1997 Altima engine issues...

[DSPDA3]

Lately the Altima has been running rough; i.e. hesitation, missing at idle and throughout RPM range, spewing black smoke, in addition to consuming a very large amount of fuel. I think I'm averaging less than 20mpg. I've changed/serviced the following items...

Air filter
Fuel filter
Fuel system cleaner
Spark plugs
Plug wires
Distributor cap
Rotor button
Fuel system cleaner (again)
O2 sensors
Fuel pressure regulator
Spark plugs (again)
Intake manifold gasket (blown)
Spark plugs (third time)

I had NRV Nissan change out the manifold gasket and plugs for the third time, and it was running like a champ last night and this morning. After about 30-35 miles on the new set of plugs, the original symptoms returned. I spoke to the service rep at the dealer, and they told me they had tried a used MAF sensor but it did not change anything. They put in new plugs, and it smoothed out, at least until this morning.

Any thoughts as what else to look for? Would a bad EGR valve cause the same symptoms?

[SierraFox]

ECU?

[Scott]

MAF sensor?

[DSP33]

I was having very similiar issues on Sarah's Volvo wagon. It turned out to be a bad ground and a couple of other broken wires or solder failures. This stuff is really tough to diagnose. The guys that worked on her car probably spent 4-5 days finding these problems. I would have given up...

[DSPDA3]

An electrical problem is what I'm leaning towards. Julie works with another vet whose husband is a mechanic. I took it by his place, and he hooked it up to his diagnostic machine, and it came back a few tests not being complete. We pulled the connector on the MAF, and it continued to idle without stalling. I did the same thing the day before, and the car immediately stalled out. Perhaps the computer is running the show, in a pre-set mode from the factory, and not relying on real-time engine data to adjust the A/F ratios, etc.

[mrtwo]

Just a shot in the dark, but has anyone checked the coolant temperature sensor? If the sensor is bad the engine can run rich. I don't know a reliable way to check the sensor, but they are usually only $20-30 each.

PS: your car may have two temperature sensors - one sensor for engine temperature feedback and another sensor to run your temperature gage. You want to replace the one used for engine temperature feedback.

Good luck.

Tim R

[DSPDA3]

I don't think it's been checked. I'll look into it. Thanks for the heads up.