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Deceleration

My 2006 Toyota Corolla will suddenly decelerate for a period of 3 to 5 seconds. No warning lights come on and the engine does not cut out. This has been happening sporadically for about 2 years. It will occur 2 ot 3 times in a day of driving. The dealership says they cannot diagnose the problem since they can’t duplicate it. The ECM was replaced several months ago. The car has 120000 miles on it. Any ideas? I just got a new battery and transmission fluid.

The ECM was replaced several months ago. Why was it replaced?

Need more information:

Does the engine rev higher but the car does not accelerate? Is it automatic or manual? Does it occur while you are accelerating or cruising at speed?

Are you using cruise control or not?

What color and level is the transmission fluid? Does it smell burnt?

Maintenance up to date? (air filter, spark plugs, wires, etc. should have been replaced at least once in 120K)

Engine does not rev higher. Automatic. Occurs while cruising at speed. Just had transmission fluid replaced today. Deceleration happened 3 times after that. Maintenance is up to date…at 99, 000 miles spark plugs etc. replaced.

ECM was replaced because of recall.

I know that people are fond of claiming that Toyota’s electronic throttle control issues were “proven” to be non-existent, and that cases of unintended acceleration were all operator error. But there is no way to “prove” that, and I don’t buy the operator error claim anyway. Those things have problems, and I’m betting you are having electronic throttle control issues. All I can say is to feel lucky that you are having sporadic “unintended DEceleration” issues.

Fortunately the car has not decelerated in heavy traffic with another car on my bumper because that could cause a serious accident. So the electronic throttle controls acceleration as well as deceleration?

Do you have an Tachometer on this car? And does it go to zero when you decelerate… I guess what I am asking is does the motor feel like it shuts off, and then comes back to life on its own??

The motor does not shut off…tach does not go to zero. It feels like gas stops flowing for a few seconds.

In that case I would get a fuel pressure gaguge on this car and drive it around. If it is happening this often it should not take long for it to act up, you need to know what is going on with the fuel supply. If its ok, then you may just have a loose wire on the ignition somewhere…

Anyone know for certain whether a 2006 Corolla has an electronic or cable-actuated throttle? Media firestorm was over the Camry, Lexus SUV, and Prius as I recall. Weren’t all problems proven to be driver error or attempts at fraud?

Termite–do you know what the transmission fluid looked like before it was changed? Is this the first time it was changed?

You say the tach does not go to zero. Does it drop suddenly then resume speed?

If it were the gas pedal position sensor the check engine light would come on.
If it should happen when no other cars are around try immediately shifting the trans into neutral and see if the engine stalls.

“If it were the gas pedal position sensor the check engine light would come on.”

That’s not necessarily true at all. Plenty of things can misbehave without going outside of normal specs. If it stays within what could be normal the computer doesn’t know the difference.

They said the transmission fluid was black. I believe it’s the first change. The Tach drops a bit when it decelerates. The problem continued today after the transmission fluid change and a new battery.

Suggest to double check spark plug condition and that gap is correct and air filter condition is good. Spark plug gap increases about 0.001 inch per 1500 miles due to electrode wear. A too wide gap can cause this, as could a plugged air filter. A plugged fuel filter could also, but less likely. There’s an off-chance it could be a brake problem too. A sticking caliper or collapsed brake hose.

If it isn’t any of those things, which are fairly easy to check, you’re gonna need to get an experienced Toyota expert on you team & under the hood. Someone with the correct test equipment and experience fixing Toyota engine problems, includingToyota fuel injection and emissions equipment. Solving this may take some time doing a series of trial and error experiments.

"They said the transmission fluid was black. I believe it’s the first change. The Tach drops a bit when it decelerates. "

Now it sounds like a slipping transmission.