensor might need a cleaning and throttle body might need a cleaning.

but seems like you guys can try the ignition switch. not sure if you guys can spray electronic contact cleaner and work the key in and out.

Do all gen4 4runners run the starter with the touch of the key until the engine starts or just certain ones? I can do a really quick flick of the key and it will start itself so I assumed all did that. If they do, not sure how it would be the key switch as it just takes a split second for the computer to see it and do it's thing. Unless of course it's losing some other signal like ignition for it to work properly. The computer sounds like it could be the issue but an expensive part to shot gun. I think I'd just wire a momentary switch to the starter.

Yes all 4th Gens have the one touch/turn ignition switch starter system, once you turn the switch to the "start" position the starter stays engaged until the engine fires up, or if the engine fails to start the starter will disengaged after a certain/short time lapse. not sure how long that is for sure though.

Just to bring this thread to a conclusion. The dealer installed a new computer, and voila, weird starting problem problem solved. It returned to starting normally. No more "start, then shut down". Life is good again (except for my bank account!).