Thread: Bad Gas Mileage and stumbling idle...again

I have searched and found so many threads about this, that I have conflicting opinions about what to do. Heres the problem:
Poor gas mileage
Idle drops down and runs rough when revving the car cold, then pops back up and is fine.
Car stumbles a little at constant low throttle while driving...2500rpm or less. When given more throttle it is fine.
Idle is all over the place within 2-300 rpms when coming to stop or coasting
What I have done:
Cleaned/regrounded MAF
Disconnected /plugged EGR hose
tried two sets plugs...platinum/conventional.

I don't want to start throwing parts at it if I don't have to.
Sooo...
Upstream/Downstream 02 sensor?
TPS? If so...what are the voltage readings in closed and open throttle? (I only have my old B14 Haynes manual)
IACV?
Temp sensor?
Thermostat?
Injectors?
Wires/cap? (I put a new rotor on when I got it this year)
TIA for anyone who can assist

Cleaning the IACV is essentially free, except you should put on a new gasket. You should also check for vacuum leaks, which should be free as well. If you have someone around you that can lend you a known good MAF to test, I would go that route. If your MAF is bad, regrounding/cleaning will not do any good. You can also test the injectors to see if they are firing fine for free.

What solution should I use to clean the IACV?
I have never checked for vacuum leaks before...how do I do that?
Check the injectors for free? Huh?
Pardon me for being naive, the b14 never had any of these issues so I haven't done any of these checks before.

Do you have access to an FSM?
For '94 B13, see EF & EC pg. 37-38, index of trouble diagnosis procedures.

Unstable Idle p.144, Stall when stepping on accelerator momentarily p.163, and Stall after decel p.165 - procedures for all 3 of these symptoms have these steps in common:
- power balance test
- injectors (engine off, key off, should measure 10-14 ohms resistance)
- ignition spark
- fuel pressure
- ecm harness connector
- ecm

Stall when stepping on accelerator momentarily p.163, and Stall after decel p.165, also have the iacv-aac valve in common, as well as ecm power supply and ground circuit.

I used carb cleaner to clean the IACV after I had it off the car and taken apart. One way to check the injectors is to unbolt the fuel rail, tilt it back until the injectors tips are showing, throw some paper towels under them and have someone try to start the car. You'll see if one or more injectors isn't spraying or not spraying well. There are a number of ways to check for vacuum leaks. If you google it you'll find people spraying brake cleaner or something similar around the engine bay while the car is running (but not hot), if you spray a spot and the idle goes up, then you found your leak, but I have not done this so I don't know how safe it is. I built a PVC cap that goes over the intake with a valve stem on it, and then attached a bike pump to it to put pressure on the system and then listened for leaks.

Chk vacuum leaks with, soapy water

Change your spark plugs.....stock NGK....fouled plugs can cause poor gas mileage.

Already tried platinums and coppers

Have you tried just tuning up you engine in general changing your plugs, wires, cap, rotor, fuel filter, air filter? Have you tried premium gas. What size are your wheels, Heavy wheels will also affect your gas mileage. Are you using a modified ECU? Take your car to a reputable auto shop and have a diagnostic done. Is your check engine light on?

You can check the ECU for codes if you like, although Nissan didn't make it easy on our cars. You'll get very familiar with the underside of your dash if you do it.