Bali26

It sounds like vaccum leak to me. Use a carb cleaner to check by spraying it at where it might be leaking and listening for change in rpm.

MAF could be faulty. Check:

Don't worry about trac-off light, its just a symptom of the actual problem. You should just disable the trac by pulling the trac fuse out and try to fix whats making your engine run so bad.

I may be wrong about all this.

Lexushead

You should check those wires at night. Remove all the plastic covers and run the engine. Remove the cams covers as well for this test. My wire sparked between left wire and the cam back plate pointer thingy. Check for sparks jumping/grounding. I still think it's the wires.
You can also spray water over the wires(while the car is idling) and see if it kill (almost kill the car). I think the mechanic called it retarding the engine. If it does, it's the wires.
Injector o-rings are easy but takes time. I would just buy the head gasket kit if you decide to get the injector o-rings. It costed me more to buy just the o-rings then buying a kit from ebay. I bought a kit Item number: 220061255796 for $80.20 shipped because I was going to replace the valve cover gaskets and the oem valve gaskets cost almost as much for only the valves. I got the gasket kit last week and they "look" just as good as any other gaskets. I did a head gasket work on my Acura Legend with the oem gasket kits and this kit looks better. I'm cheap and what you decide to spend is up to you.

Devcon

Well I checked the vacuum, hooked up to a gauge and it has perfect vacuum, no leaks.

I checked the wires again, resistances are good. Didnt remove the valve cover, though.

MAF sensor tests out okay...

The idle cable was a bit loose so I tightened it a bit, its idling at 800-900 while in Drive and stopped, but in Park it shoots up to 1200 or so. Didnt think putting it in drive would drop idle so much...

It isnt the EGR system, as the valve works fine, and when it started hesitating/jerking I pulled over, yanked the vacuum to the EGR and drove off... No effect on the jerking... Reattached and no difference.

I also found one possibility, while working on the car, I had it in a heated garage, about 50-60F. It took a good long time for it to start 'misfiring' after it warmed up, but even then it was barely discernible. Yet, once I take the car outside (0 to 10F) it starts the hesitation jig... It is interesting to note that when I bought this car it was still Fall-like weather, fairly warm, and it had no hint of this hesitation/jerking issue. Now that the temperatures have dropped, its getting worse... Any sensors that could affect performance based on intake air temperature?

And still, when it sits overnight, it runs great when first started cold, but begins to 'misfire' and worsens as it warms up.

What the heck is going on with this thing???

PureDrifter

iTrader: (10)

how your timing?

are you positive the hesitation is a motor problem and not something with the trans?

Devcon

Positive it isnt transmission. The engine hesistates/stutters with the car in neutral, its just more noticeable in drive since the engine is now connected to the drivetrain.

As for the timing, I checked it with a light, and while idling it seemed to be pretty far advanced, but isnt there a procedure for checking the timing when in idle?

Then again, timing doesnt explain the erratic nature of the issue. How it works great when deeply cold and gets bad when it warms up... Or would it?

Devcon

I may have found the issue, or one component of it...

The engine starting jerking as it has been, fairly moderate this time. So I pull over, leave the engine running, pop the hood and start checking things...

Checked EGR, sensors, connections, nothing would change it. Then for the heck of it I took the MAF connector off, engine of course nearly died. I reattached the connector... and it ran perfectly! Several minutes later, it started acting up... So I did it again. And again it ran perfectly for a few minutes.

Now can someone confirm that all this means the MAF is giving faulty readings, so I can end this misery??? My two theories are:

1) The MAF is giving faulty readings. The engine disregards the MAF readings till it warms up? When it is unplugged, the computer pseudo-resets to a 'cold' mode and the MAF is ignored till it 'warms' up... Then it gets the faulty readings and runs rough.

2) The MAF being disconnected causes the computer to simply reset, like disconnecting the battery, putting the mixture to safe-defaults. Once the ECU recovers/relearns, whatever else is causing the issue continues causing it.

Now, I can get a remanufactured MAF sensor from Advance Auto for $262... I would rather not spend that kind of money on a sensor if it isnt really the problem. Ideas?

Sanpete

Since you tested the MAF and it was within specs, I'd lean to something like theory #2.

Can't remember--did you clean the MAF?

Devcon

I have not cleaned it yet as there is much conflicting information regarding that procedure on the forums. Some say yes, others no, that it is too fragile to clean, that cleaning causes damage, that its a temporary fix.

