Truck Shaking With a Low Idle

Lets give this forum thing another go...

I have a 2003 3.4L Automatic V6 TRD Tacoma with 160K miles. Just when I thought the thing would run forever, I'm having an issue.

Problem: The truck seems to gradually work it's way down to a very low idle (from cold to warm engine temp), the entire cab starts to vibrate, and the AC fan speed lowers. Nothing crazy, but noticeable.

Possible answers: I have read quite a few posts and talked to some motor heads to come up with a few possibilities. Now I'm hoping you guys can help me narrow it down. The most common answers I have received are spark plugs and/or coils, battery, alternator, and idle control valve. There could be others, so don't let this narrow your mind.

Honorable mentions: I replaced the battery today with no change in performance. The positive terminal was extremely corroded before replacement and the CCA's had tested very low. The alternator was also tested and easily put out 13-14V with the high beams and heater fan turned on.

I myself am not what I would consider a "motor head". So please try your best to answer in "motor maintenance for dumbies" terms. If you know the issue, or ways to narrow it down, I want to hear it!

 

If possible loosen the exhaust manifold to exhaust pipe… it sounds like the exhaust is partially plugged.

 

Start with a general tune up:

Sea Foam -> 1/3 a bottle into the gas tank, 1/3 into the crank case, remaining 1/3 bottle through the PCV valve while running.

Drive ~100 miles

Change oil

Replace (or clean if you have reusable) air filter
Clean MAF - with MAF safe cleaner (the MAF is secured with JIS screws, using a regular screw driver will likely result in stripping the screw heads)
Remove intake, throttle body, IAC (JIS screws again), and intake manifold if necessary - clean with EFI safe TB cleaner. The IAC has a whole procedure itself. You'll need new gaskets for the TB, IAC, and intake manifold if you remove them
Replace PCV Valve and vacuum hose - Probably also need a new gromet; be weary not to drop bits and pieces of the gromet into the valve cover- a pick tool or vacuum will be your friend here
Replace spark plugs - the 3.4 requires dual ground electrodes- stick with OEM, NGK/Denso, ignore the "fancy" plugs
Replace wires - Denso or OEM
Replace all vacuum lines - OEM can be expensive... Most people will get silicone lines in bulk online and just send it.
Replace fuel filter

If the low rpm vibration persists, then move on to coils (Denso), and injectors (again Denso, visit MotorWestPerformance and get the "Denso Upgrade" injectors for the 5VZFE). Once you're at this point, I'd also consider a valve cover gasket replacement and valve shim check.