Low RPM surging and stalling (1 Viewer)

[87warrior]

Received a new MAF and Fuel pressure regulator from PartSouq. Tested the new MAF and it was right in spec at 2.43 kΩ at 68 degrees (inside my house).

I installed the MAF, started it and let the cruiser get up to operating temp. Fuel trims briefly went negative as it was warming up and RPM bounced, but did not stall. I then replaced the FPR and restarted the cruiser. It idled nicely and the fuel trims only stayed slightly negative (-6 max).

Data after MAF and FPR idling in garage.

I took it for a test drive and it stumbled a bit but never died. I had TechStream running in the passenger seat and only saw the -20.34 fuel trim once.

Took a gamble and drove the 100 to work today. I experienced some stumbling and hesitation between 2 and 3k RPM. Fuel trim for BANK 1 was -16.4 and BANK 2 was -6 according to Torque. It also died on me as I came to a stop sign, but the fuel trims looked more like they did in the TechStream screenshot above. It fired back up and continued down the road without issue.

Last night I noticed an option in TechsStream that allows you to temporarily tighten the parameters that trigger a CEL. I am going to activate that and go for a drive this weekend to see what happens.

What's next? Check ground points for sensors? Send fuel injectors to FIS? Remove intake and install new Knock Sensors? Replace Camshaft position sensor? Set it on fire and drive my wife's 200? <- (kidding, sort of... I really like the cooled seats!)

 

[87warrior]

I drove the 100 for about 150 miles this weekend trying to get some underload data recorded from Techstream while running the 'Check Mode' utility. Check Mode tightens the parameters that would trigger a CEL. It ran great on Saturday and all of the sensor data I observed looked good.

Attempting to make the best of this frustrating condition:

On Sunday it died while idling after driving to town. On the return trip home it stumbled some around 2k rpm @ 50mph, unfortunately Techstream was saving the previous portion of the drive's data so I did not get it recorded.

I went to the garage a couple of hours after returning home to check the ground points for the under hood sensors according to the EWD. The ground points were cleaned but I don't think they were corroded or dirty. I re-torqued the spark plugs and found all but one somewhat loose with no staining on the coil boots. Also used an unlit propane torch to search for vacuum leaks around the intake manifold and all hose connections but never did hear the classic increase in RPM indicated a leak was found.

As the engine was warming up I finally captured a slight RPM surge and subsequent stall in Techstream, the screen shots are below. Other than an extended injector pulse of 10.2 milliseconds and the rich condition that followed, I don't see much.

To recap the steps I have taken to try and solve this:
- Cleaned Crankshaft Position Sensor
- Cleaned Sensor electrical grounds as found in EWD
- Checked resistance of EVAP and Vapor Pressure VSV
- Checked that Pulse Damper screw pops up when running
- Checked that Air Filter was not plugged
- Checked and Retorqued Spark Plugs
- Checked for vacuum leaks with propane torch
- Checked sensors and plugs are secure and tight
- Checked Fuel pressure, found it was a little high
- Replaced Fuel Pressure Regulator with new Toyota
- Replaced TPS and Throttle Control motor with used parts that checked OK
- Replaced MAF with new Toyota
- Replaced EVAP VSV hose to the top of the throttle body with new Toyota

I've talked to a few non-Toyota vehicle enthusiasts about my cruisers problem, and more than once I've been told the ECU may be going bad. That is an expensive part to throw $$$ at if it doesn't fix it.

 

[ramangain]

Free diagnostic is to unplug your O2 sensors and see if the stumbling/stalling stops. You may want to see if you can get your ECU reflashed too. If errors occur during a reflash, then it could very well be your ECU on the fritz.

 

[jerryb]

rear bank 2 is always lean when the rest are rich in all screen shots above except number 1. even then both rears are lean in that one. Just an observation.
like he said. I would drive with both rears unplugged and watch or wait till a false knock safe mode. I would also swap in a new one and rotate around and watch the same volts.
in the whole thread no one said anything about what's your random misfire count?

 

[87warrior]

I will try unplugging the rear o2's to see if the stall/surge stops. I will also replace the rear o2 sensors. In the 100k miles I've had this vehicle, I have only replaced the B2S1 o2.

Free diagnostic is to unplug your O2 sensors and see if the stumbling/stalling stops. You may want to see if you can get your ECU reflashed too. If errors occur during a reflash, then it could very well be your ECU on the fritz.

