3.4 hard to start when warm

Alright, so I just bought a 1999 4Runner Limited 3.4 2WD off Craigslist with 132,000 miles on it. 1 owner, and CarFax showed regular dealer maintenance every 3000-4000k miles. The timing belt changed at 88k, tranny and coolant changed 3 times, etc.

I test drove it before buying and everything checked out well, with the exception of the sunroof (was stuck closed). One of the hoses on the air intake (the 3-way attaching to the throttle body) that was duct taped, but it did not seem to affect anything at all, and that’s an easy, albeit slightly expensive repair. ($40+ for a simple hose?) Regardless, I was able to knock $300 off the asking price because of these things and a couple door dings here and there. $4500, including TT&L.

Of course, when buying used, especially from an individual, there are almost always things that you don’t notice until it’s too late. I found out the 3rd day after purchasing it, before I had time to do my own maintenance for peace of mind, that it had a hesitation issue when trying to merge into quick traffic; freeways and such. It did not happen all the time, but enough to be worrysome. I also noticed that it did not like to start when warm. It would turn over and start, but immediately die unless I pumped the gas pedal while cranking.

So this weekend, I did a lot of maintenance; I ran some Seafoam through the PCV vacuum port (only a 6th, not a 3rd; I’ve heard that Seafoam could spoil O2 sensors and I’d rather not overdo it), I changed the spark plugs and wires, changed the fuel filter, and removed and cleaned the MAF, the TB, and the IAC. I looked at the duct taped hose while I was in there and the crack didn’t even seem to go all the way through the hose. Regardless, I changed the duct tape. Haha. I’ll get a new hose before I renew the inspection. All the other hoses looked to be just fine.

I’ll change the fluids next weekend; I figured this stuff was a bit more important, seeing as to how it was considered ‘safety maintenance’. I’ll add some SeaFoam to the oil a bit before and run that.

After driving it to work today, I’ve decided that the hesitancy issue is now fixed; I floored it several times and never had one issue. However, the starting while warm issue is still happening. I had to get gas on the way to work (the flooring didn’t help that ) and when I started it afterwards, same thing. I had to pump the pedal to get it to start.

It obviously has something to do with Fuel/ air delivery. The Idle once started is great; right at 650 and smooth as butter. Even before the SeaFoam, it was smooth. I know that the TB does not have a choke like on a carburetor, but is there something similar? That’s all I can think of. Any suggestions?

 

Shot in the dark but id look at Fuel pump or fuel filter. I dont know why but I have a HOT issue aswell, mine will start to die after a soild day of driving or off roading then sitting at idle at light. Mojority of the the time the truck will auto compensate and adjust, but once or twice in the last 6 years its died. Happens completly random but only when its HOT outside in vegas and after the truck is HOT. At times in the past ive replaced the fuel filter and seem to fix the problem for 1 summer then comes right back. NEVER happens when its less then 100 degress out.

Id also Change out the both 02 sensors. Even if they are not throwing codes they may not be working properly. Also id take the CAT down and look in it. I took mine down and washed it with soap and water. Good to see there is no debris in there either.

 

I did change the fuel filter over the weekend, but not the 02 sensors. Fuel filter was definitely dirty. Definitely NOT a lifetime part, but I guess Toyota can't guarantee 250k-300k+ miles like most people see.
Is there a way to test the 02 sensors before changing them? I'd rather not throw money at parts if I'm not even sure they're the issue. On that same note, is there a regular changing interval for 02 sensors, and have I passed it/ am coming up on it? If so, I'll change them.
As far as fuel pump, why would it not work when starting hot? Something to do with the pressure in the tank?

PS: I'm not arguing you; I'm just curious and eager to learn.

 

02 sensors have about 100,000 life On them. There are ways to test them. But you have to look that up. Its past my knowladge in electronics.

Got mine from Amazon.com using Part numbers i got from Rockauto.com. I think I got em for about $60 a peice.

Fuel pump might just be a shot in the dark. ive only replaced mine once, but seemed like the fuel filter seemed to fix the problem for a little while. 132K on your truck id say you can probably leave it alone.

 

OP...what did your plugs look like when you pulled them out?? Your plugs will tell you a lot about the health of your engine. What did they look like?? Did you gap your new plugs before you installed them? And you didn't mention changing your PVC either.


