HELP! Intermittent Stalling, tried everything.
 

Hello all, sorry in advanced for the long post. My 1998 4Runner has around 260K and she runs perfect except an occasional stall, once or twice a month. So here are the details, it always happens at a slow crawl or barely given a little gas, I mean barely then I release the gas. It happens without warning, no other symptoms i.e. drop in RPMs, hesitation, etc. When it happens all i see are the dash lights lit up. I drop it in neutral and she starts up no problem, then I drive away. The only other observation is it happens more often on warmer days, never when it's cold and shortly after I get off the freeway, I don't know if these things are relevant, just throwing it out there. BTW, no CEL Codes.

Ok, like a good forum member I searched far and wide and I could not find anything with exactly my issues. Based on my search and research, here are the things I have done. Thinking I have resolved the problem it happened again yesterday:

-Cleaned throttle body (Deep Creep)
-Cleaned MAF (MAF Cleaner)
-Replaced all vacuum hoses (silicone)
-Checked for vacuum leaks (solid 20 in.Hg at idle)
-Cleaned IAC Valve (Deep Creep)
-Replaced both 02 sensors (OEM Toyota)
-Replaced TPS (OEM Toyota)
-Reset ECU (Disconnected battery)
-Replaced spark plugs (OEM Toyota)
-Replaced spark plug wires (OEM Toyota)
-Replaced fuel filter (OEM Toyota)

I can't think of anything else, I'm stumped! The only thing I can think of it actually replacing the IAC valve or fuel pump, however I don't have any of the associated symptoms with those being bad. Other than that, my rig runs FLAWLESS...like a new car, idles perfect, no putting or hesitation what so ever when I floor it. I have Torque Pro with my OBDII Blutooth scan tool and my LTFT sits at 5% with STFT between -2% to 2%.

Thanks guys!

-Danny

I'd be inclined just to look at the ECU relay first.

It also could be the fuel pump as you hinted. I take it your 4runner never dies around town aka city driving or at slow speeds?

Thanks for the reply. I believe the EFI and ECU is the same relay right? And yes it never dies while driving around town. Why do you ask?

With knowing such now I'd be willing to say fuel pump. It just gives up the ghost for a moment after high speeds and dies, then once you place it in park and turn it over, no problem.

Another member maybe four to five years ago posted a problem similar with his 96, where he would be traveling on the highway and especially when taking a steep incline his 4runner would die. The motor for the fuel pump such was old and needed to be replaced. I am inclined to think he was good to go after replacing it. You would need a fuel pressure tester, a banjo connector, and a good bit of time to test it. There a few DIYs on how to drop the tank, replacement of the motor should be straight forward. Denso motor would be ideal.

The ECU and EFI relay are the same. Given that your 4runner is running fine around town, I'd wouldn't waste my time looking for a bad relay here.

Oh man i was hoping you weren't going to say that. I've read that these things rarely go bad, I guess I'm just lucky.

Hey LittleCaesar, after doing some more searching most guys who needed to replace their fuel pumps had issues with hard starts. Mine on the other hand always starts like a champ. Any thoughts? Thanks so much for your input bro.

-Danny

Bump.

I would replace the IAC and make sure the IAC seat on the TB is clean. IAC's can get sluggish and not react as fast as needed, especially at that kind of mileage. Its also directly responsible for controlling air into the TB. $80 is cheap money to throw at it before doing a fuel pump.

I figured my pump is about due anyways, you can get an Denso pump and screen that is OEM for $90 on amazon. If this doesn't fix the issue my next move would be to replace the IAC, which BTW is around $200+ for OEM Toyota.

Danny,

Without me being there to work with gauges and have a code reader that shows and captures live data, I am just basing what I know against the info you have given. For $90 that is a great deal on the pump, which I still think it is.

Yeah $90 for Denso Pump Kit its not bad at all. You gotta love Amazon Prime.

***update***
 

***UPDATE***

So I replaced my fuel pump this past weekend and it seems to have solved my stalling problem. While I had my gas tank down I also replaced all of the rubber fuel lines since I had access to them. I've never done this before so it took me about 5 hours by myself, not hard but took my sweet ass time to make sure I didn't forget anything. FYI, the Denso Fuel Pump Kit which cost me about $90 is exactly the same as the OEM Toyota pump which costs around $275. Thanks again LittleCaesar.

Glad to hear that the old pump was the culprit.

Kudos for dropping the tank. I hate changing fuel pumps (don't enjoy the smell of gasoline) so I end up wearing a heavy duty breathing respirator making me sound like Darth Vader.

Cheers.

DAMN!!!! I though I resolved this issue but the stalling happened again last week. This time while driving really slow around a parking lot. As soon as it stalls, I am able to start it back up no problem. So I replaced the IAC valve (OEM Toyota) and the stalling still persists.

LittleCaesar, you mentioned the ECU / EFI relay located under the hood fuse box. Do you think this could be the culprit? I've searched and could not find hardly any posts where these relays go bad on a 3rd gen, however I've found some where guys with the 1st gen 4runners have issues with them. Also, someone mentioned that there is another relay for the fuel pump inside the cab somewhere, they refer to it as a Circuit Opening Relay (COR). There seems to be some confusion as to where it is located. Do you think it would be worth my time to just replace both?

The only other things I can think of are the fuel injectors, coil packs, fuel pressure regulator, and coolant temp sensor. Other than the intermittent stalling, my rig runs perfect. Zero hesitation, starts perfect, and no codes. Sorry for the long post. Thanks.

I think that would be a waste personally. If a relay is gonna fail, it's gonna fail upon it being activated or deactivated. Doesn't make sense for a circuit opening relay or efi type relay to fail when the car has been running. Those are powered on when the key is turned on and they stay on. If I were you, knowing nothing else about the situation other than what you've posted, I'd try another maf. I know you say you've cleaned it and you have good fuel trims supposedly, but the situation you describe when it stalls makes me think maf.