88 = 1 o2 in the header.
My biggest mileage gains came from a ho header swap with a custom made 2.5" down pipe. Our renix rigs have a log style manifold, the how got a tubular manifold..it's a header basically. The 2.5" down pipe helped sound and power, noticeably.
Relocated your iat sensor..free of charge and few minutes of your time. Intake manifold heat shield for around 12 bucks. I have a 60mm throttle body and it feels great, but saw no power gain at all. If it helped or hurt mileage it wouldn't of been enough to notice on paper..so that be a last resort type of mod for me again..
703s or 700s or 710s will help you out..19-20lbs between the all, helped idle ALOT. also no more stumbling when crawling off idle slowly..I've got a 5speed, so. Slipping clutch with no gas it would almost die before, now it holds strong. These were done after the header/down pipe and on paper I saw no gain, but I also went from falken all terrains to some nasty mud terrains within days of this mod. I lost no mileage with the MUDs, which means I would of probably gain 1mpg or so had I kept the AT's. the mudders took any gain they gave me.
Fwiw, mines a 87 xj, ax15, 231, 3.55s, 31s and about every single bolt on you'd imagine, but also done CHEAP, or when needed..header cracked, I grabbed a APN for a ho and got a custo, down pipe with a flew section added..no more cracked header
Injectors were yanked and cleaned/rebuild by myself. Did a lot of stuff to help keep the exhaust hot and intake cool. 2 cans of vht 3000* ceramic paint..about 7 bucks a can. Coated, heated in oven for 1hr at 200*, let cool, recoat & bake at 300* for 1h, let cool, repeat at 400* and repeated at broil or 500* except I went 2hrs at that temp. It's didn't flake, I knocked on it with a ratchet will removing other parts, no chips. Stayed stronger. I later replaced the gasket and wrapped the header, 13 months or so later. Stayed strong!
I could get my hand close to it. Without it being to hot, while the uncoated stock log manifold would bake your hand within a few inches.
The heat shield is actually a foil type stuff from summit. Sticky on one side, shiny on the other. Dropped intake manifold enough to place hand on the manifold. Before you would be burned after a few seconds.
I'm also running a 2.5" flowrasper with a 100 cell magnaflow cat. Dumped after the axle.
I'm getting 17mpg city and 21highway. Pushing the 350k range on the original motor. Doesn't look to have been rebuilt but who knows. It actually just started knocking/rattling. So russ has started on a stroker. Even still she holds 21psi at warm idle & has decent compression, cyl 6 being a wee bit low..mph is with .2mph of my gps which can't get any closer, and I'm hand calculating. I can pull more if I draft on he highway I'm sure. It drops to around 14/18 if I'm driving hard. I run 65-70 normally.