I don't get it, the car is a 95 formula, high mileage, 190,000 miles...

I have replaced everything on the car once or twice but has been a while since any ignition parts were done, I think I did plugs/wires on it at 100k , coil and module too, optispark was changed little over 100k too (actually due to misdiagnosed problem) so I gues all of these could use to be replaced again but if someone can tell me how to diagnose this maybe i don't have to waste all the time

engine runs ok at most rpms and speeds , not perfect but without any real stumbling/shaking, this shaking/stumbling only shows up between 45mph and 55mph around 1250rpms , for example if I feel the shaking come on I can give it a bit more gas to rev to 1500-1700rpms and it's fine , so just very light throttle at those speeds will do it.

it feels like a misfire on 1 or more cylinders, I am just surprised it's not present all the time so I have a hard time blaming coil/module/plugs/wires, but I could be wrong... doesn't sound like opti going bad either does it? no check engine codes, I have TTS Datamaster cable & software so I plan on recording this mess , I Just have to find a laptop with serial port & good battery, lol

any ideas?

TIA for any help , I'm hoping to nurse the car to 200k on original motor before I blow it to pieces

 

I have the exace same problem as you so I will be watching your thread. Mine will stumble at low speeds around 2000 RPM / 25-45 MPH, give it a little throttle and it comes right out of it, idles and runs good at WOT. I changed my plugs recently and it is a little better, wires coil and opti have about 10K on them. My next step is replacing the 45K mile bosch O2s with some AC delcos.

 

Do an ignition tune up and go from there.

 

An ignition miss is most often felt at low RPMs in a tall gear. It may seem to go away when downshifted or RPMs go up and load goes down.

 

Sounds to me like you are lugging the engine. That RPM is close to idle. JMHO

 

1250rpm should still run smooth, although I wouldn't cruise at that low of an RPM just because it's lugging a tad.

 

Assuming that it is actually 1250---since the tachs usually read around 250 high. JMHO

 

Possible dirty injector. I would run some cleaner thru them. Either that or an ignition problem...JMHO

 

I wish that was it, lol, this formula has very low rear end gears, the lowest offered for that year (ratio escapes me at the moment).

it has been flawless for 130,000 miles that I've put on it and makes and awesome cruiser

 

I'll start throwing ignition parts at it and will post results thanks

 

motor mount(s)????

 

I;ve got the same problem, it lessened a bit since I changed out the plug wires, but I'll be watching this thread as well

 

well I did the coil - didn't help
then I went on a buying spree , replaced module , dr. side plugs and wires and problem is gone.

granted now I have one side with 100k on plugs and the other side with 0 , lol, but I'll do the passenger side plugs next weekend, as you all know it's a ***** to do and I usually end up pulling the exhaust/starter/alternator out of the way

 

Torque converter will lock up at part-throttle around 42-45mph with the stock tune.
Some converters (Yank specifically) engage very hard and cause vibrations at that speed when at part throttle.

 

I really wish I had seen this a few weeks ago...I had the same problem for a little bit... now it idles rough and even takes off rough. The only time it runs smooth is when I have the pedal against the floorboard >.< (not that I do that just to get it to run smooth...) I am going to have to bite the bullet and do the plugs...assuming that it's the problem...