We bought a used 2001 Grand Am (V6 automatic) a few months ago. Mileage was just under 100,000. It was running decently at first, but that improved once we did more maintenance. It’s gone from about 150 miles on the highway on a full tank to about 250. A lot of the problems didn’t reveal themselves until we took it onto the highways. These are the parts we changed in the last 2 months:
-new battery (old one was 0.1 above fail)
-all 6 spark plugs
-front oxygen sensor
-pcv valve and breather hose (old one melted)
-all 4 shocks/struts
Latest problem is OBD code P0301 cylinder #1 misfire. The entire car started to shake when we were in low speed in a drive thru. It only seems to shake in drive gear and it does it the whole time. It doesn’t shake in reverse or any other gear. Found out #1 spark plug was cracked and a chunk of the ceramic portion was missing. It got replaced but that didn’t fix the problem. Haven’t noticed any white exhaust yet. The ignition fails 1/7 of the time since P0301surfaced.
The last problem we had was P0420. We went to 3 different shops and nobody was able to fix the problem properly. It wasn’t until the pcv valve and breather hose were replaced that the code disappeared. The valve was actually cracked and parts of the breather hose were melted. I can’t understand why nobody noticed that.
I know there could be a lot going on, but I was hoping the possible problem could be narrowed down. Has anyone had similar problems?