brian2sun

Hi everyone,

I'm a newbie to the site but I've had my 4runner for 8 years and 2 runners before that. My problem is lately my 97 4x4 3.4L AT 4runner has been bucking when I go up moderate grades and it also runs really rough only for the first 5-10 seconds after starting up. It sounds/feels like it's really loaded up or like it's missing.

Neither of these problems (the bucking or the rough idling after starting) is consistent. I can go up the same hill and 50% of the time the truck runs fine, 50% of the time it bucks - whether I'm really on the gas or just cruising. As far as the rough starting, it's about the same 50/50. It does seem that the issues are connected because when it starts bad, it almost always bucks later and when it starts good, I can't get it to buck.

About 3 weeks ago the CEL went on. I was glad because now I thought I would at least find out what's wrong and then be able to fix it. So I brought it in and they said it threw a P0303 code 2 times (cylinder #3 misfire detected). They checked the fuel pressure and compression - both good. They said the coil boots were the problem and replaced them. No CEL or codes since then, but the previous problems haven't gone away. Now I'm not sure if the #3 misfire and the coil boots were related to the other issues or not.

I've tried to bring it in again to the shop 2 separate times and both times the truck ran great for them. They told me to keep driving it until the problems start happening all the time and then they can fix it. I hate that and I want to at least try to figure it out before it grenades or leaves me stranded on the side of the road.

Here's what I've done so far:
-Cleaned MAF and throttle body
-Replaced battery
-Changed fuel filter
-Changed plugs and wires (all OEM)
-Changed coil boots
-Tested fuel pressure and compression - o.k.
-Changed A/T fluid, filter, gasket

Any help out there??

bgmac

what did your old spark plugs look like?......black/wet, brown, white?

brian2sun

2 of my old spark plugs in holes 2 & 4 were brown on the porcelin, the rest were white. They were bosch plugs and since then (4 months ago) I've been running the standard dual-electrode NGKs. I pulled them a couple days ago to see and they all look good still.

whokrz

I had a 1997 4runner with the 3.4 that was tossing P0303, it turned out to be the fuel injector. It took me forever to figure it out. You can test the fuel injector with a ohm meter. I found the specs in a fsm somewhere.
Here is a link to a bunch of toyota fsm http://ncttora.com/fsm/index.html
If it turns out to be your injector make sure you replace tall the orings/gromets on that fuel rail.

brian2sun

The shop I took it to also said they tested all the injectors so that doesn't seem to be the problem either. I just bought a new front o2 sensor which I'm going to put on tomorrow so I'll post the results of that. I have never replaced either of the o2 sensors and I've got 185,000 mi. I'm finding out that it's recommended to change them at 75,000 or so. I just figured that as long as they don't set off the CEL, then they must be ok. I guess many people have problems with them w/o them setting off any codes. We will see if that helps me...

Should I change the other o2 sensor too? I've heard that the rear one doesn't matter as far as engine performance goes.

4Runner202020

i was having the same bucking up hills along with a really rough start sometimes with the same code thrown and a month later blew my hg... check your coolant to see if it is discolored along with your engine oil. then get a compression test and a leak down test. my money is your about to have a blown head gasket.

bobby

brian2sun

The head gasket was changed about 3 years ago so it's possible, but I'm not thinking hg because oil and coolant look nice and clean. I have had a compression test and all the cylinders have good comp. I recently pressure tested my cooling system and that held pressure also...

brian2sun

Well the o2 sensor didn't make a difference so I bought a new coil pack (the middle one that has cyl #3 under it - the one that threw the misfire code) and so far so good. I'll have to give it a few more days though before I know.

brian2sun

So, the o2 sensor did make a difference after all. My truck has not idled rough after starting since I put it in. I was getting about 14.8 mpg (highway and city combined) now I'm getting 18.1! Those of you out there with old o2 sensors take note! Mine never threw a code, I just figured it was getting old...and it was.

I also diagnosed the bucking issue which is another thing that may help some of you out there. I was low on ATF. I know it sounds stupid but, I checked it several times in "P" (after shifting through all the gears, while running, after a 20 minute drive from a cold start on what I thought was a level driveway and it was always at the "full hot" level. 2 days ago I tried facing the truck the other direction after the same procedure and the dipstick read about a quart less than "low hot" on the dipstick. My driveway looks pretty level, but there is about a 2 quart fluctuation on my dipstick. I added a quart and it runs like a champ now.

Seriously, I asked my neighbor if my driveway looked level to him and he agreed it did. Just weird.

nc994run

I would also have a shop check to make sure your harmonic balancer is not loosening up. I was having a similar problem when my truck was above 4k RPMs and it was the retaining nut loosening up.

brian2sun

Thanks for the info. I will check the harmonic balancer.

SoCalPaul

What brand & where did you get your O2 sensor?

brian2sun

Bosch #13104. It was about $109.00 at Autozone. I'm not sure if it makes a difference, but I bought my truck out of Oklahoma. I believe the Ca. trucks have a different emissions system and may take a different o2 sensor. I'd call a Toyota dealer and ask first just to be sure...unless someone on here knows.?

brian2sun

Update:

The truck is still running great. I decided since it was my transmission (being low on fluid) that was causing the bucking, I would do a full service to it (and it's also been about 40K since the last fluid/filter change). There is an excellent write-up I found here on Yotatech: http://home.centurytel.net/stevenjac...sh/tranny.html which gives you step by step instructions with pics on how to drop the pan, change the filter/gasket and then flush the entire system (tranny and torque converter) without having to use a flushing machine, just the tranny's own pump.

I did the whole thing using 16 qts. of Amsoil Synthetic Universal ATF and the truck has never shifted better. I had more ATF on hand if I needed it - most people recommend using 20 qts. to flush, but mine was coming out nice and clean cherry red by the 12th qt. I stopped after 16 because I knew I was just wasting expensive ATF at that point. I really recommend doing this especially if your truck just doesn't shift as nice as it used to.

P.S. I thought this was weird..My trans is a 1997 A340F according to my door jam. The write-up is for a 2002 4Runner with an A340F. My filter looks different and the bolt holes (to attach the filter) are in totally different spots than the '02. Why does the '02 look so different? I always thought these transmissions were all the same.