Engine Hesitation (All makes/models)

05camry33se

Thanks for your insights jbuchanan. It sounds like you are saying there are at least two probable causes for this problem (air mass unit or throttle position switch).

The TPS theory is intriguing because that's what it feels like when I'm driving, like my right foot's input is not registering for a while, like when I hit "enter" on my computer and nothing happens for a few seconds on the internet. Then, all of a sudden, ZOOOOOM!

I already know air mass units aren't cheap, how much would resetting the TPS (I assume this is a hardware part linked to a sending unit for the drive-by-wire) cost (ballpark)? Thanks

Chris

jbuchanan

Just a few thoughts,hope I can help.When you go to the dealer have you had someone ride with you and watch how you drive, then you can demonstrate when this problem occurs.that way someone at the dealer has experienced the problem and knows how to duplicate it.On these learning trans they shift differently with every driver,Try unhooking both battery cables and touch the cables togather away from battery this will drain all residuale power and erase the memory,then rehook battery and drive car hard lots of stop and go but get up to cruising speed do this several times the computer will think you drive this way all the time and set all the base settings and when you drive normal the computer bases the ignition timming and trans shift pattern and fuel injection on the enitial hard driving, sometimes you get better fuel milage.The early Jeeps has RAM.(random access memory) and every time the battery went dead you had to relearn the computer.Just a few thoughts for you,hope I could help.Good luck keep us posted.

jbuchanan

jbuchanan

Chris I'm not sure if this car is drive wire or has accelerator cable,need to know I had a problem with an Audi no dealer could fix had to reset the throttle housing motor and the throttle plate, It seems all manufactures getting alot of parts from the same place.can explain how to adjust tps if throttle is cable driven.

jbuchanan

jbuchanan

Chris, it was the same part number,2003 lexus suv and took the air mass sensor from a 2004 toyota van I think a sieanna,worked great,the lexus air mass sensor benched tested ok according to the alldata trouble shooting test I used.

jbuchanan

wwest

Thank about it, if the learning memory remained intact indefinitely how would the rental fleet be managed? How frustrated would an aggressive, leadfoot, get if they happened to rent a car driven the last 200 miles by a LOLITS, WA's Senator Murray for instance?

I'm willing to bet anyone good money that the driver's driving style learning system goes BRAIN DEAD each time the ignition is switched off. Now that isn't to say that other learning aspects aren't remembered long term, the idle air bypass solenoid parameters for instance.

jbuchanan tells us that switching a MAF seemed to cure the problem. If I'm not mistaken installing a new MAF requires a fuse or battery disconnect so the learning system doesn't continue to use the parameters learned for the old MAF.

regardless I wonder how the "fixed" SUV ran after a few days to "learn" the operational parameters of the Toyota MAF.

jbuchanan

Wwest I've been reading this forum for a couple of hours now don't see any suggestion from you,As to the Lexus,the customer called 2 weeks later to complament me for taking the time to figure out their problem when 2 different dealers and 3 independent shops failed to find and fix the problem,And if there was a problem with the way it ran after charging them good money to repair a problem nobody else could fix you bet they be rite back bit---- about the bill.
Just sharing info on an experience that I had sounds like it could have been related
Now if the car had to relearn every start up how poorly would it run and how long would it take to relearn for each driver?

jbuchanan

wwest

I did my best to say that's it's only the driver's "learned" driving style that MUST be forgotten prior to the next ignition restart.

I have found engineering "white papers" indicating, as an example, the system begins to "learn" your driving style the instance you put the vehicle in motion. Within 1 minute it has placed you in one of four categories. Within the next 2 minutes it refines it's "judgment" into one of sixteen categories.

To me it has become fairly clear that the engine/transaxle ECU is "experimenting" with the edges of the fuel/air mixture ratio total "map" to refine the parameters to obtain the absolute best in fuel economy.

In other words use the leanest fuel/air mixture possible, even below the detection range of the oxygen sensor, throughout the engine's RPM and loading range while avoiding engine knock/ping. That's going to make it extremely susceptible to engine knock/ping if you try to accelerate at low engine RPM, low torque, while also in an inappropreately higher gear ratio.

None of us have any trouble figuring out how the engine/transaxle ECU adjusts the timing if we fuel the vehicle up with an inappropreately low octane. The ECU detects engine pinging and adjusts the timing and/or the fuel/air mixtures accordingly.

But once we refuel with the proper octane, no knock or ping, how does it know to "reverse" those parameters it learned to use with the low octane.

It continuously "experiments" with the fuel/air mixture ratio.

If we could somehow prevent it from reaching mixture ratios so extreme as to cause knock/pinging then the "problem" would have a solution. Would a MAF sensor that indicates, to the ECU, intake airflow 20% below actual do this?

