TexFF

I've searched for hours on google(& here) for a good answer to my question(s) but have yet to find a positive, definitive answer. I recently puchased a '93 4Runner 4x4 w/a 3.slow, 5 speed tranny, 4" bracket lift & 33's. I have codes 14 & 25. I've read a lot of these trucks have the DTC 14 w/no problems so I'm not too worried about that one(unless I should be!). DTC 25 (continuously lean is what the scanner said) is what I'm trying to fix. I checked all vacuum lines, no leaks. Distributor cap appears new as well as wires. O2 sensor appears aftermarket universal(wires spliced). Fuel filter appears original.
Symptoms:
runs normal cold (1,400-1,500 rpm's)

idles high when warm (1,050-1,100)

cuts out/hesitates when warm upon acceleration until about 3K RPM then it has full power & runs a lot faster

when on highway @ steady speeds it speeds up for about 10 seconds then slows down for 10 seconds & repeat(like it loses power, then regains it, then loses it, repeat)

I ordered a Denso O2 sensor & a fuel filter, that will be here next week, in hopes of correcting the lean issue.
I know a ton of people have asked about these 2 codes but my questions are a little different:

with my description of the way it's running does it sound like the O2 sensor or the fuel filter is the culprit?
if one of these correct the lean issue, will it automatically lower my warm idle(currently 1,000-1,100), to the correct RPM(800 +/-50)?

Any other ideas/tips/advice? I'm not new to wrenching or 4x4's but I am new to Toyota(I also have a '10 Tundra 4x4 but it has zero problems!) Thanks.

***UPDATE*** After about 200 miles I'm convinced the problem is solved. Restored HP, better fuel mileage & no DTC!!!!! Not sure if it was the new Denso O2 sensor or the new fuel filter but it was 1 or the other!!!!!!!!!!!!!!!!!!!!!!

TexFF

Also, the problem is intermittent. But it is getting more frequent and worse. Noticed this morning it's doing it when the engine is cold, too.

Dirt Driver

The missing and hesitation doesn't get even worse with more throttle, then it's probably not the fuel filter.

TexFF

It definately gets worse with more throttle. As I try to accelerate is when it's most noticeable.

Team420

u said "appears" a lot in ur og post..... That means u really dont know... correct? Satrt simple, and work from there... Have u checked the rotor in the distributer? Compression test done? ohm tested the wires? pulled the plugs to listen to what hey tell u?

TNRabbit

Lean condition can also be an unmetered air (vacuum) leak....

aa1911

iTrader: (1)

I wouldn't waste time at the fuel filter based on your description. O2 sensor I bet will help but as mentioned already, I would check plugs/wires, vacuum, compression test, etc. and try to find a problem. then on to injectors possibly...

a lot of folks mess with the timing on these also...

TexFF

A few points I should point out:
removed - batt. cable to erase codes the other day. Now there's only the DTC 25(wasn't worried about the DTC 14, anyways). I will check plugs & rotor today. When I say assume the cap is new it's due to the fact the cap & screws look brand new, unlike the majority of the parts. If it was a compression issue, it wouldn't do it intermittently so not worried about that. ALL vacuum lines are good! If it was cap, rotor, plugs or wires wouldn't it be running RICH, due to incomplete combustion???? Original fuel filter has 173K miles. I'm replacing it anyways. Why should I not? Thanks.

Dirt Driver

I only just now looked up the code 14 since I don't have them all memorized. It means the ignition signal to the ECU is dropping out for at least four consecutive ignition events at a time. You do need to find out why that is happening.

1.) Perhaps. Rich, lean, and ignition misfires all look like a lean condition to oxygen sensors. That could mean that the ECU was commanding more fuel in response and making the misfire worse, or maybe it has to do with that code 14...

2.) No reason not to with that many miles.

TexFF

Just checked plugs, wires, cap and rotor. All good and all new. It appears the PO was chasing this same demon I think. I hear ya about the lean code due to ECM adding more fuel. Sure hope it's the O2 sensor or fuel filter. If not I'm at a total loss. Btw, the code 14 is now gone after clearing codes and driving about 100 miles. Thanks.

TexFF

Just changed O2 sensor & fuel filter. I'd sure like to beat down the genius who decided to put that fuel filter there AND the PO for never cleaning the bottom side of this rig!!!!! It SEEMS to be running w/more power now but may be wishful thinking. The idle did not drop so I'm about to figure out how to adjust it. It hasn't acted up for the past few days so I won't know until it throws, or doesn't throw, the code 14 again. Appears to be running strong, though. Weird thing when I was removing the old filter: the fuel going into it was dark(like whiskey) & the fuel in the other side was clear(like vodka). I'll post back in a few days on a final conclusion.

Dirt Driver

The brown fuel may have just been backflow from a dirty filter.

TexFF

If so then that filter was nasty!!!!

petslug

ck.your idle mixture sensor/i had the same problem that was the culprate