I have a 1995 Pontiac Grand Prix se. I’ve noticed that ive been getting pretty bad gas mileage lately, and after driving my car for like 15 min, the engine light will come on, and my engine/transmission will shutter like its going over a roadstrip while its either downshifting or upshifting into 1st gear it seems. Then once I turn my car off, if I turn it back on the engine light will be gone (until I drive it for 10 minutes or so again), but it will still have the shutter. Any help on what this is? The fluids are full.Sorry I haven’t said more. The car has a little over 200,000 miles. It is the 4 speed auto tranny, 3.1 L v6. We had a newer engine put in about 50,000 miles ago. The tranny fluid looks good, and the oil looks OK, needs a change in about 400 miles. Been up to date on maintenance as far as tune ups, and fluid changes.
How many miles? What maintenance has been done so far? How do you check the transmission fluid? Please tell us more.
Reading out the applicable diagnostic codes would be where I’d start. There are probably some codes stored in memory even after the CEL goes out.
Lower gas mileage is often due to the engine not running at the correct coolant temperature, due to a faulty thermostat. The road strip sensation can be caused by a faulty lock-up torque converter. Your car has an automatic tranny, right?
Sorry I haven’t said more. The car has a little over 200,000 miles. It is the 4 speed auto tranny, 3.1 L v6. We had a newer engine put in about 50,000 miles ago. The tranny fluid looks good, and the oil looks OK, needs a change in about 400 miles. Been up to date on maintenance as far as tune ups, and fluid changes.
The very first things you need to do . . .
Pop the hood. Does the emissions label say “OBD2 compliant” or “OBDII compliant”
Look under the driver’s side dash for a D-shaped 16-pin data link connector
If your car is OBD2 compliant, you can get codes read for free at places like autozone, for example