I have a 2017 4runner limited. Has 32000 kilometres (19900 miles). Took it in for its's 3rd oil change and was told upon dropping it off it is up for it's 3rd scheduled maintenance which will include the following:

- Check installation of driver's floor mat.
- Reset Maintenance Reminder Light or system.
- Inspect all lights and horn for proper operation.
- Inspect wiper blades, linkage and washers for proper operation. 1
- Visually inspect drive belts adjust tension if required.
- Replace engine oil & filter (synthetic).
- Lubricate locks, latches and hinges.
- Inspect and adjust level - engine oil, brake fluid, engine coolant, power steering fluid, transmission fluid, differential fluid, and washer fluid.
- Remove & inspect engine air filter. 2
- Remove wheels & visually inspect brake pads, calipers, rotors, brake lines and hoses.
- Remove brake calipers and/or brake drums. Inspect and measure brake rotors, drums, pads and shoes.
- Check and record tire tread depth. Examine tires for damage and uneven wear.
- Rotate tires (applicable to same size wheels, front & rear) or alternatively perform seasonal tire change-over. 3
- Perform 12 Volt battery service and comprehensive electrical charging system evaluation.
- Inspect valve clearance (audibly).
- Check steering gear, linkage and shock absorbers for looseness, damage or leakage.
- Inspect ball joints and dust covers, driveshafts, chassis nuts & bolts for looseness or damage.
- Inspect fuel system for leaks or damage, inspect condition of fuel tank band, fuel tank cap gasket, fuel tank vapour vent system hoses, fuel lines and connections.
- Inspect engine oil cooler lines and automatic transmission cooler lines if equipped for leakage, looseness or damage.
- Inspect exhaust system for leaks, damage or broken hangers.
- Record inspection results, measurements and component condition on inspection form and/or repair order.
- Remove & inspect cabin air filter.

Upon picking it up and starting, the idle is off. Feels like a mild shake throughout the vehicle. Problem is, it is not consistent. Rougher at start than other times. Do not notice it while driving, but at every light, there is a 50/50 it is noticeable. In neutral, I rev the engine a bit and once it revs down, sometimes the rough idle is there and sometimes it is not.

I few days later, this is really bothering me so I start looking at the service paper from the dealer with the full list of everything that was checked on the vehicle and cannot make heads or tails of what may be causing this. I pop the hood, and see both battery terminals have some blue stuff covering them, but do not think anything of it.

Again, a few days later (today), I pop the hood and for some reason, no idea what lead me to it, but I reach over to the positive battery terminal and give them a wiggle, solid. I grab the negative battery terminal and it is very loose, taking 12 or so turns on the ratchet to tighten it properly.

I fire up the vehicle and it seems the rough idle is gone. Take it for a short drive and it seems to run like it did prior to the service. Is this a normal symptom for a loose negative battery terminal, to cause the rough idle?

I will be able to drive the vehicle more tomorrow, and will see if it is really gone.

Thoughts?