I have a 2003 Buick Lesabre Limited with 136,000. I had the car in the shop where they replaced the blower motor because the heat wasn't working. Two days after it left the shop the car started shaking really bad and it has a rough idle usually only when it'* stopped. If I'm driving down the highway with acceleration, it doesn't seem to shake at all, just when at a stop light or if the car is in park. The check engine light is not on and everything else is running smoothly. Car does not stall or make any noises other than the fact that it kind of sounds like an old volkswagen beetle. Usually the car accelerates fine unless I'm trying to go up a steep hill, then it takes awhile to get up the hill and it'* not normal. I took the car to an auto parts store where they ran a free diagnostics test. I had some error codes come up that read this

P0300 - Random Misfire Detected
P0140 - 02 Circuit No Activity Detected (Bank 1, Sensor 2)
P0141 - 02 Heater Circuit (Bank 1, Sensor 2)
P0300 - Random Misfire Detected
P0141 - 2 Heater Circuit (Bank 1, Sensor 2

The diagnostics also said the most likely solution based on common issues with this car is to replace the intake manifold/gasket.

Any help understanding this would be greatly appreciated.

Take and spray carb cleaner around the intake while the car is stumbling at idle and see if it smooths out. If so, then the intake gasket is bad.

It sounds like it'* missing on one or more cylinders. A small leak in an intake manifold gasket usually won't have this large of an effect suddenly. If you had said that it started a year ago and got progressively worse until today when it is like this . . . then I'd think more about the intake.

If it has no check engine light on while having any one of those codes (let alone all of them) then the bulb is out.

Intake manifold gasket is a big conclusion to jump to without knowing some more about the car.

When did it have spark plugs and wires replaced most recently (in miles and time)?

How long have you owned the car (in miles and time)?

Any trauma recently (body damage, driving through or parked in floods, etc.)?

I bought the car roughly a year ago. It was a two owner car and previous owner had been an elderly man who claimed to have taken super care of it, regular oil changes and kept up with repairs. The car was very clean when I got it and not a single light was on. Has run great up until a week ago when all this started. I have not replaced the spark plugs or wires but that was also something I had wondered. There is no damage that has been done to the car other then the giant ice chunk that fell off the passenger side tire well in the front. I took the car to a tire shop because I thought and hoped it was something more to do with the alignment but they said that everything looked great, all the parts looks good, they replaced a tierod but other than that, whatever was wrong with it I would have to take to an actual garage because they don't do engine repairs at the tire shop I brought it to. The mechanic at the tire shop said he didn't know much about it but he suggested perhaps a air control valve leak or a mass air flow sensor. I googled the symptoms and loose motor mounts came up also. I can now add that I do believe the car is using up gas more quickly. I haven't tried the carb cleaner spray as suggested above but I will try that first. The garage couldn't fit me in til Wednesday and I just wanted to get an idea of what could be wrong with it.

So there was no problem, until they installed a blower motor? That is accessed under the dash on the passenger side....not sure what they could possibly have touched to cause any problems......it'* a very simple job....3 screws....

The codes refer to a misfire, and a problem with the post catalytic converter O2 sensor, which is used to determine catalytic converter efficiency....it has nothing to do with fuel control....almost sounds like the O2 sensor is disconnected or cut....

As suggested check for a vac leak/exhaust leak.....misfire only appears at idle?

Turned out to be an ignition control module.

Well, at least you found the problem........

Unfortunately, this happens all the time.......car goes into a shop, and something else happens to a car, and the implication is that somehow the shop caused this.....

Thanks for letting us know how it turned out!

. . . and yeah, sometimes the second things breaks while fixing the first. The joys of machines.