Buddy...I would re-check your MAF and your connection. I've seen guys make their MAF worst by cleaning them...just an idea. Also, did you check to make sure a vacuum line didn't accidently come off/loose...and also check for any cracked hoses?? If all that's good...then maybe your fuel pump?? That's usually the first signs of a pump going bad...hard starts. But our fuel pumps are known for going the distance...very seldomly does one die...but there's always that one!?!?

I wish you good luck...I hope this helps. Hey, if you don't mind...when you figure this out, can you post what the issue was? Thank you Sir!!

- Russel

 

The plugs were pretty dirty, so I'm glad I changed them. That was one of the reasons for the SeaFoam; clean the insides as a just in case. The CarFax showed regular maintenance, but the PO may have ridden it hard in between. I'll add some to my crankcase later this week and do an oil change over the weekend. I gapped them too, to 1.1mm.
I did NOT change the PCV, no, nor did I clean it out. I realized that as I was packing up yesterday, but after spending most of the day working on the thing, I just didn't care then. Cheap and easy enough to do, though, so I'll do it soon.
To clean the MAF, ALL I did was remove the air filter box to get a good angle and spray some MAF cleaner right at the little sensor/wires. I did not touch them at all. I also spray electrical contact cleaner on all wiring harnesses that I worked with to clean them up.
All the vacuum line appear to be attached fine and appear to be in good condition. I didn't do a super detailed inspection, but seeing as how I was already combing through the engine bay, I figured I'd eyeball all of them.
Is there any way to tell the fuel pump is going bad, other than disconnecting the line to the fuel filter and hosing the poor person spotting under the car down in gasoline as I crank the engine? Any kind of electrical I should look for? I have a cheap multimeter, but I'm not very handy with it.

 

It sound like you did a great job at going over and tuning your 4Runner up. Especially with your MAF...I've seen guys wiping them down with paper towels or a red shop rag...and of course getting some kind of lent on or in between the wires.

As far as the fuel pump...unfortunately, I am unsure how Toyota checks theirs...It would seem you could just need to check the voltage at the pump and determine if it's good or bad. But yeah...you'll have to get with a Toyota shop/mechanic/maint.book.

Sorry I couldn't have been more helpful. Hopefully another member with the correct answer will chime in and help you!

- Russel

 

Thank you very much, RussToy. I try to do my homework before venturing into repairs/maintenance, just so I don't make things worse.

Which could be very ironic, since I have an update. So on the way to work, about 30 minutes ago, I turned onto the freeway feeder road and the 4runner stalled. I was able to get it over into a parking lot fine though. I checked under the hood, and didn't notice any leaks. I checked the new fuel filter, and it was nice and dry. After a bit of cranking, it came back on. Idled fine, I revved it to 5500 RPM just fine, so I pulled back out and went about my way. I noticed the smell of gasoline was very strong though. (To be fair, I thought I noticed it before, but I've been keeping a spray bottle of alcohol and a towel in the car to clean some grime off the interior at stoplights. The fumes kinda mix together; I love the rear window for ventilation.) It was definitely unmistakable this time though.
I got going again, and it stalled again once the RPMs got higher. Same thing, pulled over, cranked it for about 5 seconds and it fired back up. I was seriously considering the 02 sensors now. Ha.

I kept the RPMs low and took surface streets to work. When I got there, I popped the hood again to look for a culprit, and I found this L pipe on the passenger side of the firewall dripping pretty profusely. Not pouring, but it had definite flow to it. I believe it's gasoline, which would explain the smell, what I feel is worse mileage than I should be getting, and hopefully the stalling/ hesitation. The coolant and oil levels check out fine. Where does this pipe lead to, and should it be capped/ ran to somewhere?


I'd look myself, but I'm not exactly dressed for car work. If someone knows offhand or could check their own and a simple hose and hose clamp will fix it though, I'll deal and do it during my lunch break. I'll keep Googleing pictures, but this is such an odd angle, I doubt I'll find anything useful.


Edit: Is this actually the AC condensation drain line?

 

Ok, so ignore the post above about the drain line. Some fancy Google wording and I was able to figure out that it IS the AC drain line.
I neglected to mention it earlier, but after the second time that it stalled this morning, the CEL came on. I took it to Autozone during lunch and got the code P0172, which indicates that the Fuel mixture is rich in bank 1.
I'm seeing that it could mean:
1)injector or fuel pressure regulator leakage
2)Faulty MAF/Vaf sensor
3)ECT afaulty
4)Faulty H02S/AF sensor

I think that it has to do with the fuel pressure regulator, given the other symptoms: hesitancy and stalling under medium/hard acceleration, not wanting to rev, and hard starting. I just hate to throw parts at it that won't fix it and I hate to have to tell my wife that that *last* $100+ didn't fix the problem. Your thoughts?

