2+ year mystery of the P0304 code...

[gotdurt]

I picked up a clean 2000 3.4 in December, so I'm still new to these trucks... being someone who likes to drive older vehicles, I've found that for most issues that arise in vehicles over 10 years old, they seem to be common issues with that model, more often than not... I hope that's the case here. I've done some searching on hard starting for these, but found it tough to wade through the sea of dead battery stories, etc to find to anything of use...

So, shortly after buying the 4R, I noticed that, occasionally and randomly, sometimes a couple of times a week, sometimes only once every couple of weeks, it took a little extra turning to start. Once it fires, if you let off the starter too soon it would die. Then once started, it would run fine, no codes thrown or anything. It has done this since early December, but wasn't a huge deal, so I figured I'd do plugs and wires, clean the MAF sensor, etc when I get a chance and see if it helps anything... "when I get a chance".

A couple of weeks ago, however, things changed a little; when it had an episode and finally started, it would run rough... I'd turn it off, then restart and everything would be fine... still randomly though, and never at a convenient time for some testing...

So the other day I go to take my son to karate, and it has an episode, runs rough, and I kill it, restart... still running rough... try again... still... I didn't have time for this, so I drove it. The CEL finally came on while shaking at a stoplight, and stayed on, so I dropped my son off and ran over to a parts house to pull the codes: P0300 & p0304. Gotta love vague codes, but it's a start.

It started and ran great after that with out any more episodes. The next evening I pulled the #4 wire and coil, and found the contact to be extremely corroded; I suspected that this might be the issue, but wasn't equipped to properly clean it at the moment, plus I planned to replace the wires etc this weekend anyway, so I did a little scraping and moved on to swapping coils to see if the code would follow. In the process I also noticed that the #6 wire and coil contacts were in similar condition as well. I reset the ECU and the EFI, and it ran great for the next couple of days.

Tonight I stopped at a store, and when I came back out, it wouldn't start... it would fire, but not run. I finally got it running, but no codes were stored :mmph: It drove great the rest of the way home.

I hate these intermittent issues, because you can't reliably test anything; you pretty much have to take an educated guess, then wait and see. I plan to change plugs and wires tomorrow, but I'm not holding my breath...
Meanwhile, I'm hoping that there's a common issue with these things that will at least give me some direction that might help me avoid spending the next couple of months "trying things", or until whatever it is finally quits for good at a very inconvenient time and location...

 

[LittleCaesar]

Try also cleaning the throttle body, and if that looks less than stellar, plan to pull off the IAC underneath it and give it a good cleaning as well.

But start with the wires (NGK, Denso or Sumitomo) and plugs (NGK or Denso dual electrode).

 

[jgue467]

... I'm hoping that there's a common issue with these things ...

No common issues. Man my short attention span wouldn't allow me to read all you wrote but have you run some fuel additive/upper engine cleaner like seafoam or startron in the fuel? Otherwise its +1 on what LittleCaeser says. IAC is suspicious too. Keep it weird austin - looking forward to sx... :cowboy:

 

[subiedrewbie]

I'm having the same on my wife's 99 3.4l. Im getting a lean code, but think that is Maf. The warm start issue seems to be linked from the IAC. Like these guys said, I will be starting with the cleaning of the iac and throttle body. Good luck

 

[hondafmx1000]

My T4R had the same issue a while back, it still has a hard start but it threw p304 code multiple times. I changed plugs wires and coil packs there was no improvement, however after doing enough research i changed the injectors and the misfire went away. Like I said my 4runner still hard starts but there is no misfire. This may not be the case for you but I would eventually look into the injectors if you do all the other troubleshooting and it doesnt work. Good luck, replacing the injectors isnt hard but its a pain in the ass. hope this helps.

 

[Grenvilleter]

Take a look at the fuel pressure. A weak fuel pump could be also causing hard starts as well.

 

[gotdurt]

Sorry about the long post above, but typing out the full progression of symptoms sometimes helps me troubleshoot.

Well, I did plugs and wires today. I also cleaned the throttle body and and MAF while I was at it, even though they weren't in bad shape and I don't think were likely culprits or contributors anyway, given the intermittent nature (at least for the throttle body). Plugs looked good, but the contacts on the coils for 4 and 6 were heavily corroded, and the #4 wire was missing part of the female coil connector... I don't know if that was a coincidence (p0304), or the culprit, guess we'll find out.

