QuestionI've a 95 Tacoma extended cab 4x4 3.4L V6 Automatic 146K miles that's driving me nuts. Driveability is very poor, acceleration slow, and gas mileage dropped from "normal" 16mpg to about 9 or less. It sat for a few months in high humidity at 4000ft elevation, had dead battery. Charged battery and it usually starts and drives, but has a horrible "bog" or pause on initial acceleration. Same warm as cold. Engine seems to warm up normally to just under mid scale in a few minutes (about a quarter mile of residential street). Throttle response is terrible. Bogs when you crack the throttle, even in neutral sitting still. Pull onto highway, floor it, and it will pick up, though very slowly until it revs to 2300 or 2500RPM. Still climbs slower than it used to but the big thing is the low speed bogging. Since problem occurred, have changed plugs (dual electrode Bosch, gapped properly) Plug wires, Cleaned then replaced MAF, air and fuel filters, cleaned throttle body, checked grounds (added extra grounds from battery to block, intake and firewall). All voltages on the ECU are within specs except a couple that are max 14 volts show as 14.3 volts. Throttle Position sensor looks good, can't find any flat spots (with resistance check while disconnected, or voltage check while running). Idle seems normal speed, no apparent missing, about 1200rpm cold, 750 warm. This morning, fired it up (takes about 3-5 seconds cranking to start) and it was more sluggish than usual. Put it in gear and it instantly died. Took over 30 seconds of cranking to start again and was rough but even (like every other plug firing, but not like a harley) Crank 5 or 10 seconds, let go of key (hear fuel pump run for a second) repeat. Eventually fired up, but even floored it took a few seconds to clear. If this were a carbureted car, I'd swear the accelerator pump wasn't working, at least for the bog when you crack the throttle. Not so sure for the hard restart. Driving on level ground, can sense a slight surging (rpm variation) but can't see it on the tach. The truck is typically driven about 5 miles one way to work and back. Drove it into town a few weeks ago (30 miles mostly downhill to sea level) and it didn't show any codes with a generic OBD-II tester at the local Checker store. The bogging isn't as bad once the truck is warm (after 5 miles of driving in the morning, or a mile in the afternoon). Morning air temp here is perhaps 45 degrees F., afternoon about 70F, so we aren't seeing freezing cold. Even in the afternoon/evening, after warming up a bit, the bog is still there, not as bad as morning, but driveability is still very poor. Part throttle doesn't have too much effect. To accelerate, you really need to be at 3/4 throttle or better, and there's a big lag between throttle opening and response. No dash light, no codes when I checked it. Thinking of changing the temp sensor and thermostat next, then Oxy sensors, but really don't want to just throw parts at it. Haven't put timing light on it yet (moved recently, can't find it, no mechanic friends) or scoped the Oxy Sensors. Perhaps drag the oscilloscope out this weekend and look at the Oxy Sensors. Any ideas?? If I had the cash, I'd be tempted to buy a new(er) one or at least throw parts at it, but cash flow is not wonderful right now.
Thanks
AnswerI don't think there is a problem with the O2 sensor it sounds more like the timing may be off, if the timing is off then I would inspect the timing belt next to see if it jumped on the pulleys by removing the top part of the plastic cover on front of the engine, another possibility is a loss of fuel pressure, monitor the fuel pressure while driving with a gauge hooked up, one more thought, the catalityc converter could be plugged up , so there are a few things you should check out, let me know if any of those solved the problem.
