2005 chevy suburban, in Canada, bought grooved throttle body from Ron, was at 17.7 L per 100 km when I started, gas consumption went to about 18.8.... yes it has more power... Ron suggested that i do a few things, gap the plugs which i did, the dealer says they should be gapped at 45 thousandths, the ngk double platinum plugs i bought two months before came pre gapped at 40 thousandths, i plugged in a spareplug and couldn't see any difference all the way up to 90 thousandths.... seemed outrageous to me, but tried it, runs totally awesome and accelerates better...... Also capped the pcv valve.... removed the intake and replaced the gasket, did the knock sensors and wires, cause I was there.... changed the exhaust manifolds and gaskets, a couple studs were broken, so dealt with that. Actually wrapped the manifolds with that exhaust wrap too.... 6 months before this I installed a new magnaflow y pipe, tail pipe and muffler, oxygen sensors, plugs, wires, even cleaned the throttle body with seafoam spray and seafoam tank additive..... plus replaced the power steering pump, belt tensioner, had a high pitched wine that drove me nuts for a while, but none of this improved the mileage here either..... then I tried the volo computer tuning chip, mileage stayed around 18.8, after 6 months or so I decided to remove that, and now today oct 4, 2019 it's at 17.8 L per 100 km.... working it out with liters and kms, puts it between 18 to 20 L per 100 km, which is really where it's been since the start.....eccept once in a while it spikes to 22.... not sure why. Hopefully I haven't missed anything.
Last point, i also have a 2002 Chevy astro van, almost identical results, with same mods... except I did wrap its y pipe with exhaust wrap.
Then I bought a small car, to save gas money, right. Just another expense!
I said to my son the other day, Canada's government has it all wrong, trying to get us to convert to electric cars, all we need to do is correct what we currently have, so they are more efficient!
Help is good, I definitely gave up for a while... I don't know what else to do... I believe there is a solution, that's why I am posting this comment. Thanks! Steve