As for hot starting, this issue doesn't seem to care about temperature; sometimes it'll happen on a cold morning, sometimes when stopping for 5 minutes after running errands all day. Something is failing/malfunctioning intermittently; possibly mechanical, but I'm betting electrical. An injector, or even fuel pump would make sense (at least for hard starting), although I'm not sure yet how fuel pressure before the rail would cause a misfire in only one cylinder... if it throws another code and doesn't follow the coil (would be p0306 now), I'll go ahead and replace the #4 injector. It does seem that failing injectors in these seem to be a fairly hot forum topic...

Edit: did some searching on fuel pumps and it seems that these tend to get tired between 150-200K miles, so I might do it anyway, since I'm at 195k. It sure wouldn't hurt anything.

 

[gotdurt]

Okay, so yesterday after the "tune up" and cleaning, I went out periodically and started it, at least half a dozen times, and it started and idled as good as it ever has, if not better, every time.

I went to run some errands today, and it started and ran just as well, until I got to the 1st store; came back out and although it fired off and ran almost immediately, it had a very weak idle, although throttle response seemed normal, and it didn't die when I put it in gear. I killed and restarted it several times with no change. So I drove it... again throttle response was good, and acceleration was normal, if not somehow slightly better, and idle returned to normal after driving some. This is a change in symptoms. It did this for each of the next 2 stops, then after the last stop it idled normally from the start. No codes were thrown, and no individual cylinders seemed to be missing at all. After getting home, I tried starting it after letting it sit for various periods without any additional issues.

So, behavior has changed a bit, but I don't know if it has something to do with what I did to it yesterday. Now I'm suspecting the IAC, or maybe some of the gunk from my TB cleaning ran into it... Also think I'll change the fuel filter, as it appears to be original, might be a little restrictive, although I would think that low fuel pressure would affect the way it runs in general, not just starting and idling.

Also, I'm considering the idea that maybe the misfire codes were a separate, unrelated issue to the intermittent hard starts, and just coincidental...

 

[LittleCaesar]

I would tackle the IAC next. Also consider a fuel injection cleaner such as Royal Purple or BG 44k, take it for some spirited drives, then change the oil sometime soon thereafter. Then change the fuel filter, using an OEM filter.

Unless the code comes back for a misfire, I wouldn't think about it too much.

 

[gotdurt]

Well, I'm at a loss now, and it got worse today, 2 days before we are to leave for a Spring Break trip to NM. It starts if I put my foot down, then idles at about 300rpm; you can barely hear it run. If I can get it in gear without it stalling and drive it for just a few seconds, idle will return to normal. Throttle response is still normal, even at 300rpm; no bogging or anything. Still no codes.

The way it has progressed, I'm leaning toward the fuel pump, except in past fuel pump issues (with other vehicles), it affected throttle as well as starting/idle. I don't have a way to test fuel pressure any time soon, or other testing, frankly... if I'm going to have to replace the pump, I'm going to have to take the day off tomorrow to get it done, no time for troubleshooting. I don't want the pump to leave me and the kids stranded in west Texas... I could buy a pump and carry it with us, but I'd rather do it in my driveway with a jack than on the side of the road... did I mention that I also filled the tank today? Yep.

I checked and my local Advance has Airtex and Bosch pumps in stock, and Oreilly has their own "Import Direct" brand in stock; $134, 148 and 111, respectively. I can get a Denso from Rock Auto for $73, but it's too late to get one. I'd rather not buy a crappy one for more $, lol... I could just buy one and take it along for emergency, and if I don't need it, return it and order what I want when I get back...

If the IAC is malfunctioning, it won't leave us stranded, but just make starting difficult, which I can work around. Being intermittent, though, I can't really test it to know.

 

[gotdurt]

Autozone has a Delphi for 135, think I'll go that route and dive in tomorrow... at least then I know I won't be dropping a gas tank on the side of the road.

 

[Neil_R]

Have you checked for vauum leaks? Can't hurt. Does sound like a fuel pump though. Sometimes they are intermittent.

 

[gotdurt]

Have you checked for vauum leaks? Can't hurt. Does sound like a fuel pump though. Sometimes they are intermittent.

Yea, did that at the beginning, couldn't find any leaks. The way the symptoms have evolved and get progressively worse tell me that a component is failing.

Also, I found a couple of threads like this one that sound similar to my situation, before it progressed:
http://www.toyota-4runner.org/3rd-gen-t4rs/108583-replacement-fuel-pump-3.html

Just picked up the Delphi pump, plan to jump on it first thing in the AM.