I'll admit ignorance when it comes to flashing an ECU. Not many shops in the middle of Kansas do that kind of work. There is a local diesel shop that deletes modern trucks. You think they would have the equipment to reflash the 100's ECU?

in the whole thread no one said anything about what's your random misfire count?

Zero. I have the misfire counters for cylinder 1 thru 8 and the misfire RPM parameter running in techstream and they have never come off 0. If there is another misfire counter I am missing, let me know and I will pull it up.

 

[ramangain]

For reflashing the ECU, it may be wisest (certainly not cheapest) to have a dealershp do it through the OBD2 plug. Pay to put them on the hook. Last resort though IMHO

 

[ClassyJalopy]

For reflashing the ECU, it may be wisest (certainly not cheapest) to have a dealershp do it through the OBD2 plug. Pay to put them on the hook. Last resort though IMHO

@Mauser can flash ECUs, right?

 

[Mauser]

@Mauser can flash ECUs, right?

Yes, I can flash the immobilizer though. If the problem is the ecu in this case it is most likely a bad component or components on the board. It is vere rare that the programming would be bad.

I only have part number 89661-60610 for 98 and a few 99s. I can send you one to try. If it works you can buy the proper used ecu and I would be happy to flash it for free.

 

[jerryb]

I've never used techstream to watch misfires. It's always when I've been driving, usually under load, always on torque pro or OBD fusion.
I don't know where the random misfire count is in TS. In the phone apps it's at the end of the cylinder list for counts. OBD fusion it's in mode$6

seems like there should be misfires.

I haven't tried this approach to see total counts as in this video, but it is pretty informative and short.

 

[Eicca]

Have you tried any sort of fuel injector cleaner just for science? At this point, the stuff is cheap enough and it probably needs to be done anyway. I’d drain your tank down to the gas light, add a bottle of Redline SI-1 and fill it to just under halfway. Then give it the Italian tune up until the gas light comes on again.

I hold Redline SI-1 in high regard. My Lexus is running noticeably stronger and idling smoother after using it.

 

[87warrior]

I never have run a fuel injector cleaner, or any fuel tank additive, but do like to perform Italian inspired tune ups on the twisty highway by my house. Doesn't pump gas have a ton of additives today? I'm not opposed to dumping something in the tank, I just never have.

For the last week I have been driving around with O2 sensors unplugged.
- All 4 O2 sensors unplugged, it ran real rich (nose test). It was 80°F. I did not feel comfortable driving it and possibly ruining the cats.

- Replaced rear downstream with Denso 234-4154 and gasket. Plugged all 4 O2 Sensors in and it died on the way to work entering parking lot. Temperature was 55°F.

- Unplugged front upstream O2 sensors (rear downstream plugged in) and had been driving around for a few days. No dying no stalling no stumbling. Long term fuel trim for B1 stays at -3% but fluctuates between -4 and 0.8%, the long term fuel trim for B2 stays at -1.2% but fluctuates between -3 and 0.8%. Temperature has been about 65°F.

- This morning it died on the way to work entering parking lot. Still running with front upstream O2 unplugged and rear downstream plugged in. Temperature was 35°F and the fuel trims remained the same as above.

Should I replace Crankshaft position sensor and Camshaft position sensor?

 

[Eicca]

I never have run a fuel injector cleaner, or any fuel tank additive, but do like to perform Italian inspired tune ups on the twisty highway by my house. Doesn't pump gas have a ton of additives today? I'm not opposed to dumping something in the tank, I just never have.

I was always skeptical but my car is running noticeably better after two weeks of having that stuff in the tank. It's worth a shot. Redline SI-1 plus Italian tuneup. I call it the double-redline treatment.

If you fill up with top tier gas, you shouldn't have any issues, but still.

 

[ramangain]

You can try replacing those sensors, but the temporary working of your rig by changing the O2 situation seems like a hint to me.

Does Techstream report a reasonable value from your intake air sensor?

How do you feel about an ECU reflash?

 

[87warrior]

I mention the ambient air temperature since the issue seems worse as it gets cooler. When I unplugged the O2 sensors it was unseasonably warm for a week. Today was the first 'cool' day we've had in awhile...and it died.

The MAF reads the Intake Air temperature as well as the air volume. Intake Air temp and volume do not spike or drop. Their values seem consistent and normal.

I am not opposed to a ECU reflash. The closest Toyota dealer freaks out for any work that is not an oil change for a Camry so I am not sure how that conversation will go. My fear is it would be an expensive and time consuming exercise that won't fix the issue.

