Transmission Problem - '98 Lumina LS

My '98 Lumina exhibits what almost feels like a slight mis-fire at speed, when travelling along say at 50 mph at a steady rate and when I reach a slight grade. If I acclerate up the grade very gently it feels like a slight mis-fire; if I accelerate hard (and it downshifts) there is no missing.

An engine specialist checked it out and reported it wasn't an engine or electrical problem (no codes etc). He suspects it might be transmission/torque converter related.

A transmission specialist says he's not positive it is a transmission problem and would hate to charge me 10 hours labour (plus parts) to find out it wasn't the tranny!

Is anyone aware of similar problems with Lumina tranny's? Thanks.

PJ

Usually if it's a trans problem it would have set off the SES light but they did have some issues with the Pressure control solenoids and also I would pull the plug wires off the coil packs and look for corrosion. Very common problem on these, the coil tower will look rusted or burnt. They also had problems with the injectors plugging up a bit so a good fuel additive wouldn't be a bad idea either.

Usually if it's a trans problem it would have set off the SES light but they did have some issues with the Pressure control solenoids and also I would pull the plug wires off the coil packs and look for corrosion. Very common problem on these, the coil tower will look rusted or burnt. They also had problems with the injectors plugging up a bit so a good fuel additive wouldn't be a bad idea either.
I have a similar problem but I have a tach and noticed that the rpms were jumping up and down very rapidly in overdrive on slight hills. Now it's doing it on level ground when it's hot. (My wife initially told me about the problem she thought it was missing so I changed the fuel filter with no help.) Any way, my brother said to pull the pan to see if the transmission was shot by looking for brown residue in the pan. That was negative, so I'm in the process of seeing if anything is stored in the computer but didn't register a light. Let me know what you find out and I'll do the same.

your symptoms sounds like a sticky TCC solenoid. It's not unlocking the torque converter fast enough, causing the miss at cruising speed because the engine can't maintain speed at the rpm it is in, so it needs the TCC to unlock.

your symptoms sounds like a sticky TCC solenoid. It's not unlocking the torque converter fast enough, causing the miss at cruising speed because the engine can't maintain speed at the rpm it is in, so it needs the TCC to unlock.

You might be right, or there is a misfire, and it is causing the motor to rapidly change the load on the driveline right at lockup threshhold, making it jump in and out of lockup.