2000 mercury sable being weird... HELP!

this is the weirdest thing. this first started happening about a year ago. started the car and it seemed fine put it in gear to drive stepped on the gas and there was no power. the car moved forward slowly and felt like the engine was skipping and catching and then it would die. took it to the shop and it started right up first try for them. they drove it and it was fine. ever since then it happens at random times on and off. im not sure if its bad fuel or something it just doesnt make sense to me. any and all help would greatly appreciated!

In order to even try to give you a good answer, we need to know…

…odometer mileage
…maintenance history (in detail) for at least the past 3 years. Statements like, “it has been well-maintained”, are essentially meaningless.
…whether the Check Engine Light is illuminated
…if the CEL is illuminated, have you checked for stored trouble codes?
…because this might actually be a transmission problem, rather than an engine problem, have you checked the trans fluid?

This is my girlfriends car and I’ve only known the car for a year so I’m not positive on all the maintenance. It has almost 90K on the odometer. The check engine light is not on and the transmission was replaced 2 years ago.

some people have said to put higher octane fuel in the tank to clean out the engine. would this work or is it just a myth?

It’s a myth, which is repeated endlessly by people who absolutely nothing about either cars or gasoline.

Getting back to, " I’ve only known the car for a year so I’m not positive on all the maintenance", unfortunately, unless you know (from hard copy documentation) that the required maintenance has been done–on schedule–you have to assume that none of it has been done.

So, my best suggestion at this point is to take out the Owner’s Manual, turn to the section dedicated to the Maintenance Schedule, take a look at the list of maintenance procedures for 90k, and have everything on that list done. Even if it doesn’t result in an immediate improvement in performance, this will make it easier to diagnose what does need to be done and will lead to better reliability in the long run.

Ya i was pretty sure that wasn’t true but multiple people have suggested that… but alright i guess we will have to make a check list of the maintenance done. thank you

Intermittent fuel pump pressure?

Do you have any reason to suspect you got a bad tank of gas? Or that your gas is contaminated by water or dirt? If not, I’d discount that idea.

Theres a host of things that can cause this symptom. Some minor, some major. When it happens on my Ford truck, it has usually turned out to be a vacuum leak problem. A minor problem in other words. A rubber hose has cracked or a vacuum device has sprung a leak. Asking a shop to do an intake manifold vacuum test will tell you one way or the other. If there’s a problem, it is usually fairly easy to figure out what hose or device is the cause. If this were my car, that’s where I’d start. Well, first thing I’d do before anything else is follow VDC’'s advise above, make sure all the own’er manual suggested routine maintenance is up to date.

My suggestion is to get the egr valve looked at. We recently had a similar problem with our 1997 Crown Vic.