Q: tranny mount or solenoid

asked by on June 10, 2016

Hello, I got a Nissan Altima 2004 , 2.5L. When I let off gas the rpm drops quickly to 1000 and jump to around 1200 and again drop back to 1000. Also the car jerks on acceleration and deceleration mainly from 1 to 2 or 2 to 1. It looks the transmission has delayed shifting ... My engine mounts were weak because when I was changing gear from P to R ro N to R the engine used to jerk, I replaced the (except tranny mount) but now after a month I think the mounts are loose again and engine moves a lot. Do you think the jerky shifting might be caused by a weak or broken tranny mount ? or it's the solenoid or valve body issue? there is NO light on. By the way, the jerky shifting is much more noticeable when I accelerate slowly, I don't feel a jerk if I push the gas pedal with high rpm and high acceleration

[URL="https://www.youtube.com/watch?v=03Sl9RpDM78"]https://www.youtube.com/watch?v=03Sl9RpDM78[/URL] Appreciate it if you can help me

My car has 147000 miles.
My car has an automatic transmission.

I watched your video and unfortunately it doesn’t give me the information I need. I do like the initiative though. In the future, which will be hard to record, I need to hear what the motor sounds like in the video. Ideally I could be there to experience all the little details that are difficult to relay in a video.

From your description it is difficult for me to know what direction to send you in. There are three distinct systems at play here. The transmission, the engine, and the engine mounts and/or transmission mounts. I will begin with the engine mounts. There have been reports that a rough idle like symptoms does occur as a result of worn engine or tranny mounts on your year make and model. So that is not necessarily the wrong avenue to follow. It’s important to note, it is often hard to determine if the motor is running rough or the mounts are just loose.

In most cases, if not always nowadays, if the motor is running rough there will be a Check Engine Light on. You didn’t seem to mention if that was the case, so I am going to assume it is not on. This is one step in a process of elimination. This doesn’t rule out the possibility that the motor will idle up and down without codes. Which is what appears to be happening from the video. What I can’t tell from the video is whether you are sitting in gear in your driveway or if this is at a stop while driving somewhere. There are many missing details here I could use to point you in the right direction. Is this on a cold start up, or after driving for awhile.

The best check for mounts is to power brake the car in drive and reverse while someone observes what the motor is doing under the hood. Power braking is the act of holding the car still with your foot firmly on the brake while you throttle the car. Doing this in drive and then reverse, the motor will twist one direction and then another. All motors will move under this situation. The question is how much. How much is too much is what we learn with experience, so this one may be hard for you to answer. You stated you had already changed mounts. It is possible they are faulty, but not likely. Did you change them all? You could have changed a mount that was causing the problem.

Mounts aside, the one thing that I would be focusing on after reviewing the information you have provided me is the hunting RPM’s. Is the motor actually revving up and down or is the tachometer just fluctuating on its own? These are two distinctly different problems. If the motor is actually fluctuating, you need to be checking for vacuum leaks and suspect the IAC (Idle Air Control) valve. If the tachometer is fluctuating without a corresponding RPM change from the motor, this could be a faulty instrument cluster or gauge. If the motor itself is fluctuating, then this should be the first thing to be diagnosed.

As for the jerking on acceleration, the best I can do from here is inform you of some pattern failures on your vehicle. Crankshaft position sensors are common failure items that can cause most of our symptoms. The crankshaft position sensors is one of the main sensors the PCM (Powertrain Control Module) uses to control both motor and transmission activities. If it is glitching out or has failed completely, this can cause a variety of strange symptoms. When I see odd symptoms, I am quickly suspecting such sensors.

The crankshaft position sensor is just the most common failure that fits your symptoms. There are several other possibilities that can create what you are experiencing. A throttle body main need to be cleaned and or a tune-up maybe due. Of course I haven’t addressed the transmission just yet. Your problem could certainly be in your transmission. A common failure on those transmissions is the TCC (Torque Converter Clutch) solenoid failing. When the torque converter goes in and out of what is known as "lock up", it will make the engine RPM jump as you described. The only problem I have with this possibility for your situation is the movie you posted doesn’t look like what I would expect from a solenoid failure. The issue is I don’t know the circumstances under which the RPM’s are fluctuating like that.

This is the best I can do when there are many questions that I would need answered. What really needs to happen next is some pinpoint tests. I would begin by observing scan tool data for any clues to what part of the system is problematic. With the exception of the engine mounts, there are many scenarios that can cause the symptoms you have described. If your up for the challenge and you have scan tool that can read PID data, then go for it. If not, then you are going to need have a technician take a look at it. This isn’t a simple diagnosis. If you would like to have this checked out by a professional, a technician from YourMechanic can come to your home or office to diagnose your shifting, idling, and acceleration issues.

Good luck. I hope I have helped you out.

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