My confusion results from the diagnosis method conflicting with what I know of the operation of this type of MAF. The service manual indicates that it is an optical vortex sensor, but the diagnosis method checks for resistance... Is it heated-wire based or optical mirror based??? The resistance is fine, within normal spec as far as I can tell, but there are yet three other wires that I do not know how to test, and the fault could be on one of them. If I recall correctly, this MAF is also an intake air temperature sensor, which would seem to correlate to the checking resistance dependant on temperature. My worry is that the issue lies in the air flow metering...

Sanpete

Yes, that makes sense. It appears that the ohmmeter test only checks one aspect of operation, and that to test the rest you need to actually force air through the sensor and have a more sophisticated meter, and even then I'm not sure how telling the test is as to accuracy of the output. I'd call a Toyota or Lexus dealer and talk to a tech about whether they can test the MAF for you, and whether the test is all that useful. (You can also describe your symptoms and see what they suggest, of course.)

As for cleaning this kind of MAF (optical), I see your point there too. I suppose it's important that the air flow passages stay clear, some of which are small and could easily get plugged by dirty air, but I don't know how wise it is to try to clean it, as it seems it could easily makes things worse.

I still can't tell from your symptoms whether it is the MAF or not. Best advice from me: call a dealer or other trusted tech and ask. Can't hurt.

Devcon

I will be calling the closest Lexus dealership and see what they have to say.

I have read often that sometimes people unplug the MAF at idle and it runs great for them, even offering better performance at speed! This seems to be opposite. Unplug the MAF and the engine falls on its face, at idle. I would think though, that plugging it back in would immediately restore the symptoms, not run fine and then go bad after 4-5 minutes....

Devcon

Had a local dealership 'try' and do a diagnostic... But they didnt have the OBDI equipment. Figures. Didnt have to pay and they washed the car for me!

Anyways, they checked the thing over mechanically, and their diagnosis is a leaking/faulty fuel pressure regulator. I will be checking it over more thoroughly tomorrow and will let you all know what I find. I looked at the fuel pulsation dampener as well, and it looked like it was leaking a bit. Not sure if thats too serious, but it gets quite wet with fuel when running.

By the way, Toyota's TIS (techinfo.toyota.com) is well worth the money spent!

Devcon

Well I inspected the Fuel Pressure Regulator, and I think it is indeed bad. According to the service manual, disconnecting the vacuum line to the regulator would have an effect on the engine. Not this time!
With the vacuum line disconnected from the regulator the engine's running does nothing differently, even at varying throttles. I also notice fuel sputtering out of the vacuum line connector! This tells me the diaphragm inside the regulator is bust.
New regulator is on the way. Will update when it comes in and is installed.

Devcon

I'm losing my mind here.

Fuel pressure regulator arrived today and I sent about installing it, hoping it to fix my woes.

It didnt.

The car is STILL hesistating, jerking, losing power, dropping RPMs. This time I tried disconnecting MAF, but unlike before, with it disconnected the engine didnt die out. Upon reconnection, nothing happened. Now, with the MAF disconnected, revving the engine makes it die, with it plugged in it operates "properly", allowing power through revving. Also, disconnecting the vacuum line to the regulator had no effect. And yes, there is vacuum on that line!

Still the issue intensifies as the engine warms up. But now it no longer runs 'fine' when it is initially cold. It runs 'better', but still stutters. The problem just increases with engine temperature.

What on heaven or earth is causing this?

manli99

Wow!! you know a lot about car. I found a thread on.....

http://www.2carpros.com/topics/hesitates.htm

Devcon

Okay, another update. The new MAF didnt do squat. Still running rough. Does not matter what temperature it is. If it is in park or neutral, it isnt so bad, but thats because we increased the idle. I have ordered an oscilloscope to check over the electrical and ignition, to see if the issue is there. My two choices are:

1) Ignition. SOMEWHERE there might be a faulty connection?

2) Fuel. Injectors dirty/clogged/open/faulty? I do remember that when I changed the plugs a month ago, they were wet and smelled like gasoline... Could all the injectors be faulty? Remember, the fuel pressure regulator was bust, so it was putting out max pressure all the time. Would that have damaged all the injectors?

Also, the evil TRAC-OFF light has returned. And this time, when I jumper the connections to read the codes, the O/D OFF light starts blinking - but never pauses for digits! JUST like the TRAC-OFF light would do when I did diagnostics, it just kept blinking... And with the ignition on, engine not started, the light is off. But within 1-5 seconds of the engine running, it comes on.