Vibration at various speed/gear changes

[NJ727]

Hello, so before I start here is the background of my Reatta for context of how she's been handled and her general condition;

 

It is a 1990 Reatta (Base model, no additional features) that's rust free and has been a garage queen her whole life, for the last 25 years or so she has been just a summer car for about 3 owners, with her original owner putting 65000 miles on her from 1990-1993. Her maintenance records are foggy and really can only be dated back to 2016 as the previous owner passed away.  Her current mileage is 78000 miles and some change, with signs of front end work being required such as new struts, shocks and an alignment with a clearly failing BCM (Trip Computer stopped resetting, doors half way lock and unlock, sometimes randomly). When I first purchased her there was no vibration, but as I've been daily driving the idle when stopped in traffic tends to become sporadic resulting in unwanted vibration, which can be resolved when going into neutral. In addition at about 40mph when in OverDrive the car begins vibrating when lightly touching accelerator. To resolve this vibration I let go of the gas, then use much more force, which allows me to gain speed without vibration until shortly after. Letting go of the gas acts almost like a clutch, with the faster your going giving you less and less time of that no vibration period. Below 40mph and in Drive she is fine with only minor vibration when approaching 50mph (Which to my knowledge the car should simply be in OverDrive at that point). 

 

 

Now my current problem;

 

After researching my symptoms I was suggested cleaning the idle air control module, and replacing the spark plugs. This weekend I did both tasks and her vibration during idle was relatively fixed. I admit I could of cleaned the IAC module better but the vibration when sitting in traffic while in Drive has been significantly reduced. The sparkplugs have also helped restore some lost power, improved my gas mileage and fixed some vibration. The sparkplugs I replaced however may be original, as they were rusted on the exterior and clearly from another decade ( I have photos if truly interested ). The engine ultimately sounds better and is definitely running better, BUT the vibration is still present!

 

Vibration now occurs around the 45-55mph mark when in OverDrive and in Drive, although now I can achieve highway speeds without too much hassle it still is a problem. This vibration also occurs during sudden acceleration, usually done when merging on the highway. So my question for the forums is just what else should I do? Would a transmission flush be appropriate? Is there any sensors that may be causing the issue? Again I believe most of the parts and fluids are original, although cared for, age and time has definitely taken a natural toll on various parts, such as the headlight arms that need replacement and some simple interior features that rely of glue needing more adhesive.

 

This upcoming weekend I intend on replacing the Serpentine belt and the 02 Sensor, I have an 02 sensor from a 1987 Buick Grand National and it appears to be an exact fit (If its not let me know)

 

 

 

[Ronnie]

50 minutes ago, NJ727 said:

Vibration now occurs around the 45-55mph mark when in OverDrive and in Drive,

Classic signs that the ignition system is breaking down under heavy load at low RPM. Most likely bad spark plug wires but it could also be a problem with the coils or ignition control module. As soon as the transmission downshifts and/or the torque converter unlocks it takes some of the load off the engine and it smooths out.

[NJ727]

ICM coming in tomorrow along with some new sparkplug wires. Also going to get a new crankshaft sensor while im at it. Ill update on the progress of the cars condition. 

[Ronnie]

I would do the plug wires, then the ICM, and see how each one effects the problem you are having. Save the crankshaft sensor until you have got it running with the new ICM and wires. Changing everything at once can be a nightmare if for some reason it runs worse, or won't run at all, and you have to start troubleshooting it. 

[NJ727]

I replaced the ICM and coil pack, engine sounds much happier but vibration is still present. I would also like to add that during these vibrations my headlights flicker, my Climate Control panel flickers, my idiot lights flicker, and my gear indicator (Thing that shows drive, neutral, park, cant think of the right name to save my life) also lightly flickers. My cluster board however does not flicker. I will get the tranny flushed this or next week and may look into a crankshaft sensor replacement. 

[Ronnie]

On 11/19/2023 at 9:44 PM, Ronnie said:

I would do the plug wires, then the ICM,

Why did you skip over the spark plug wires. I've found that to be the most likely cause of the symptoms you described.

[NJ727]

Sorry, I did change those as well, just totally forgot to put it in there, my bad

 

[ship]

Apologizes for going off topic NJ727, but where in MA are you located?  I'm in Weymouth.

[NJ727]

2 hours ago, ship said:

Apologizes for going off topic NJ727, but where in MA are you located?  I'm in Weymouth.

Im in the Dartmouth Area myself