Maybe.

But now I begin to wonder if NOT clearing the memorized parameters for the previous MAF had a play in this drama? Maybe the new one is less accurate, overall, than the original, and always indicates, senses, less airflow than actual.

By how much would the new MAF have to be "off" in order to prevent the ECU from getting into the lean burn extremes. 5%, 20%....

bkinblk

In plain English (I'm not a mechanic), what can we do to eliminate the problem? Is the air mass meter something we can install? If so, how do you do it?

wwest

I have little doubt that if a new, even different vehicle's, MAF sensor is installed the proper procedure would be to pull the fuse or disconnect the battery in order to "wipe" the ECU's operational parameters learned during use of the previous MAF sensor.

Absent pulling the fuse the ECU will continue to use previously learned parameters based on the old MAF sensor. Which may be exactly what has happened here, all to the good.

In which case we might be able to accomplish the same "ends" without changing the MAF sensor at all. If we could somehow modify the MAF sensor's output signal, to be high or low(depending on which one works), above or below actual, disconnect the battery and let the ECU "learn" the mixture ratio parameter using this "false" signal, and then switch in the proper MAF sensor signals, that might do the job.

Remembering that if the battery should ever fail, or be disconnected, in the future we would need to repeat the false learning process.

user777

what about the angle of a faulty throttle position sensor?

wwest

Does the e-throttle system even use one?

The throttle positioning servomotor will have it's own dedicated position feedback device. Maybe even two since the gas pedal has redundant, dual, position sensors that are continuously cross checked against each other.

wwest

When you switched in the Toyota MAF sensor did you clear the ECU's previous memory?

wwest

According to the Rx330 04 shop manuals the TPS and the throttle position servomotor feedback sensor are/is one and the same. The shop manual indicate that the TPS is automatically "calibrated" by simply driving the vehicle.

05camry33se

"The shop manual indicate that the TPS is automatically "calibrated" by simply driving the vehicle"

So doesn't that coincide with the theory that the initial categorization of driving style might be involved here (by setting the TPS calibration)? If true, the downside is that one would have to drive aggressively for the first few minutes after starting out, which of course since the engine is not warmed up would waste a lot of gas, and probably isn't the best thing for the engine and drivetrain either.

05camry33se

That also might at least partially explain why some people don't notice hesitation/lurch. They may tend to drive aggressively right off the bat.

ecotrklvr

Just for the record - MAF's can be replaced, and often are. But they can be easily cleaned as well. I've cleaned mine, on several cars, and never NOT felt a smoother engine.

Search Edmunds Forums and/or Google for "MAF Clean", and see what you find. I've got one post in the mix myself.

bkinblk

Drove about 50 miles of mixed traffic conditions. MPG 21.7. Car does drive a bit better with less hesitation, but still is a bit sludgey (new word) from stop-first gear to second. Not real crisp upshifting and downshifting.

cam2003

About disconecting battery to erase "learned values", it only works for certain models only. Refer to TSB TC002-03: Engine/Transmission Controls - Resetting ECM Memory for listing all models.

Here is the copy of TSB

Reset Procedure 1

1. Connect the Toyota Diagnostic Tester to the vehicle.

2. Reset the ECM (PCM). Refer to the procedures below.

3. Start the engine and warm it up to normal operating temperatures before test-driving.

4. Perform a thorough test drive with several accelerations from a stop with "light throttle" application until proper transmission shifting is verified.


Reset Procedure 2

1. Disconnect the negative battery cable for 5 minutes.

2. Reconnect battery cable.

3. Start the engine and warm it up to normal operating temperatures before test-driving.

4. Perform a thorough test drive with several accelerations from a stop with "light throttle" application until proper transmission shifting is verified

wwest

The engine operational mapping parameters as shipped from the factory CANNOT be so aggressive as to possibly have engine pinging directly out of the factory. There are so many variations in all of the base engine parameters and sensors that the ECU must "learn" how to adjust the parameters on the fly.

Assuming the battery disconnect continues to work as it has so far the next would normally be to figure out how to disconnect only the engine/transaxle ECU to force it to revert to the more conservative factory parameters.

But now with the new of the MAF sensor swapping eliminating the engine hesitation symptom we need to rethink this approach.

