My Q45, 1993 model with 109.000 kilometers. has for the last 3 years had an intermittant problem with rough idle and missing with black smoke blowing. It runs OK for monts on end then suddenly it starts for a day or two.

To try to fix the problem the Meter ASSY-AIR flowmeter, Coolant temperature sensor and Knock sensor has been replaced. Car has been serviced by Nissan in Sydney since new according to service manual.

As there are very few Q45 in Australia, help is hard to find.

Desperate.

Read a round on intake path cleaning. How's the IAC, EGR and PCV valves and their connections? I presuem you don't have the precats on the headers?

We love to here from down under, so read the posts by Q45tech especially for a good grounding.

Welcome to NICO!

I would consider replacing the spark plugs, make sure you get the real NGK's. I experienced similar problems when I had bad plugs, though my cats were taking care of most of the excess fuel. Also consider the the plenum/TB cleaning as mentioned above.

Good Luck!

Could be leaking valve covers. Oil on the spark plug will cause that intermittant missfire.

red

Be sure to clean the throttle body (TB) well. This is the butterfly on the end of the aluminum plenum. Take off the black plastic intake pipe and clean it thoroughly.

DO NOT USE CARB CLEANER!!!!!! It will eat up the plenum coating. Only use throttlebody cleaner.

Make sure the Idle Air Control (IAC)passage is not blocked. This is the little hole that bypasses the butterfly. It allows air into the engine, for idling. Use the TB cleaning fluid on it. You should use most if not all of the spray can of TB cleaner.

The dirty throttle body and IAC passage causes the poor idle control.

The Mass Airlfow Sensor (right after the filter) causes the black smoke and poor gas mileage.

It can be cleaned with break cleaner (brake cleaner does not leave a residue, like TB cleaner). Make sure the connectors are clean, then put some di-electric grease on the connectors. Be very careful not to break the connectors when removing. The little metal spring clip needs to be pried apart, to remove the connector. Use a small screwdriver to pry the wire apart. Do not remove it, just release tension, so you can pull the connector off. It clicks back on easily. While you are at it, clean the black plastic pipe, and make sure the other hoses are in good shape and make good seals. a vacuum leak will cause all kinds of problems.

The plugs are an important part of the picture, as well. A lot of shops don't use the NGK plugs, and this will eventually be a problem. I had to get rid of 2 sets of Bosch plugs on my cars, before I realized the NGK are the way to go. Wes used to sell thease at a great price.

Go haead and replace the fuel filter, while you are at it.