Intermittent engine hesitation/buck

[ryanfromri]

Hey guys, my name is Ryan and i'm new to the forum. I've looked on here before on how to replace certain parts and you guys are awesome and very helpful! So I have a 5 speed, 2005 base model, fwd Vibe with right around 120K on it. For the past couple of months or so, I've been trying to track down/fix an intermittent engine hesitation. When I start my car up in the morning, it start fine and the first few minutes and few shifts are fine. After that, once the engine is warmed up, it begins bucking/jerking when I upshift through the gears. It is really noticeable when I'm coasting say at 35 mph, and I let off the gas. With both feet off the pedals, my speed obviously decreases but then the engine bucks or hesitates pretty badly. Then, when I let back on the gas there's another hesitation. Also, the engine shakes pretty violently when I come to a stop and let it idle. It idles around 850 rpm, which seems normal I think, but for some reason it feels like there's a lack of power and the engine vibrates a lot. It's gotten to the point where my lower back is killing me from driving it because of the strong vibration coming through and from the random bucks/jerks lol. The lack of power throws off my shifts as well and makes it very difficult to execute nice, smooth shifts. Also, it's weird but it seems like when I rev it really high and shift (drive it like an ahole), the ensuing shifts on my way home are a lot smoother and better. Anyways, I was just wondering if you guys had any suggestions on what to try, I'm not throwing any codes. Here are some things I've tried/replaced already:
New spark plugs, intake manifold gasket, mass air flow sensor (cleaned and replaced), PCV valve, air filter, cleaned throttle body, checked for vacuum leaks under the hood. Also all of my fluids are up/fine, oil changed regularly w/ full synthetic, no leaks.
Basically the only things that I haven't replaced that I can think of are the valve cover gasket (not leaking any oil), fuel injectors, and 02 sensors/exhaust work.
Any help would be appreciated, thanks everyone!

[Caretaker]

you didn't mention new ignition coils. Also, what brand of spark plugs did you put into the car? It is pretty important, although not 100% essential that you stick with Denso products for both. Going cheap on spark and ignition items doesn't seem to work too well in Japanese engines. Every mechanic I have spoken to has said the same thing. My guess is your problem is the ignition coils. Pull them out and you are likely to see some discoloration on the lower shaft. If you feel this is the problem, get some fresh Denso spark plugs and throw them in while you are at it. It won't break the bank and putting new ignition coils on substandard spark plugs is a waste of your time. While failing ignition coils are supposed to throw a code, many Honda owners report just the opposite: no code.

[jolt]

I concur with Caretaker. Also have your battery and alternator tested.

[vibrologist]

I concur with caretaker and jolt.

If their advise does not get your engine running perfectly repeat your search for a vacuum leak but use different methods.

[ryanfromri]

Thanks for the help guys, I'm actually not 100% sure which plugs I put in the car, but i'll pull one when I get home and get right back to you on that. Also, I have not replaced the coil packs, is there a way to test them like say with a multimeter for resistance or anything like that? And yes I believe my battery is pretty old so I could definitely have that and the alternator tested.

[jolt]

Here are the checks per Toyota:

[ryanfromri]

Thanks for that schematic man I appreciate it. I keep forgetting to post back but I ended up replacing all 4 coil packs like someone suggested, and it really helped and smoothed out the acceleration a lot!