I have a 1994 Nissan Altima that recently starting to have a rough idle when in drive?

Question

I was driving home yesturday and when I let go of the gas and the car sits in drive at a red light the RPMs lower a little bit and the engine feels jittery almost like it's misfiring or somthing. When I give it gas I don't feel this anymore. It is less apparent at Park. Before I open the hood I want to see what others say. The best answer get's 10 pts.

Answer 1

There could be lots of reasons for a rough and low idle but one of the cheapest to check and fix is leaking vacuum. An engine develops vacuum as it runs and a leak in an engine's vacuum system will definitely cause a rough idle. The engine will otherwise run fine at highway speeds.

To check for a vacuum leak, lift the hood and listen for a hissing sound from the leak. Run your fingers along rubber hoses to see if you can find the leak by touch. (If you are not familiar with things under the hood, you probably shouldn't touch anything, however!)

Another possibility for a rough idle is a bad oxygen sensor. This will almost always be associated with a dropoff in gas mileage -- where you used to get 28 mpg, now you get 20, or something like that. Again, the engine will seem to run normally at highway speeds.

There could be many other possibilities but these are two of the most common.

Answer 2

There are a variety of conditions that can cause low idle,
the most common is low fuel pressure because the fuel filter hasn't been changed out in ages.

When was the last time you changed your fuel filter?

Other typical scenairos for modern cars are.
Fuel pump is worn down and not delivering enough pressure,
Fuel pressure regulator is not working properly,
Fuel injectors are clogged.
Try a few bottles of fuel injector cleaner down the gas tank to reduce varnish build up and clean the injectors.

You may have need for a tune up if your spark plugs are worn. When was the last time you did a tune up on the vehicle, including wires?

These are the cheap things to try. There are other causes for low idle that can get very expensive, but I'd go after the most common causes first.

Answer 3

I would try basic tune up first and some cleaning.

ck air filter - replace if dirty.
Clean throttle body.
Change spark plugs and wires.
Change fuel filter especially with ethanol.

let us know after these things are done.