 

[87warrior]

I decided to throw caution to the wind and drive with all 4 o2 sensors unplugged.

- It seemed to drive well and somehow Torque was still registering long term fuel trims (my Techstream laptop battery was dead) around -2.5%.
- After 60 miles I pulled into the driveway and it sputtered and stalled. It started and stalled 6 times trying to get it into the garage.

With the o2 sensors unplugged the CEL is on. It is throwing 4 o2 codes and a P0125 “Insufficient Coolant Temperature for Closed Loop Fuel Control.” In a quick search it looks like this could be triggered by an upstream o2 sensor as well as the coolant temp sensor. I replaced my coolant temperature sensor 1 year ago when doing the starter since the plug had crumbled. Teachstream and Torque both show this sensor working.

I am getting an ECU from Mauser. The worse case scenario is I finally have more than 1 key and it doesn't fix the stalling.

 

[jerryb]

you say their values are consistent and normal. Are their voltages consistent bank to bank and front to front rear to rear.
I'd only be using fuel trim as a check against o2 voltages. If I was going to work backwards from the 02 sensors to the front intake air temp/maf/coolant/cam/crank I'd be sure I had good voltage reports related to trim/related to commanded AFR.
If you haven't set up to watch o2 voltage and trim #s with injector fuel cut and add in techstream, you should. I'ts informative.

 

[Eicca]

So I’ve been chasing ECU troubles myself on my 1998 1UZ lately. Intermittently the O2 sensors would simultaneously read low voltage and the thing would run like crap.

Long story short, my EFI fuse looked pretty discolored, and even though it tested good for continuity, I replaced it. I’m still apprehensive but my car is now running better than it has in over a year.

The symptoms could return any day, but it’s a cheap enough fix, and the universal rule is that computers absolutely hate low voltage. Makes them do all kinds of wacky stuff.

Give it a shot.

 

[87warrior]

@Eicca I will check out the EFI fuse and terminals in the fuse box, thanks for the suggestion. It certainly can't hurt while I wait for parts to arrive

 

[87warrior]

I received a 'new' ECU from Mauser, installed it and was able to quickly get my new keys registered to the ECU. Cruiser started up quickly @38°F and began warming up for the first time in 3 weeks.

It died while warming up. It also triggered a CEL, 2 MAF codes.

Replaced the 20amp EFI fuse as suggested. I didn't notice any corrosion on the fuse but put a fresh one in anyhow. It still stumbled and died.

Unplugged the MAF, restarted and it warmed up to operating temperature no problem. I tested the MAF again, and the values were still in spec per the FSM. I tested 2 of my other used MAF's I hadn't throw out and they test just out of spec, but tried them (for science) anyhow. The Cruiser would continually stumble and die with any MAF plugged in.

I studied the EWD and noticed the MAF is wired directly to the ECU through a junction behind the glovebox. I suspect there could be rodent damage or a pinched wire along the passenger fender well where the wiring runs under the hood. Removed my ARB compressor and dual battery tray and inspect the wiring noting no damage. Moving inside I have a hard time tracing the wires once through the firewall and in the dash, but the factory harness looked undamaged inside.

After fiddling with the wiring I start it up and it idles fine. To test continuity at the ECU, I haphazardly push on each wire bundle that is plugged into the ECU. I quickly realized by gently pressing on bundle (B), the vehicle will die. Incidentally this is where the MAF wires connect to the ECU. If you turn the volume up you can hear it idle then die.


I further isolate the wire responsible for the stalling to this green/white wire, which is a MAF wire. I am able to kill the engine many times by every so lightly wiggling this wire.

I pull the wire out of the connector and squeeze the female connector together and reinstall.

3 days later it hasn't died (yet), but my mind keeps picking up on phantom stalls since stalling has become the norm for this vehicle. I am NOT saying it is fixed until I get more seat time. However, it is my speculation that this loose MAF wire to the ECU could have been making poor contact with the pin on the ECU resulting in erroneous MAF readings and it could have been happening so fast the ECU wasn't reporting it as a problem and Techstream was struggling to display it.

 

[KillerBox]

Thank you for reporting back and if it was my suv, I would disconnect the wire and spray some DeOxit 5% on it.

It is a mild cleaner and protectant made for wires. You can order it on Amazon or you might find it locally at a guitar type of shop.