Idle Fuel Mileage Issues

[lstevens76]

Ok, so if you've read my build thread you know I replaced every gasket/o-ring on the block recently (just over 500 miles ago) along with head gaskets, heads were milled, new valve stem seals, cam seals, timing components, water pump, radiator, etc....

 

I just finished my first "full" tank of gas so I could get a read on the mileage and I'm at 18/19.  Considering over 1/2 of my driving is 13 mile trips that are over 70% interstate I am fairly certain I should be getting at least 23/24.  

 

I'm fairly certain this issue is related to another problem I'm having that isn't setting off a CEL Code.  I have odd idle variations.  It doesn't "fluctuate" but will the idle speed will change, then remain there for a drive or two, then change again.

 

Example:  One trip the idle will be at 750 and remain there whether the AC is on or off.  Another trip it might be at 950 w/ the AC on but 750 with it off.  Next trip it might be at 750 w/ the AC on and then 600/650 with the AC Off.

 

The only code in the system is a P0441 (Purge Flow Incorrect) which I believe is related to a failing purge solenoid (I previously had a P0443 before all the engine work and was hoping it was vacuum lines which were replaced).

 

I did not clean the IACV, which is on my list to do this week or weekend.  What else could be causing this fluctuation?

 

To note:

New Gaskets/reseal (as mentioned above)

New Plug Wires (NGK)

New Spark Plugs (NGK Irridium)

New PCV (about 500 miles or less before the engine pull, but I have a new one as well)

New Radiator

New Air Filter

New Fuel Filter

New Timing Components, Belt, Idlers, Tensioner, and Water Pump

Most vacuum lines replaced (a few left I could replace)

New Separator plate

New PCV Hose and T from the Block.

 

The 0441 was transpiring prior to all this work and the 0443 was prior to the work and has not reoccurred yet.    

 

The AC Radiator fan is not currently plugged in, I do have a replacement for it.  I do have an issue w/ the AC not working at an idle which I believe is related to this fan, but I don't see that causing a problem with the idle itself (I could be wrong and I have a fan I intend to put in shortly).

 

Temperature gauge sittings perfect (doesn't fluctuate)

 

I am leaking no fluids 

 

Running Castrol Edge Synthetic w/ a Bosch Filter and no leaks.

 

Start throwing ideas please.

[1 Lucky Texan]

hmmm....I'm gonna throw out Engine Temp Sesnor or its wiring/connection. maybe the ECU sometimes thinks the engine is cold and is boosting fuel ('choke' mode)

 

 

Might not hurt to throw a vacuum gauge on there. Some parts stores will loan them out. If they don't have a chart of symptoms, you can find that info online easily.

[Fairtax4me]

If you have a code for purge flow and a previous code for the evap system put the ECU in test mode and make sure

1. The purge solenoid clicks on/off

2. Air should flow then stop in correlation with the valve clicking on/off. If air flows through the valve all the time that is a constant vacuum leak. This will change your idle A/F mixture depending on outside air temp as fuel in the tank evaporates and is drawn into the intake manifold.

Edited June 2, 2015 by Fairtax4me

[86 Wonder Wedge]

Why the NGK Iridiums (Iridium IX, I assume)?

 

OE is either V-Powers or Laser Platinums (depending on the year). The EJ25 is VERY picky when it comes to plugs and its waste spark ignition.

 

Aside from that, if you rev the engine and then snap-close the throttle, does it return to idle quickly or sort of float its way down? That can point you toward a vacuum leak.

[lstevens76]

Why the NGK Iridiums (Iridium IX, I assume)?

 

OE is either V-Powers or Laser Platinums (depending on the year). The EJ25 is VERY picky when it comes to plugs and its waste spark ignition.

 

Aside from that, if you rev the engine and then snap-close the throttle, does it return to idle quickly or sort of float its way down? That can point you toward a vacuum leak.

 

First, it's an EJ22E not an EJ25 ('96 OBS).  Haven't tried that yet.  Per torque while driving the vacuum fluctuates (as it should with acceleration) from 5 to 25 inHG.  It doesn't fluctuate at an idle and holds pretty much around 23 inHG per the OBD system.  

 

The Irridiums were price.  They were only a few dollars more than the NGK Coppers and cheaper than the lasers on Amazon when I purchased them.

 

It does run well and has good power.

 

If you have a code for purge flow and a previous code for the evap system put the ECU in test mode and make sure

1. The purge solenoid clicks on/off

2. Air should flow then stop in correlation with the valve clicking on/off. If air flows through the valve all the time that is a constant vacuum leak. This will change your idle A/F mixture depending on outside air temp as fuel in the tank evaporates and is drawn into the intake manifold.

 

I kept thinking it might be something like that but every post I read about it people were saying ignore it and it doesn't cause problems (that wasn't my intention though).  It also makes a lot of sense that the idle seems to variate by temperature (which was baffling me and didn't make sense so I didn't post it).  

[86 Wonder Wedge]

Ah, I thought it was a 25D (got my cars mixed up). And as odd as it may sound, I've seen issues with some waste-spark ignitions using non-OE plugs (like iridium over copper or platinum over iridium) with issues at idle. My experience has been than the cars simply have a hard time with iridium under a low/no load condition. But, long term will tell.

 

As for a potential vacuum leak, I agree. The purge could be stuck open allowing "unmetered" air sneaking in. Do you also have the actual MAF voltages on your scanner or just the converted units?