Intermittent Stalling

Hello all,

I've been having a problem with my truck intermittently stalling at idle/in traffic off and on for about a year, and it has gotten to the point of 3-5 times a day now. I've dug through every thread I could find on this topic, and am getting tired of throwing parts at the truck.

First things first, '99 Prerunner with the 3.4 5VZ, zero motor modifications @197k. In Drive, with foot on the brake, idle will stumble, drop to 300-400 rpm, then die. If left in park, idle will become low and rough, then sputter and die. If the idle starts to fluctuate in park and I put it into Drive, it will immediately die.

I've tried the following:

-New MAF Sensor
-New Throttle position sensor
-New Plugs & Wires
-Thoroughly cleaned Throttle body & IAC Valve
-Ohmed IAC Valve, is within spec
-Sprayed carb cleaner on all vacuum lines, no signs of leaks
-Replaced valve cover gaskets (leaking), replaced all intake manifold gaskets and air filter while I was in there
-New Fuel filter
-Seafoam through vacuum lines
-Injector cleaner through 5 tanks of gas
-Compression test, all cylinders within 10psi of each other

It's not throwing any codes, and it does not make a difference if the A/C is running or not. I'm starting to suspect the fuel pump due to a slight hesitation in the throttle when accelerating from a stop, but it seems like the fuel pump would be an all or nothing deal, not a long intermittent issue.

Does anyone have any suggestions or ideas? Any and all are welcome at this point!

The problem child:

 

How does your transmission shift? almost sounds like a torque converter stalling out. I know you said you cleaned the injectors. Could be a bad one. Unfortunately not an easy way to test them.

 

Transmission shifts fine, torque converter wasn't something I had thought about. On the extremely rare occasion that I'm over 3500 rpm though it feels like there is a loss of power, not sure if it could be slipping up high and stalling down low?

 

You installed the TPS so it's sensing the idle position correctly?

Could be the EGR valve is stuck open.

Maybe the fuel pressure regulator. Test the fuel pressure at the rail.

 

TPS is fine, runs just like it did before lol. I'll look into the FPR, thanks guys!

 

How many miles?

If its like my 99 model Prerunner, it has no EGR.

 

My first test would be to check the brake booster. with the motor off, press the brake pedal until all vacuum is released from the booster. With your foot on the brake, start her up. the pedal should drop slightly. take your foot off the brake and let her run for a second or 2 and shut it off. Now press the brake pedal, you should get 1 1/2 to 2 pedal pumps before the pedal gets hard. If it is hard immediatly or 1/2 down on the first pump you need a booster as you have a large vacuum leak.

your best friend in this case is someone with a decent OBDII reader, I prefer a bluetooth connection to an iPad myself... just because there are no codes stored does not mean that there isnt any diagnostic information that can be obtained with the tool. You have to start somewhere and having said that this is where I would start with the OBDII tool. I would check to see if all of the smog monitors have run and she is ready for smog. If the monitors havent run and she shows a P1000 code means that the PCM is loosing power/ground. 99% of the time the KAM, keep alive memory, retains the info, sometimes it does not, this is a clue. If the monitors have run and with the the device in the scanner port and linked to you device I would monitor coolant temp sensor and intake air temp sensor data and see if they go crazy as she shakes and stalls, again, a clue. The better OBDII tools will graph the data so that you dont have to watch the screen all the time.

on the intake manifold drivers side there are 6 or 8 ground wires on 2 ring terminals, one by one wiggle each wire slightly and give it a little yank. These are suseptable to damage due to their location. The wire can be broken internally and show no signs on the insualtion. These wires are the grounds for the PCM, injectors and other important stuff.

1. after she stalls and you start her does she start immediatly or do you have grind the starter to get her going? My thinking here is that if you have to grind on the starter like she is flooded I would pull the vacuum line off the charcoal canister purge line and plug it and drive it. If the control valve sticks or is intermittant it could be a problem. we are looking for an intermittant and that is the most difficult to diagnose. If she was just plain ole' broke, thats easy to diagnose.

 

Great post, I did not think about a vacuum leak at the brake booster. I'll check that today, I have new injectors on the way to rule that out (200k on the originals, so it probably won't hurt either way). If the brake booster is okay, I'll check those grounds. Scanned it with a nice OBDII reader and had no stored or pending codes.

After a stall, it will start easily. On a hot start, it honestly seems like it starts too early(?), as it fires up after 1.5 cranks and seems to stumble up to idle.

Once again, great information and I'll keep this thread updated with what I find!

