I have a 2001 Pontiac Sunfire. It's an automatic with a 2.2L engine. It's been a pretty reliable car for the last five years and 115,000m(I bought it used with 16,000m in 2002). I had to have the fuel pump replaced about 6 months after I bought it, but nothing other than wear and tear since then...until a few weeks ago.

Now, anytime I have less than 3/4 tank of gas and have spent any time driving (and I have a 40m commute to work), the engine starts to shudder anytime I am stopped at a light or stop sign. It also acts up when I am going up a hill or accelerating after stop and go traffic. It feels like it doesn't want to change gears. It hasn't stalled out on me yet, but I'm getting more and more afraid it will.

I took it into the shop last week. The mechanic changed the transmission fluid and filter, the fuel filter, and cleaned the throttle. He also "Sea Foamed" the intake and outtake (I think that's right...I am not up on all the lingo.) He said that after doing all of this, he drove it and couldn't get it to act up. However, the car had almost a full tank of gas at the time, and he didn't drive in the conditions I'm used to driving. I was hopeful that it was fixed, but I've learned that it still acts up if I have 3/4 of a tank or less.

I'm really at a loss here. I don't know if it's electrical, transmission related, or engine related. With my luck, it's all three. If anyone can offer some suggestions, I would be truly grateful. Thanks in advance.

I don't think it has anything to do with the transmission; mostly because of this statement?

Quote

When you’re sitting still idling in drive the transmission is not doing anything other them applying a light load on the engine. Look for things that can be affected by this load on the engine; spark plugs?

Dan.

Canadian "EH"