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Nissan Nastiness

Car: 1997 Nissan Altima GXE 4cyl, 82K miles

Problem: Occasional rpm drops and stalls at idle, rough running at medium speeds, stumbles. When it stalls it is hard to start. Problem is intermittent but is now happening pretty much on every trip.

If the engine stumbles or runs rough and the accelerator is floored, so rpm goes up to 4 or 5000, the problem goes away. Sometimes it takes doing this a couple of times. Once the problem has ?reset? itself, car will run fine for several minutes. Sometimes the engine will run rough at around 2000 rpm, but flooring it briefly will also temporarily eliminate the problem.

On one occasion while at a fast idle (2000rpm) in the driveway, it started running rough and I noticed an odor from under the car. I think it was the catalytic convertor running hot. Makes me think the engine might be running excessively rich during these stumbles. Also unburned gas sometimes noticed from tailpipe.

I?ve now had this problem for over a year, no obvious connection with time of year, cold/hot, wet/dry, etc. Problem has gotten somewhat worse over time.

So far we?ve tried: Replaced spark plug cables and plugs. Replaced fuel pump relay. Checked for computer codes - none. Replaced distributor. Checked fuel pressure - OK.

I have to ask, What does a hot catalytic converter smell like? Also, how can you tell it is unburned gas coming out your tailpipe and not water?

I think it’s moments of running rich, also. Put fuel injector cleaner in the gas tank. The fuel injectors may be sticking.
Use an MAF (Mass Air Flow) Sensor cleaner, and Throttle Body cleaner on the iac (idle air control) valve, and inside the throttle body bore.

Hot catalytic convertor? Well, just the smell of hot metal - and maybe some nearby insulation - that I haven’t noticed before. Unburned gas? Not dribbling out, just an odor from the tailpipe that indicates a higher level of unburned hydrocarbons.

hmm interesting. My 1990 maxima 5 speed manual was running real rough, making some smell (you could smell a gas-like smell), revving unevenly (tach would shudder a bit at lower rpm), and had considerable power loss. We took it to a grismer and one fuel injector was totally dead (I’d been driving it as a 5 cylinder I guess) and they said all the others were operating way out of spec. You sound like your having the same kind of problem and with all the stuff you tried there aren’t many other reasons it could be happening. The shop wants to charge 2300 all told (1200 for 6 injectors) so I hope it is something else. it could be a fuel filter but I doubt it.