I’ve got a '96 Sierra manual transmission with 215K that’s been running fine. I just ran it 400 miles without a problem. Recently I downshifted into fourth to go up a hill and I had a sudden loss of power and a rough ride like I had a flat tire. The harder I press the gas the rougher the ride and it idles almost normally. The check engine light came on and blinks 12 times.
Anyone have any ideas?
The blinking check engine light is probably a serious misfire (that’s usually what the blinking means). But there’s no point in spending much time guessing yet. Get the error codes read and post them - the format is “P1234” Most auto parts chains these days will read these codes for free. But don’t listen to what the parts store guys say about whatever codes come up. Just write them down.
When you come back with the codes report everything you have about the state of basic maintenance items - plugs, wires, filters at minimum.