 

[gotdurt]

I got a late start, and of course what I thought would be a straight forward job has been a royal pain, and I haven't even unbolted the tank yet. The middle compression fitting on the main line is all kinds of jacked, so I disconnected it at the filter... I somehow lost about 1/4 gal from that line (on other jobs I got short a trickle)... BUT, the problem line is one of the other 2 on that side, with the clamps; so far I have collected about 2.5 gallons from it, and it is still going! Luckily I had a couple of empty 1 gal cans and a 5 gal, handy, but I'm concerned about running out of cans...

Meanwhile, I can't do anything until this stops, and it is a slow trickle... starting to think I should have driven it a couple hundred miles last night. Funny, the last time I did this on another vehicle, I had just filled the tank then too :ybrick:

Now to look for something to cap it with.

 

[gotdurt]

Wow, going on 7 gallons now, lol. My wife came home so I could empty the cans into her car and keep it going... I might just end up with an empty tank anyway

edit: 3:30; 12 gallons and flowing... At least it looks like I might get to drop an empty tank...

 

[gotdurt]

Well, at least I won't need a fuel pump for a while; that didn't fix it.

Started it up and let it idle for 10 minutes or so, then killed it for a few minutes and tried to start it again, same problem. At least now it is becoming more consistent, so maybe a shop can diagnose. Until then, I'm about to drive it a couple thousand miles in the next few days... hope it's nothing that can leave us stranded.

 

[hondafmx1000]

Check the injectors. They're a little bit of a pain but not nearly as bad as what you were doing. Is there any codes anymore?

 

[gotdurt]

Check the injectors. They're a little bit of a pain but not nearly as bad as what you were doing. Is there any codes anymore?

No codes since that one episode, I think that was solved with new plug wires, since the #4 wire was in bad shape and the code was P0204. I think it was coincidental that it happened wile dealing with the other issue.

Before I left, I pulled the throttle body and IAC valve again and did a more thorough cleaning on the valve to make sure I didn't miss something the first time, and this time I also tested the actuation... the movement seemed more limited than I expected, and didn't seem to fully open and close. I buttoned it back up and decided that for the trip I'd just leave it running whenever it was practical (like gas stops; yes, I know, "don't do that"). I had also primed the fuel pump with Sea Foam and dumped the rest in the tank, so I figured I'd wait and see if that did anything.

Headed for NM the next day, and shut it down for a gas stop in Big Spring. It stumbled a little when I started it, but a goose on the gas and idled fine.

I stopped for dinner at the border, and to my surprise, it started right back up. I decided to start testing it from there... over the next 5 days it started every time... still not as quickly as I'd like (my old CR-V started as soon as I bumped the starter), but consistently and reliably.

On the way back, I stopped at the same station in Big Spring, and it stumbled again...! I'm wondering if it is oxygen related, since it improved as the elevation rose, and vice-versa... It didn't do it again for the next couple of stops though.

On another note, this was my first significant trip where I could play the gas mileage game... I got a worst tank of 20.1 (this involved mountain driving as well as some driving on Jeep roads to and from our camp) and a best tank of 24.6 (flat desert running 65), for a trip average of 22.3 mpg. That's also fully loaded with camping gear and kids. Actually the last tank would have probably been the worst because I was running 75-80 on the last leg home, but I haven't checked it yet. Anyway, with those numbers and considering the vehicle, I'd say it's running properly other than the idle issue. I'm eager for a pure freeway test now (no towns with stoplights), to see if I can break 25 :thumb3:

Guess I'll wait and see if the problem returns now that I'm back close to sea level. If so, I might go find a salvage IAC and see if it tests different that mine.

 

[LeeMajors]

Mine has a longer start in cold weather--fires right up in warm weather. It was a bit surprising initially since my old 4cyl Tacomas fired right up, but it turns over like 3-5 times before kicking over.

Lots of folks seem to think this is more-or-less normal.

 

[gotdurt]

Mine has a longer start in cold weather--fires right up in warm weather. It was a bit surprising initially since my old 4cyl Tacomas fired right up, but it turns over like 3-5 times before kicking over.

Lots of folks seem to think this is more-or-less normal.

I'm beginning to wonder if it's "normal" myself. My wife's Scion was the same way when we got it, 2 years later nothing has changed. Maybe it's a Toyota thing... it' not like it's hard to start, maybe 2-3 turns, just doesn't fire as soon as you twist the key like my other vehicles. Temperature doesn't make any difference on mine. I just didn't notice it when I was test driving other 4runners... doesn't mean it didn't happen though.