gas mileage question

This may end up being a repeat post, as the first did not seem to go through.

I recently changed the air filter and plugs (Bosch Platinum 4+). Did the front plugs first, the back ones were done a week later. With the fronts done I noticed an immediate and marked improvement in gas mileage and power. However, when I did the rear plugs – and also the wires after tearing one off – the gas mileage is back to where it was, maybe even a bit worse.

Any insight as to why this would be? I had to disconnect the battery for the rear plugs, which would cause the PCM to lose any data, but that is supposed to reprogram itself. Haven’t checked the O2 sensor or other items (not sure what I’d be looking for, off hand), but it would be quite coincidental for them to go wrong in between doing the front plugs and the rear ones.

Other info:
o 105,000 Km
o gas mileage is particularly bad until the engine fully warms up (about 90% of the way through my daily commute)
o OBD code P1404 – EGR valve closed pintle position. This comes up just occasionally.

Does this EGR situation indicate something especially relevant to the gas usage?

What other things should I look at for bringing the gas mileage up? Is there something that can be done to reprogram the PCM more effectively? Any comments, opinions or ideas are welcome, and any specific knowledge would be wonderful. Thanks in advance.

Are we talking a +/- 5 MPH difference from when you just did your front plugs to what it is now? My guess is that the mileage changed, you wanted it to because of the plugs, so you associated the two together.

Mileage depends on a bunch of different factors. Plugs can make some difference, but gas quality, weather, driving conditions, lead foot, etc all play a part. I wouldn't put too much stock in changing the plugs made a significant difference in this case.

About 4 mpg (you did mean mpg, didn't you?)difference (less) once the back plugs were done. It could be just imagination at work. I try to drive consistently, and I buy my gas from the same chain. Still, there are a lot of variables in themix.

Just wondering what kinda mileage you're getting? I consistently get about 22MPG. My driving is about 60% highway/40% city

You know I have 85000 miles on my Venture and I consider it a great vehicle....I sell Honda's and the Venture rides and performs better than the Honda Van..as for mileage...my wife was following me in a U Haul truck last summer...and I was going an average of 45 mph...she got over 36 Miles per gallon...I find at speeds of around 75 on the interstate I average 25 mpg...when I drop it to 65, I get around 27...mostly driving with cruise control...when I haul my Aliner Trailer (1250) lbs, I get around 18 mpg at 75mph and around 23 at the 65 mpg range...so the weight of the foot is directly proportional to the gas mileage...I have changed the transmission fluid at 60000 miles and plan to have the Dex Cool changed soon too...I was told that the reason for the Dex Cool is because of dis similar metals in the construction of the engine and Dex Cool helps prevent corrosion due to electrolysis...I check my radiator frequently and there is no corrosion to be seen....it runs rather consistant temps unless coming out of Nevada into the mountains at 75 mph at an ambient temp of around 105 then it tends to rise on the temp gauge around 25 percent then when I get on level, it drops back where it normally rides...I always change the surpentine fan belt at 60000 miles, the indoor AC filter at 60000 miles, the air cleaner every 24000 miles and that is all the maintenance I really do...Oil and filter every 3000 miles religiously...so far so good...I would buy another one...I always get a "program car" from a GM dealer.