 

Another thing that I've noticed; while the stalling is intermittent, it becomes more frequent the longer I drive the truck. I.E. sometimes it drives perfectly fine for the 15-20 minutes to work, but if I have a 30-45+ minute drive it will start to idle poorly and stall at a stop. If I'm stuck in traffic for a long time, it can get to the point where every time the truck comes to a stop, it will die. This has stumped me, but if that's a clue for anyone more familiar please feel free to chime in! The knowledge base on here has been awesome for keeping this thing going.

 

just because it isnt setting a code doesnt mean that there are any codes pending. Each code has a certian threshold that has to be exceeded before the MIL light is turned on. Some codes are cleared as soon as the key is turned off. A decent OBDII scanner should have the ability to read pending codes. The issue is when it happens you are either in traffic or cant pull over and try this or try that... this is going to be difficult to track down. I know of no other way to check for spark other than putting a plug in a removed plug lead and crank it over and watch. If you have spark then it is fuel or an "electrical gremlin". A 1/2 second squirt of starting fluid in a decent vaccum line into the intake will tell you if it is fuel related... no more that 1/2 and you risk blowing the boots off the intake if it backfires. If there is no spark the first suspect would be a crankshaft position sensor. Dont run out and replace it just because I mentioned it. If yours has a tach watch the tach needle during a restart attmpt. If the needle wiggles a little, the cranksensor is probably OK.

 

Have you checked fuel pressure? Sounds like the fuel pump is on its way out. Check the pressure before spending more money on parts

 

I will check fuel pressure today as well. Glamis, that's a good point about codes clearing once the key is off. I'll check spark as soon as I can, and like you said that should narrow it down a bit more.

 

Grounds and brake booster checked out okay. Picked up a fuel pressure testing kit from oreillys, but had a few questions. Can I test the fuel pressure right after the fuel filter, without having to deal with the banjo bolts and fuel rails? If the pump was bad, it seems like it wouldn’t matter if I was upstream of the fuel pressure regulator.

Speaking of the FPR, I pulled the vacuum line between it and the box on the intake tube. It was slick, and smelled like gas. Is this a sign of a bad FPR? If so, I will still test the pump at the filter, but seems like that would be a culprit.

 

So it only stumbles and dies when you come to a stop? and not while driving?

Have you tried putting it in neutral before you come to a stop?

Still kinda smells like a torque converter issue...

 

In neutral and park it will still start stumbling and die, after I checked that I somewhat ruled out the torque converter

 

Yes. Gas should not be getting past the diaphragm into the vacuum hose. Easy to test with a hand vacuum pump. It should hold vacuum.

 

After waiting for parts to come in, I replaced the fuel pressure regulator and injectors last night. Did all 6 with temporary eBay ones (I know I know, going to send originals to witchhunter and reinstall, just can't go without the truck in the meantime). Job wasn't too bad, considering I was just in there for valve cover gaskets and everything was fresh in my mind. The 17mm banjo bolts were tight as hell, and a bitch to get back in but all in all took about an hour and a half. This writeup: http://mattshowto.blogspot.com/2009/04/how-to-replace-fuel-injector-on-toyota.html was great for reference. Have only driven the truck about 15 miles since then, but hesitation off the line is gone and seems to run much better.

Fuel pressure regulator was definitely shot, once I removed it gas poured out of the vacuum line on top. Got an OEM one off eBay with ~140k miles on it for $40, I appreciate all of the advice from y'all on here and will keep this updated if need be!

 

Well, after a couple days of driving the truck the intermittent hesitation on acceleration has returned, and motor is running rough again. Going to be backtracking and checking my work, and testing fuel pressure from the pump. Will update with results

 

How many miles did you drive before the hesitation came back?

Maybe the used fuel pressure regulator is bad too. Did you test that it holds vacuum when you got it?

And did you replace all the rubber gaskets and grommets on the fuel injectors? The repair manual says they are non-reusable I believe and they could cause vacuum leaks.

 

I didn't track it exactly, but probably ~50 miles. I'm going to rent a vacuum pump today and check it, which I should have done before putting it on.

As far as the injectors, I have the eBay ones on it right now and they had all new gaskets/grommets on them. If the fpr holds vacuum, I'm holding the cheap injectors highly suspect at the moment. Seems like there's a pretty good chance they could be bad from the start, and if the fpr is good I may swap the OEM ones back on. If that solves it, I see no reason to send them off for cleaning if the problem was the fpr in the first place. Should've just changed one thing at a time lol, but figured I'd do it all since I was in there already.