5vzfe Stutturing at stop lights & low rpm while driving.

Hey guys, looking for some input from ppl smarter than me. I’ve done some searching and I’ve got an idea for troubleshooting to start.

side story, I was about 100 km into the mtns doing a trail when my truck started doing something odd. When I would let off of the gas after crawling up some inclines, it was as if my rpms would drop quickly and truck would stutter a bit. After the stutter it felt like a bit of a ‘pop’ of power and it’d be fine. It repeatedly did this, so I immediately booked it down the mountain and drove home.
On the highway, when cruising at about 90-100km and in 5th gear, if I let off the gas a little bit I’d feel the same kind of issue. I made it the whole 6 hr drive home, and it seemed to get better as I went. Until I got into the city and at every red light as I’d slow down to stop it would do the same thing. While it’s idling and I’m stationary it seems to be fine? I’ll start the truck up even cold and it is totally fine.

- Maf is new 3 months ago, I cleaned it just in case
- TB swapped in about 3 months ago, and it was spotless plus the IAC was cleaned out too. New Oring.
- plugs, wires checked and good.
- new vacuum hoses 3 months ago. Checked again all are tight.
- engine coolant temp sensor has been ordered. I saw someone explain something very similar.
- it runs totally fine so I don’t expect a fuel issue. Am I wrong?

Anybody experience something like this? I’ll be honest, I was sweating buckets thinking I would be stranded out there. Luckily I’m well prepared, satellite comms, food, shelter, and a diesel heater to stay warm…

 

And this is where I was..

 

I think you're gonna want to pull any codes it may be throwing. Be a bit wary of the parts stores trying to pull the codes. I just had a friend who's 2000 V6 Tacoma was running like crap. He went and had O'Reilly pull the codes they found nothing (no codes). He took it to a local Toyota mechanic and he was able to pull a code for the TPS. New TPS and the truck is running great again. Might help you target your troubleshooting. Also probably worth checking all your grounds

 

I shoulda mentioned, no codes.. I do have the elm327 and app nothing was showing even while it would happen. When I got home I tested it with my good Bosch scanner and still not a thing.

 

Sub’d, I’m have the same set of symptoms. New plugs and wires, clean MAF, MaxBored TB, cleaned newish IAC, just replaced ECT with a new OEM one. Next to check is coil packs and TPS.

 

Just for fun-sies, try pulling out your pcv valve and plugging it off then go for a short drive to see if it still happens

 

Oh I also installed a new PCV valve and hose. Maybe that's faulty?

 

Are your RPM's flucuating at idle? For me I needed to clean out my fuel injectors. I was having this problem for a while but it was only noticeable when stopped at lights.

 

Mine does not fluctuate at idle but occasionally I’ll get a higher-than-normal idle when warmed up; around 12-14k. It only happens rarely and will go away when I restart the vehicle. I used an eBay IAC which could be failing. I know the IAC is supposed to open when you let off the throttle.

 

Wanted to update in case anyone else is still struggling with this. I think I got the bottom of the hiccup/hesitation/misfire/hard cold starting issue I was experiencing. Borrowed my friend's 3rd gen 4runner yesterday and tried all combinations of coil packs and spark plug wires. His wires/his coils, my wires/his coils, his wires/my coils. Turns out the Denso wires I installed about 8 months ago were faulty. Went to Napa, got some blue NGKS, now she purrs like a kitten.

 

Great thread, Great info, thank you for sharing!

Peter

 

I've been battling this for about 6 months now and it's been getting steadily worse. I did plugs and wires like 20k ago so curious if the ngk wires or plugs are going bad. Packs are og (240K) so could be losing one of them as well. My initial thought was a dirty iac, but pcv could be the culprit or even a small vacuum leak. Need to carve out some time and start troubleshooting like OP sooner rather than later, had it stall out a light the other day.

Not having a single code being thrown is really the most frustrating part of this.

