Rough idle, stalling, P1133 and P0305 [Archive] - Forum


View Full Version : Rough idle, stalling, P1133 and P0305

10-15-2013, 06:36 PM
For the past week or so, my 2002 grand am has been idling rough. Recently, for the past few days I need to rev up the engine once I start it for a few minutes, otherwise the engine will stall out. I have had the P1133 and P0305 codes show up when I test it. My question is, would a faulty O2 sensor cause all these problems, or does it sound like something else?

10-15-2013, 06:40 PM
that sensor (in conjunction with a couple others) helps the engine determine how rich or how lean it needs to run, so it could very well be off so far you have to keep your foot in it to keep fuel flowing, or to keep air into a rich condition.

10-16-2013, 12:44 AM
I would definitely start with the upstream O2 sensor, its fairly easy to replace, and it should clear the P1133 code. The P0305 is a misfire on Cyl 5, which is possible if the O2 sensor is throwing the fuel trims too far out of range, but I would expect if it was only the O2 sensor causing the issue, that the misfire would move around. So I would check the spark plug in Cylinder 5 (really I'd probably check all of them) and make sure the plugs all look similar. It could also be the plug wire to Cyl #5.


O2 sensor - Replace
Plugs - Check/Replace
Plug Wires - Check/Replace

10-16-2013, 04:13 PM
Thank you for the replies! I just bought the upstream o2 sensor and scheduled an appointment for Saturday morning. Is it necessary to replace these sensors in pairs, or should one new one do the trick and fix this issue?

10-16-2013, 05:33 PM
Usually the Upstream one goes bad first since its before the catalytic converter and is doing the brunt of the work. The downstream one will go bad also, but it takes longer for the downstream one to fail typically to the point it causes major problems. The downstream one primarily monitors the Catalytic converter and doesn't need to be as fast to respond. The upstream sensor has to be fast and accurate to provide the best performance.

I replaced my Upstream O2 about 2 years ago, and it made quite a difference in how the car ran. Since then I've gotten a OBDII reader which lets me monitor and log quite a few of the sensors in the car, and have noticed that my downstream sensor rarely moves around voltage wise. I am getting fuel trims which are outside the +/- 5% range mostly at idle, so I've got one of Milzys Catted downpipes on the way, and I plan to replace the stock Cat and the Downstream O2 at the same time to improve the performance and to hopefully get the fuel trims back in line. With 187k on the O2 sensor and stock Cat...both are probably starting to get tired...15 years isn't too bad.

My upstream O2 voltage is will bounce from high to low voltage pretty regularly and pretty fast when I change the throttle, both under load and while cruising. But the downstream O2 sensor typically stays around one particular volt reading until I change throttle significantly, and then it will settle at a different reading for a while. From everything I can find, the downstream O2 sensor should be fluctuating high to low to high, just much less frequently in relation to the upstream O2.

Let us know what happens after the upstream O2 is swapped should see an improvement. And give the plugs/wires an inspection at the least, especially on Cylinder #5.

10-16-2013, 09:13 PM
I had a very similar probably where I would have to press the gas right as it started and rev the engine for a while then drop it into reverse and hope it wouldn't stall and it ran like crap when it did run. I don't recall ever having any check engine lights on at the time or if there were any codes. It ended up being carbon build up where the iac sensor mounted after cleaning it, it ran like a champ and haven't had any issues to this day.

10-21-2013, 11:40 AM
I had the O2 sensor replaced this past weekend. It definitely seems to run better than it did before. It now idles high for a little while before the rpms lower. My question is, is this normal, or does it take a few trips in the car for the 02 sensor and computer to fully be adjusted and in sync?