I have a 1996 V6 4Rnr Limited. While driving on highway with slight upslope and into a headwind, I started to slowdown unintentionally and thought - what a headwind. But then the rpm was also dropping almost to idle. Got off to the side and an off ramp while pumping the gas pedal. Vehicle never died but had no power above idle, but every once in a while the engine would catch and surge ahead only to again drop to no power. I stopped but kept pumping and eventually the engine/rpm came back to normal and I drove 75 miles home with no other problems. I had just gotten gas and thought maybe I had bad gas. Had no additional problems for several weeks. Then one day, I pulled out in front of a fast oncoming truck and floored it to match his speed and at high rpm and slight upgrade it again lost power and dropped to idle, but this time it eventually died. It started right up, but took some pumping to get the engine to again run above idle and normally. Again, several weeks went by with no problems. Then it began to die at slow speed, would not get above idle without pumping it a lot, but would again begin to run normal. That was several weeks ago. Does this sound like a fuel pump issue, a fuel filter issue or ?? Don't want to just start replacing parts. Any thoughts?

 

Are there any stored pending error codes? I assume you would have mentioned a lit CEL.

Unfortunately, Toyota didn't provide a testing port on the fuel system, so it's not very easy to test fuel pressure.

From the description, it certainly sounds like a fuel supply issue could be a likely cause. Could also be some issue with the MAF, fuel pressure regulator, possibly even the ignition. Probably not a clogged cat because it likely wouldn't 'recover' after failing.

 

CEL never lit up. These intermittent problems can make a guy lose his hair

 

Any other ideas?

 

Pending codes are codes that the computer catches, but which don't light the CEL. Might be a clue.

Other possibilities:
- torn/leaking intake between the MAF and throttle body
- failing FPR (pressure too low, pressure too high, or leaking via the pressure reference line into the intake)
- dirty or damaged MAF (although that's unlikely to fix itself)
- Contaminated gas that you're slowly working your way through

It's hard to diagnose from afar with just some generalized symptoms. Can you get an OBD scanner smartphone gadget and see if the O2 sensor thinks it's lean or rich when this is happening?

 

Jomoka,
Thanks for the input. Am awaiting the arrival of an OBD II scanner to see if there are any codes that didn't lite up the CEL. I wondered about the contaminated gas since it fires occurred a short time after I filled up at a station I had never been to before -- even though it was an Exxon station. I've run 3.5 tanks through since then though so kinda discounted that idea. Could still be the problem though. Bought a new fuel filter to install this week. Plan to cut the old apart and see what it looks like inside. Checked the intake and don't see any tears and seems to fit pretty well. Will try to check the FPR. Thanks for the input.

 

What do the plugs look like? If it's running poorly, they could be a clue as to it being too rich or too lean/

 

Certainly sounds like a bad fuel pump or clogged fuel system. The fuel filter is a cheap and relatively easy replacement item. Easy to access but sometime the connections can be rusted together. If the fuel pump stops completely you can try banging on the gas tank with a rubber mallet. Sometime the pressure spike from the impacts will get the pump working again temporarily.