I'm thinking that we cause the ECU to learn FALSE MAFS signals and then revert to actual MAFS signal without "informing" the ECU.

user777

somewhere along the way wwest, i stopped following....

would you post a link to the whitepaper on toyota's adaptive system if you have it please?

while we are talking MAF (Mass AirFlow) sensing, shouldn't we also be talking EGR (Exhaust Gas Recirculation) sensing as well? a poorly operating EGR valve can result in engine roughness, vague shifting, hesitation and stalling, can't it?

something from popular mechanics magazine:
http://www.popularmechanics.com/automotive/sub_care_sat/1272481.html

btw, when I was talking throttle position sensing, there are two places i was referring: the throttle body, and also the accelerator pedal. in a DBW system, wouldn't both have a position measurement device so it could be closed loop? my inclination, since the beginning is the root cause is there.

wwest

The Toyota system has two position sensors at the gas pedal for the relaibility of redundant systems. The output signals from the two sensor have offset voltages and are compared with each other for validity before the throttle servomotor "follows".

It seems that there is only one TPS but engine airflow can be used as a secondary feedback that the TPS is providing a "true" feedback.

wwest

At this moment I am not considering the MAF sensor as a cause, source, for the engine hesitation, just as a possible way to prevent the ECU from venturing into parametric areas that lead to engine knock or ping.

wwest

Where are you and what vehicle?

djman

i was just wondering if anyone would have any information on a Pontiac Grand Am 1993. Specifically engine hesitation, and misfiring. Im just wondering if there are any parts to just check-up or replace.

bkinblk

Drove about 75 miles today. Stop and go for about an hour and a half and 25 miles. The car shifts poorly in this situation. Accelerate to 10 mph, let off the gas, then reapply. This is where the car revs to 2000 rpm (like it's in nuetral), for about a second, then drops to 1000 rpm, "catches" gear, jerks, then moves forward. Try that for an hour and a half. However, overall, in all driving conditions, it drives a little better, but not enough to make me a satisfied owner. wwest: Do you want me to continue this test?

wwest

Carbon tracks inside the distributor cap, poor high voltage spark plug wires, spark plug gap too wide. Any of those can cause misfiring, ignite the mixture in the intake manifold, car stumbles until intake manifold is "refilled".

And lastly, burned intake valves.

bkinblk

Los Angeles area driving a 2005 V6 XLE Camry. 7700 miles.

wwest

Can you find the engine/transaxle ECU fuse?

It might be worth removing that and only erase the single ECU memory.

You seem to be saying that the engine no longer hesitates, revs (immediately?) to 2000 RPM, is that the case?

If so that confirms my suspicion that the engine hesitation, delay, is the result of the need to allow the transaxle clutches time to fully and firmly seat. The fact that it needs to downshift at all is to prevent the engine from lugging, knock/ping, in an inappropreately high gear ratio.

If anyone has a sequential shift and is experiencing the problem we could ask them to nudge the shifter down one time, one "toggle", each time the gas pedal is fully released. That would most likely prevent the coastdown upshift and thereby eliminate the hesitation the next time the gas pedal is depressed.

Anyone.....?

wwest

After sleeping/thinking about this overnight.

Now it begins to look as if the engine/transaxle ECU is actually LEARNING how long it takes the transaxle to downshift and is learning to keep the throttle closed for those learned durations.

Awaiting confirmation from bknblk, #1923, but in the meantime does everyone agree?

Pilot?

ecotrklvr

If you're willing to experiment a little more - try cleaning the MAF. Takes 5 minutes and costs about $10 for the electronics cleaner.

This might help the Grand Am as well.

ecotrklvr

You live in LA - I'm in Mission Viejo. If you ever want to take a ride this way, I've got the MAF cleaning stuff AND a generic OBD-II code scanner reset tool. If we can get together somewhere, we can do a quick read of codes, (reset any if appropriate - your call on that) and also clean the MAF.

bkinblk

That's a good idea. I'm in the Agoura Hills area. I'm not in OC anytime soon. Are you in the LA area anytime?

ecotrklvr

Not anytime soon - I figure you're about 100 miles away from here.

Next time I get to that part of the world, I'll message you here.

dla2

Someone should ask Bob Carter if they have fixed the hesitation problem for 2006 in the chat on September 29th.

05camry33se

...or maybe phrase it more like "Was the one second transmission delay designed into the 2006 models too?"

bkinblk

Drove about 60 miles today of mixed conditions. 21 MPG overall. The car is still indecisive from first to second gear and back again, sometimes hesitating in stop and go traffic. After slowing down to about 20 mpg, letting off the gas, then moderately stepping on iit again, the trans shifted up and down approx 3 different times until it found the right gear. I'm sure that is NORMAL.

bkinblk

Likewise- Appreciate the offer. I may take it to an independent close by. It shouldn't cost much.

jbuchanan

Mr.Wwest,sorry so late been real busy, I pulled of the sensor from the Lexus and read the part number off the old one to the parts guy at toyota,toyota can get almost any lexus part as long as you give them the correct part number.Yes I did clear the memory, I did not say this would fix the camry, this sounded like the same hes. that I experienced with the Lexus,and when I called about the part they literally stocked 20-30 maf sensors.And usually when a dealer stocks that many of one part there must be a real problem. The old sensor passed both bench test that alldata offered and did not set a fault code,so I went on a gut feeling and swaped sensors and it ran like a new truck,cust very happy, I've been a tech. for almost 25 years I dont claim to be the best just try to help out,I take it personally if i can't fix a vehicle or find the correct answer,by the way honda can get acura parts the same way but usually much cheaper,

jbuchanan

05camry33se

Do you have a theory as to why the swap was a fix?