 

Well that makes sense...its probably been doing it for awhile. Remember when I asked you about your old plugs...you said they were dirty. I take that means they were blackened?? Accentually, that shows you are getting too much fuel or an unclean burn. All the blackness on the plug is un-burnt fuel. Were all six plugs fouled? Be kinda curious to see what your new plugs look like? Also you might want to smell your oil...see if it smells of gas.

Hey Buddy...look on the bright side...at least you have an idea now as to what's wrong with it. You went from an entire vehichle down to 4 things!! I'm fairly sure you test the A/F sensor by checking voltage...Same with the MAF. As far as the ECT and the regulator...I have no idea. Sorry brother...

 

Yeah, the plugs were blackened; all six of them. I'll pull one of the plugs soon to take a look at it.
The truck is obviously running rich (there's not a gas leak, but I can smell it like crazy) but I'm just confused about the stalling problem. Could a bad 02 or A/F sensor cause stalling? I thought that when one went bad, the computer defaulted to 'limp home mode', which DOES make the truck run rich. Obviously emissions go up and mileage goes down, but I've never heard of stalling on hard acceleration. Could that flood the injectors essentially? I think the oil smells like gas, but to be honest, the gas smell is kinda overwhelming in general at times, so I'm sure if it was the oil or just an ambient smell.

Found something odd the day before yesterday; if I remove the negative battery cable (reset the ECU) then the car does not want to stall for almost a whole day (50-70 miles). The next morning, though, it will hesitate/stall if I give it too much gas, until I reset the ECU again. I'm to the point the past couple of days where I just remove the battery cable for a second every time I drive somewhere just in case.

Did some homework earlier. It won't rev above 3000 rpms while in gear. (It will rev to 5500 just fine in park).
I ruled out the MAF. Unplugged it with the engine running, and it died instantly. Was able to get it to start again after giving it a lot of gas, but it definitely ran poor. Stuttered a lot and idled pretty rough. Still the same rev limits. Catalytic converter? Crankshaft Postion sensor?

 

Is there some kind of rev limiter for these 4runners that could have gone bad? I know that some newer vehicles limit your revs while in park to limit unnecessary wear and tear. Does the ECU control this?

 

Sorry buddy...that's a question I can not answer ! I wish I had more knowledge so I could be of more assistance. I might be dropping by the Toyota dealership this weekend or first of next week...I could ask around while I'm there. That's about the best I got ....

- Russel

 

Nah, don't bother. Thanks, though, Russel.

I think I've figured out the issue.
I think the fuel pressure regulator is faulty.
I had to remove the Intake Silencer earlier and i noticed that it had gas in it! It may have this whole time and I just never tipped it all the way to have it spill out when removed! This means a bad FPR, correct?
So...I hope that I don't blow up or something while I order a new FPR.

Other question: should I go OEM (even used goes for like $60) or will an aftermarket be OK?

Like this:
Universal Red Adjustable Fuel Pressure Regulator Gauge JDM FPR 1 1 0 140 PSI | eBay

 

I know it's exspensive, but I always but OEM Toyota parts...even if I have to buy used. The way I justify the cost...that part you're replacing worked for 132,000 miles. Ask yourself, how long will that cheaper Chinese part going to last?? Every once in a while you'll get lucky and get a good Chinese part...but on the average you get junk. Then you are right back at square one. I'd just assume replace with OEM parts and never have to worry about it again. Just my opinion.

Good luck. Hope this fixes everything for you!! I'd be carrying a fire extinguisher, just to be Careful!!

 

I ordered an OEM off eBay. Should be here by Friday. This makes sense; hopefully it'll fix everything.
The Intake Baffle fills with fuel leaking from the FPR while it's running and I guess essentially 'vapor locks' itself. This fuel starts to evaporate and makes it hard to start because the engine should be getting air from this intake, not fuel. Once it's running, it runs OK because the majority of the evaporated fuel is gone.

 

So did the FPR solve your problem?

 

Did this fix your problem ??