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Rough running and coughing from idle to acceleration

Tiny
CRAIG POST
  • MEMBER
  • 1999 TOYOTA AVALON
  • 3.0L
  • 6 CYL
  • 2WD
  • 85,000 MILES
Have replaced; fuel injectors, fuel pump, fuel filter, air filter, PVC valve, spark plugs, plug wires, cam position sensor, all three ignition coils, all oxygen sensors. I have removed and cleaned the MAF sensor and the idle air solenoid valve. I have checked the codes with my code reader and have not gotten any. But I continue to have rough running and coughing from idle to acceleration. Seems to buck and surge when cruising at steady speed. Intermittent symptoms. Will easily rev to 6000 rpm's and have rocket-like acceleration after stumbling until about 2000 rpm's. I am going crazy trying to figure this out! Please help me!
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Monday, February 12th, 2018 AT 7:23 AM

18 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,912 POSTS
It sounds like the MAF sensor is out. Cleaning these only helps sometimes if they are too far gone they will not come back. Here is a guide to help other see what you must do to fix the problem.

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

Check out the diagrams (below).

Please let us know what happens.

Cheers, Ken
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Tuesday, February 13th, 2018 AT 11:12 AM
Tiny
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Are all of these symptoms consistent with this diagnosis? I am seeing other mechanics saying to check the IAC and TPS. Does the MAF sensor deteriorate slowly, or suddenly? The surging has been happening for quite a while, but the sluggish acceleration and coughing has been only recently.
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Tuesday, February 13th, 2018 AT 12:26 PM
Tiny
KEN L
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It goes bad slowly and than it gets to the point that is effects the engine. It kind of sounds like you have a camshaft lobe that is flat. I would do a compression test to see if the engine is okay so we are not throwing parts at a bad engine.

https://www.2carpros.com/articles/how-to-test-engine-compression

Take note of the spark plug color from each cylinder.

Also, if you can take a video of the problem and upload it that way I can see what is going on.

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Wednesday, February 14th, 2018 AT 10:06 AM
Tiny
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Not related to the problem
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Wednesday, February 14th, 2018 AT 11:31 AM
Tiny
KEN L
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Without driving the car it is tough to know what you are talking about that's why you need to be my eyes and ears a video really helps.
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Wednesday, February 14th, 2018 AT 11:33 AM
Tiny
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Compression check already done. No problem. All new plugs, coils, wires, O2 sensors, cam sensor, etc. Please reread my original posting. I might add that the car was my elderly mother's car, and sat for extended periods outside her home in Sarasota. Salt air? I'm shooting in the dark, very discouraged. Such a nice, low-milage car and I can't trust it for my wife to drive to work!
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Wednesday, February 14th, 2018 AT 11:34 AM
Tiny
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What do you mean by you need a video? While driving it? Under the hood? Showing the guages, or?
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Wednesday, February 14th, 2018 AT 11:37 AM
Tiny
KEN L
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I would like to see and hear when the car is having the problem. Without any codes it will be a bit of an investigation especially an intermittent problem. as you already know so as much information you can transfer to me the better a video is a great way to do that.

So this is what I see as on the plate so far. Crankshaft angle sensor, shorted injector or bad PCM.

We will figure it out. Please remove all injector connectors and check the ohms readings, they should be super close to one another.

Here is a guide.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Good times!
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Wednesday, February 14th, 2018 AT 12:34 PM
Tiny
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Thank you for your positive attitude. As you can probably tell, I need SOME good news! Tell me what kind of video you need, I'll do anything!(I'd even video my fish if that would be helpful)I'll ohm the coil packs and see what I get and let you know. But I think it's significant that the stumbling occurs only at the lower rpm's, and then it will suddenly accelerate like a rocket!
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Wednesday, February 14th, 2018 AT 5:16 PM
Tiny
KEN L
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Yep we will get to the bottom of it and when we do, nothing better. Use your phone to take the video and you can upload it here at the site in your reply. (Maybe a short fish video will help too :) and stumble or hesitation is indicative of engine timing of fuel mixture.

Did we try a MAF sensor?
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Wednesday, February 14th, 2018 AT 8:25 PM
Tiny
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I still need for you to tell me exactly what you want me to video. And, no, I haven't replaced the MAF sensor yet. Did I say that it also has new tires? New body is next.
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Thursday, February 15th, 2018 AT 12:25 PM
Tiny
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I replaced the MAF sensor with NO apparent change. I was hopeful when I discovered that the MAF sensor was not gasketed and I couldn't tighten it any further since it has shoulder bolts holding it in place. I tried sealing the old MAF with a gasket and a little sealant (silicone rubber). That didn't do anything. I then replaced the MAF with the gasket and that also made no difference. The car is running even worse, grey smoke when starting (not every time), hesitation, sputtering, coughing, surging. I'm at my wits end! Would you please tell me how to send you a video if you think that it would help.
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Thursday, February 22nd, 2018 AT 6:31 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
I would tend to agree with a MAF fault. MAF are sensitive components and specific to each engine. Did you get a correct replacement part?
If you have a scan tool you could try reading the TPS voltage to check if it is working smoothly when throttle is opened and closed.
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Thursday, February 22nd, 2018 AT 7:16 AM
Tiny
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I bought the exact duplicate replacement MAF sensor. What do you mean checking the sensor with a scan tool? The new sensor made no difference. The old sensor made no difference. I REALLY need some serious help here guys. Please tell me something.
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Thursday, February 22nd, 2018 AT 6:56 PM
Tiny
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I see now that you probably wanted me to check the TPS with a voltage meter. That's the only part on this car that I haven't checked or replaced yet. Wouldn't that be something if it was the whoLe reason for all this frustration? Just shoot me!
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Thursday, February 22nd, 2018 AT 6:57 PM
Tiny
KEN L
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With a video I can see how the engine is how the engine is stumbling. It almost sounds like you have a dirty throttle body have you cleaned it?

https://www.2carpros.com/articles/throttle-actuator-service

Please let us know what happens.

Cheers, Ken
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Thursday, February 22nd, 2018 AT 6:59 PM
Tiny
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Yes, when you read my initial posting, you will see everything that I have done. I will send a video later this morning.
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Friday, February 23rd, 2018 AT 6:08 AM

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