Low RPM surging and stalling (1 Viewer)

[87warrior]

I just returned from a drive across Kansas and experienced an extreme surging RPM during the last 1/2 of the drive.

Traveling with a 2,500# trailer in 95°F temperature. Started the trip with gas from a station I always get fuel from. Hit the road at 65mph. Cruiser was running good, with transmission temperature between 150 and 175°F (checked via Torque Pro) but I did notice it was reluctant to upshift on several downhill and flat road surfaces. I discovered a quick click up on the cruise control "accelerate" knob followed by a quick click down would convince it to shift.

At 2 1/2 hrs into the trip we stopped for a quick break and to let the dogs run for 15 minutes. No new fuel at this stop (thank you LRA tank). Upon restarting the cruiser, I noticed some erratic idle and RPM surging. I tapped the throttle and it seemed to clear up. The next town was 20 mile down the road. As we come to a stop at the 4 stop lights in the next town, the Cruiser's RPM is surging between 300RPM and 1600RPM anytime the engine speed drops below 2k RPM. Throttle input had little to no effect on the surging and when trying to get going from a stop, throttle response was lethargic until the pedal was more than 1/2 way pressed.

Knowing this one-horse town wouldn't be able to help me or the Cruiser we pushed on since there was only one more stop sign between my current location and home (2 hours away). Cruiser ran great on the highway home, but the RPM's did try to surge when I slowed down for the last stop sign. When pulling into the driveway at home the RPM's only surged a little as I came to a stop. After unloading the trailer I tried to recreate the surging RPM at home and the darn thing was running great. It never threw a CEL, there are no stored or gray codes and none of the sensors I monitor when on the road seemed to miss a beat.

Not wanting this to reoccur when farther from home or on a technical trail, what should I look into for repair or prevention?

 

[87warrior]

I went all summer without another RPM surging issue until I went to Colorado in mid-September.

Once when driving through Salida the low RPM surging temporarily returned. It was 75°F. While driving, I shifted to neutral, turned the cruiser off and restarted it. The surging issue stopped. A week later I left a campsite near Carbondale and pulled to the side of the road to air my tires back up to highway pressure and let the cruiser idle while running the compressor. It was 40°F. When I was done airing up I hopped in the drivers seat and saw the tachometer jump around a little, then the cruiser died. I restarted it and did not have any issues the 13 hour drive home.

Now that I have returned home to Kansas the cruiser has had the low RPM surging every day I have driven to work (only in the morning after about 15 minutes of 2 lane highway driving). Temperature has been between 35° and 55°F. The RPM will bounce between 100RPM (or stall) and 1400RPM as I approach stop signs. The surging will stop if I restart the cruiser.

The CEL hasn't come on yet, but I now have a gray P0441 code [incorrect purge flow in the EVAP system]. This code may be unrelated and may have been triggered when I went over Hayden Pass again and had gas escape from the brand new gas cap again... (I have fought the fuel tank venting issue since I bought this thing 5 years ago). I have checked the purge lines from the canister and replaced two pieces that might have been leaking without fixing the surging RPM.

 

[lehiguy]

I have never had that happen on any Toyota, but I did have a TBI 350 (ok, that was in my FJ60) that did some of this. It was the throttle position sensor in that case. Yours may well be evap stuff as the evap system is barely adequate for the original tank and you have a LR tank.

 

[ramangain]

Since you have Torque, monitor TPS for a couple of weeks. See if it correlates to the RPM movement.

 

[87warrior]

@lehiguy and @ramangain I am happy to see you guys are thinking along the same line I am. I'll keep a close eye on the throttle position value in Torque to see if there are any irregularities. Is there a way to watch APPS values in Torque? I may have to fire up the netbook and watch Teachsteam for that.

My EVAP system is practically brand new and I haven't observed any more issues with the LRA tank than I did with the stock tank.

 

[ramangain]

Your throttle body butterfly doesn't stick I assume? No gunk buildup along the edges?

 

[87warrior]

Your throttle body butterfly doesn't stick I assume? No gunk buildup along the edges?

I haven't pulled the intake tube off in awhile, but I did clean the little bit of build up that was on the butterfly when I replaced the starter at the end of 2019. I will verify it is still clean.

Is there a way to test the electric motor that controls the butterfly? Maybe after 342k miles it has a bad spot like the brake booster... but if it was closing too far or not staying consistent the TPS should register those movements, right?

It stalled on me at lunch today as I was creeping around the drive-thru lane. I had Torque running and observed the throttle % stay at 13.7% during the slight surge then stall. 13.7-14.1% is what I usually see at idle.

 

[ClassyJalopy]

Have you ever had the Throttle Body replaced? I know there was an APPS issue that requires a new TB. Mine was replaced by the PO at a dealership.

 

[87warrior]

Throttle body and butterfly looked clean.

Have you ever had the Throttle Body replaced? I know there was an APPS issue that requires a new TB. Mine was replaced by the PO at a dealership.

Throttle body and sensors are original as far as I can tell. The service records do not indicate the TB was replaced by Toyota and I have not replaced it, the APPS or TPS. I just hate to throw $200-600 on sensors or the whole TB if don't know it is the issue.

 

[ramangain]

The next thing you can try and monitor is the engine load parameter in torque. I would imagine that if the engine load value is constant and the RPMs are bouncing around as you stated, that could be a clue as to what to start diagnosing next.

 

[87warrior]

Engine load is a display I have always monitored. I see a small increase in the engine load % when the RPM surges and I do no see an increase when the engine dies.