 

It seems that some people get lucky with non factory secondary cables and some dont. The issue that I have experienced is that even with the truck missing right in front of me and the scanner in Mode 6$ the scanner does not report a misfire. This is with both of my Snap On scanners too, not a $35 harbour freight special. Not sure what the PCM is using for testing parameters so this makes diagnosis just that much more difficult.

 

I wasn't getting any CEL and the miss was intermittent but mostly prevalent when the truck was cold. All wires passed FSM tests as did coils and other sensors. Took hands on process of elimination to nail down the issue.

 

Will definitely try this. A buddy was parting out a 5vzfe, so I grabbed coil packs, wires, and tps, but mine were fairly new.

Oddly enough, this past week I haven’t had the truck show any symptoms at all.

 

Ahhh, old school. A warm afternoon, a radio and an ohm meter that you trust.

 

Welp update to the update: the momentary power loss is still happening regularly now that winter is here. It’ll happen a few times until the car is good and warmed up. Back to the drawing board…

 

A large part of diagnosing problems is understanding how the system works as a whole. By system I mean the fuel system, both low and high pressure the ignition system, both low and high voltage and how all of this is integrated into the frame and chassis. Coming from a diesel background I am a big “ground guy”. Start with checking the 3 main grounds. Battery to block, battery to inner fender and back of the P/S cylinder head to firewall. The PCM has multiple grounds on a stud on the upper intake manifold. Brown with a black tick mark IIRC.

If I get to “preachy” accept my apologies in advance. The next thing is check for “pending codes”. There are many protocols that manufacturers use regarding interfacing with the PCM. Since the advent of the OBDII protocol in 1996 it has gotten a bit easier. There is another protocol which is manufacturer specific. Year, make, model… Manufacturers have to have OBDII interface but then they have manufacturer specific codes too. A pending code is nothing more than the PCM has identified a problem but the problem hasnt risen to the point of triggering the CEL. Some pending codes require so many run cycles in order for them to set the CEL some are self clearing. This makes any sort of figuring this out a matter of luck… will you have the scan tool hooked up, will you be in a position where you can actually look at the data, a data logging scan tool is a big help, kind of tough to look at a scan tool while doing 65 mph on the freeway.

Each year manufacturers add more capability to the PCM, a scan tool can only check for what it can check for. For your make-model, is there a check for power to the fuel pump, no, is there a check for fuel pressure, no. This can be done by other means. I am a big fan of wiring in a 194 side marker socket and bulb to what ever electrical circuit I suspect might be having an issue and running it into the passenger compartment, driving around and when it acts up, look at the bulb. If I suspect that the fuel pump is shutting off while driving, wire it into the feed wire for the pump and at the same time have a fuel pressure gage plumbed in and have the gage taped to the outside of the windshield. If the light stays bright and the pressure gage drops when she stumbles, your pump is flaking out. If the light flickers and the pressure wavers, you more than likely have an electrical issue. The question now is it the fuel pump relay or the system that controls the fuel pump relay.

Unfortunately you are going to need some luck or wait until it is truly broken to figure out what is going on.

 

This is very helpful, thank you.

 

Well I'm back and the hesitation is even worse. It stumbles at like 15% throttle, driving slow or driving on the highway. It bucks like crazy. It's no longer limited to cold-only driving. All of the grounds are good, they've been cleaned and tested for resistance. I replaced my IAC as a shot in the dark wondering if it was misbehaving causing the bucking; I cleaned my already clean TB while I was in there. I got an Ultragauge to keep tabs on what's what. Long-term fuel trim is 0.00. 02 sensors are both bouncing between .850 and .100. When the bucking happens, there's no change in MAF reading. After swapping IAC and clearing the computer I got a pending P0450 code which took care of itself after about 15 minutes of driving. I'm back on coilpacks or injectors. Going to borrow my friend's coilpacks again while he's out of town next and try them for a few days to get a better sense if that is causing the issue. Still no codes or other pending codes. What should I look for on my scanner that may help solve this mystery?