longhungsilver

I know everyone has done a mileage thread before so i thought wut the heck ill ask the experts what they think of my particular situation..

I have an 89 4runner with 291xxxkms on it.. its a 22re. ive recently changed all the fluids, timing chain (and all parts that go along with it), adjusted the valves, adjusted the tps ( was having rough idling, still not perfect).. cleaned out the throttle body, new cap, rotor, plugs and wires (ngk)... recharged the k&n air filtre it came with...adjusted tire pressure etc etc... Its running on 31s BFGs..

Anyways on about 50litres of my 60 or so litre tank i average about 300kms! to me that seems terrible... even back in the day with my 89 mustang i got 350kms to 50litres!

Any ideas on what the possible culprits are? The old spark plugs came out pefect so the engines not running rich... I suppose my tps could be fudging me out of sum gas mileage but how much?? the idle isnt strong it moves around 800 give or take 100rpm... its not terrible either.. and sumtimes when i stop its almost pefect and other times its not.. and ever now and then it revs up then dies down revs then dies ... then i drive to the next stop light and its fine....

But thats more of a side issue as i think all i need is to shell out for the 140 dollar tps unit... any ideas on the gas mileage tho as the spark plugs look fine... dirty injectors? could dirty intake cause that??

oh and just so everyone knows that 300km is mostly highway driving as i drive 45mins to and from school everyday on the highway...
thanks guys

trythis

A bad TPS will prevent you from setting the timing..
How old is/are your O2 sensor(s) That can casue a rich condition, which you might not have, but worth looking into.

stock87

Well, for us yanks, that works out to about 14MPG.

For starters, unless you've re-geared, your speedometer is going to be off because of the 31" tires. Even with a few rough corrections (really rough) that's still only 15MPG.

Something definitely isn't right. My carbureted 87 only gets those figures in 100% stop and go mile and a half in town commuting. On the freeway it easily gets 22 and I've gotten as good as 24 a couple times.

The TPS is a good place to start looking, because if it isn't set correctly, then the timing can't be set correctly, not to mention the engine will never know it's idling. Seach 4crawler.com for TPS info.

4x4countrygirl

Have fun with that TPS! I just had the same problem with my 94 p/u. Changed and replaced about everything you mentioned as well as parts of the EGR system, the O2 sensor, and the fuel filter. When I realized the TPS was bad, I got one and replaced it and we spent a good week trying to set it ourselves with a ohmeter and thickness gages. However, after a week of trying I gave up and brought her in to a local car repair place. Got it back and it still ran like crap! They set it to what they found it was supposed to be set at and still nothing! Brought it back in and they spent another two days on it (without any extra charge). If you can get to the screws, you can leave the engine runnin and slowly adjust the TPS to see where it idles smoothly but on my engine it's not too simple. However, if you said the TPS is not set (like they've said above me), it will make a difference once it is and the timing is adjusted. I was getting about 9mpg! Talk about frustration! I would definitely start there... GOOD LUCK!

MMA_Alex

definately get the 02 changed if it hasnt been, and get that tps set right. A can of injector cleaner cant hurt, and would probably help some too as im sure at that mileage the injectors are fairly dirty.

just fyi i get just above 20 highway with 32's, and the stock 4.10 gears so you should definately be able to do somewhere around 20 highway

Flash319

I have the same truck with 398k km on it and I can get milage anywhere from 550 km on a tank to 350-400km on a tank. I drive all highway 120km a day. If I go 110-120km/h I will get the lower number (30inch tires). If I go 90-100km/h I will get the higher number. The RPM difference is about 400rpm. Just try driving slower and see what happends. I just wish it was a 6 speed, would be better on the highway. This is also with a very old O2 sensor.

Also that irratic idle, up down up down is a bubble in your cooling system or you idle is to high. Burp the system and make sure it is full. Once you are in "open loop" (running temp) and your TPS idle circuit is closed (no throttle applied) your RPM must be under around 1000. If not it starts that up down up down thing.
Your idle will very a bit all the time because of coolent temperature. It is a mechanical diaphram system that sets the idle using the coolent temp to push a plunger closed with bi-metal disks. If you are flying down the highway for a while then suddenly stop the coolent is a bit hotter so your idle will be a bit lower and vise versa.

longhungsilver

hey guys sorry i couldnt get on my computer yesterday... was working away changing my front crank seal (again.. jsut changed it a few weeks ago when i did my timing chain)...but i sumhow pinched the inner part of the seal and it was leaking oil like crazy....

Okay but back on topic now.. My TPS is set right if checked it 3 times now and its set correctly... I do not know how old the O2 Sensor is but if it was faulty wouldnt i have sum other problems and perhaps a engine code?? Also i just did air care (live in bc canada...strick air polution rules)..and it passed just fine so if the O2 sensor was faulty wouldnt i most likely have failed????

I have run a can of injector cleaner through with no change in mileage or idle...

I have adjusted the idle correctly to 750 rpm (stock) and also tried 850 and 900 (currently using)...

My cooling system is air free as ive had to drain the coolant countless times for jobs these past few weeks and im always very careful to bleed the air out....

Also just to clarify my idle is rough when idling (wether ive been driving a lot and then stop...or been idling for a long time)... and this is after the engine is at operating temperture... And sumtimes (like today) when i start it up the engine will Rev up to 1700 then jump down to 900 then back up then down constantly until i rev the engine for a minute then it usually goes away... If i was to unhook the TPS connector the engine stops its odd revving but it idles at 3000rpm

any imput is much appreciated

longhungsilver

Countrygirl im very interested in your story... did u resolve it?? new tps unit or just readjustment?? Whats your MPG like now?

MMA_Alex

the o2 may not be bad enough to fail emissions, but still give you crappy mileage.

longhungsilver

even if the sparkplugs come out looking good?

MMA_Alex

if you're still running the factory 02 at 290k its probably pretty gunked up

maxpower_hd

I have a bad TPS and I'm getting 19 MPG with it unplugged. I've been too poor to buy a new one.

longhungsilver

just curious what does your truck act like with the tps plugged in?

maxpower_hd

It has a lag or hesitation in it during acceleration that kept getting worse and worse. I eventually went through virtually every test in the manual. I had to adjust the TPS. It would run good for a short while then would do it again. The 3rd and last time I adjusted it, I noticed that the readings would change by just pressing on the TPS. My theory is that it is not holding the adjustments. I unplugged it just to see what would happen and it ran a lot better.

I cannot find one in the salvage yards here and I can't swing the cost of a new one at the moment.

trythis

That shoudl be a sticky or go into FAQ.

Just think you can probably get 22 mpg with a new one.

longhungsilver

ya no doubt hehe.. mines not that bad but im pretty sure its my problem.. im gonna try runnin with it disconnected and see if that helps my idle