Chris

jbuchanan

The scanner I have seems to have about 2-3 second delay on live readings,what do you expect for $3800.00 The only thing I can come up with is the values from the old sensor would change under driving conditions,I did not bench test new sensor to compare with old one, to excited that truck was fixed.I guess not much of a theory and not much of an answer.sorry.

jbuchanan

user777

right, it could still show a linearly increasing output as you apply the accelerator, but still be scaled low for the operational parameters or algorithms downstream in the ECU.

so - I wonder if someone with hesitation could swap out the MAF and see if it helps or not.

jbuchanan, with the scanner you've got, could you also perform a test on a vehicle and see if the accelerator when depressed linearly ramps up and down without a non-linearity? same with the throttle body position sensor?

$3800.00 - that sounds like one expensive scanner!

the $122 unit I pointed to which can read Toyota specific codes and capture real-time data to a laptop seems like a good value in comparison:

http://www.obd-2.com/
http://www.obd-2.com/toypida.htm

scoti1

bkinblk,

Read this, circa 2002:

cjts, "Toyota Camry" #4547, 16 Oct 2002 4:41 am

It sounds depressingly similar to your experience.

bkinblk

Depressingly similar indeed. However, this MAF issue is intriguing. BTY, I mailed copies of both arbitration results to the NHTSA along with a cover letter. The first stated my hesitation concern was "valid". The second result stated that a one second hesitation was "normal". Let's see if NHTSA agrees.

bkinblk

Whenever the memory of the ECU is erased, the vehicle will "run like a new truck (car), but only for a while. How do you know it was the new MAF sensor?

poto1x

From today's USA Today online edition

Note Toyota barely made the average, scoring lower than competitors such Nissan and Honda.

J.D. Power "APEAL" rankings This J.D. Power and Associates study is based on responses from more than 110,000 new-vehicle owners and measures what excites and delights them with their vehicle’s features and design. APEAL stands for "automotive performance, execution and layout."
Ranking is based on a 1,000-point scale
Porsche 908
Land Rover 906
Lexus 905
Jaguar 902
Mercedes-Benz 902
Infiniti 901
BMW 898
Hummer 897
Cadillac 896
Audi 895
Acura 886
Volvo 883
Mini 882
Lincoln 881
Nissan 863
Scion 862
GMC 860
Honda 859
Mercury 858
Saab 858
Toyota 857
INDUSTRY AVERAGE 855
Buick 854
Mazda 852
Mitsubishi 852
Pontiac 852
Chrysler 851
Isuzu 851
Ford 848
Volkswagen 848
Kia 845
Dodge 839
Chevrolet 838
Hyundai 836
Jeep 833
Subaru 830
Suzuki 828
Saturn 827
Source: J.D. Power and Associates

bkinblk

More of the same today. Drove about 30 miles. 21 MPG. Slow speeds and stop and go, the car is not nearly as responsive as cars I've had in the past, even with a fresh ECU memory (is it?)

bkinblk

Interesting Lexus is # 3, so I don't know if it can be attributed to dissatisfaction with the drivetrain.

poto1x

Agree with you, there is no information in the publication to explain the lexus/toyota diference, so we can only speculate.

Maybe when they pay $50K for a problem in a Lexus, owners are less likely to admit not being "delighted" than when they only pay $25K for the problem?

Or, maybe with a Lexus, they give you a chocolate chip cookie when they tell you to live with it because "they all do it".

05camry33se

Man, bkinblk, you definitely have some stick-to-itiveness...

Just thought I'd post up that once again I can make the 2 second delay happen at will...I think I was jabbing the accelerator too hard the last time I tried to replicate it.

By driving real slow like I'm about 90 years old I can make it happen no problem...and if I want to drive like a maniac, it NEVER happens..of course then the gas mileage and safety factor (in a different way, due to the fast driving) suffer...

So if you want to give it a spin Pilot, I do think I can get replication of the 2 second delay now. I sure feel sorry for any 90 year old who buys one of these...

wwest

Trying to find some consistency in inconsistency.

Are you saying that for some short period after you clear the memory the car shift normally?