Yesterday I experienced the cruisers first [die, restart, die, restart, die, restart] sequence....twice. The first time was driving through the hardware store parking lot at a slow crawl. The next was with the Cruiser idling in the backyard as I was preparing to use it to jumpstart a Jeep project. When it died in the backyard I had the hood up and could hear a buzzing noise coming from the TB. I've never heard this buzzing before. I tried to capture this noise in video, you may need to turn up the volume to hear it.




There are now no codes stored, active or gray.

 

[ClassyJalopy]

This is certainly weird, almost sounds like an electric motor running constantly, could the throttle body motor be making that noise?

 

[white_lx]

See attached FSM inspection method for throttle body actuator (small motor), magnetic clutch and sensors. Time to pull out the multi-meter.

 

[87warrior]

I tested the TB sensors at 65°F today.

Throttle control motor: 12Ω [Spec 0.3-100Ω]
Throttle control motor clutch: 8Ω [Spec 4.2-5.2Ω]
Throttle position sensor: 687Ω [Spec 1.25-2.35 kΩ]
Accelerator pedal position sensor: 850Ω [Spec 1.64-3.28 kΩ]

The results seem to indicate tired TB sensors.

 

[ramangain]

The sensor wouldn't make that noise. The clutch sure would.

 

[white_lx]

The sensor wouldn't make that noise. The clutch sure would.

Correct. But if the sensors have unreliable output, the throttle motor could 'hunt' to find the correct positions which would be a varying target. It is very strange that 3 out of 4 resistance values are out of spec. Are you able to monitor the throttle position (Throttle POS) with a scanner (Techstream)? Not sure if the APS signal is also available.

Here is some more information about the throttle system (1st gen 'link' system):

ETCS-i / DBW System Troubleshooting - 2JZGARAGE

This article is to help out with the troubleshooting of the ETCS-i (Electronic Throttle Control System intelligence)also otherwise known as the DBW […]

www.2jzgarage.com

Edit: Thought about this a bit more. If you disonnect the motor/clutch connector, you can verify that the output of the sensors is OK with a multimeter by slowly moving the throttle cable side and monitoring the accelerator position sensor output. Next, move the throttle plate slowly and check the output of the throttle sensor. Both outputs should increase gradually / smoothly with no hick-ups in the full range (no dead-spots). There should also be no mechanical restrictions. If this all looks good the next step would be to check the motor/clutch.

Btw: The system has a limp mode. If you disconnect the sensor connectors, you should be able to drive with limited throttle. This could be a way to get home if this happens again.

 

[87warrior]

I decided to grab a used TB from the salvage yard from a 2000 Tundra with 140k miles. The throttle motor, clutch and TPS ohm'ed good. APPS had no continuity or ohm reading so I replaced it with my APPS. Started right up but soon the RPM dropped. When the low idle/ stall occurred I could see black smoke from the tail pipe indicating a really rich condition. The TB no longer makes that buzzing noise I posted above.

It idled fine with th MAF unplugged. Replaced the MAF and with the new sensor hooked up it still idled low and stalled.

I had a tip from a local cruiser head to clean the camshaft position sensor. I pulled it and it was definitely covered in 340k miles of goo. Cleaned and reinstalled. Cruiser did not stall while idling but it still struggled and would occasionally drop below 600 RPM.

I noticed when I shut the hood aggressively the idle changes. To me this indicates a loose.... something. When looking for a loose sensor I noticed the purge valve at the manifold has a broken clip on the plug. With the cruiser idling I removed the plug and noticed a distinct drop in RPM, yet no CEL was triggered. I need to do a bit more investigating as that did not make the cruiser stall as it had been doing.

 

[ramangain]

So the REAL hunt begins. It could be a multitude of little things combining to make a bigger event (stall).

Patience is a virtue!

 

[87warrior]

I tested both purge valves (one at the manifold and one at the canister) per the FSM. Continuity, Resistance, Voltage @ ECU and manually activating the valves by applying voltage to determine if they are opening and closing. They both checked out OK.

I checked (removed, cleaned with contact cleaner and reinstalled) the plugs on every sensor I could find: APPS, TPS, Throttle motor (I know its not a sensor), CPS, Camshaft Sensor, ECT, ECT (for gauge), MAF, 2 EVAP Purge, Vapor Pressure, and 4 O2. I did not access the Knock Sensor under the intake manifold, but the ignition timing seems to stay steady during the issue.

This morning I noticed the "Engine Load" slowly crept up to 100% as the engine started to stumble at low RPM. I also noticed the Short Term Fuel Trim pegged out at -20 (on both banks). The throttle seemed to be lethargic and surprisingly unresponsive while this occurred as well.

While I cannot locate any specific data points for Engine Load for Toyota, SAE J1979 specifies Engine Load Percent as:

LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) * (BARO/29.92) * SQRT(298/(AAT+273))]

Where:
- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO,
- SQRT = square root
- WOT = wide open throttle
- AAT = Ambient Air Temperature (in °C)

Characteristics of LOAD_PCT are:
- Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally
aspirated and boosted engines.
- Indicates percent of peak available torque.
- Linearly correlated with engine vacuum
- Often used to schedule power enrichment

If I understand the engine load data, it relies on the MAF (volume and air temp), ECT, TPS and Barometric pressure. What sensor calculates barometric pressure in the 100? We don't have a MAP sensor, right?

With the negative fuel trim, the ECU is decreasing the injector pulse to removing fuel from the extreme rich condition. Based on the research this is usually caused by a malfunctioning MAF sensor. The two MAF sensors I have tried both 'appear' to be working. I wonder if all of my injectors have gone bad (doubtful) or if its possible the fuel pressure regulator is not functioning correctly allowing too much fuel pressure at lower RPM thus pushing more fuel than expected through the injectors.

 

[ClassyJalopy]

I am impressed with your troubleshooting - hoping you will fix it soon!