We purchased a CPO 2011 Mercury Mariner Premium in October 2013. The first time this incident occurred was when we had the car about 2 hours. What happens is after driving for a while at a high-rate (usually about 60mph or higher), I gradually slow down as I get off of the freeway and start heading towards our house. Once I get into the subdivision, as I am coaxing, the car will lurch when it is at about 20mph. This also happens if I am on the toll road and then slow down to pay the toll then somewhere around there or when I stop for my turn, it will lurch. I took the car back to the dealer within the first week and the mechanic and I drove the car for a while and of course, it didn’t happen. He said there was no way for him to know what was happening unless it happened when he was in the car. I was actually put off because I asked if we should keep driving or take it back to the shop and he said “well, you know I don’t get paid for test drives”. seriously? lol
Anyway, they checked to see if there was an update on a module or something? He said there was (again, said he didn’t know if it was related to what I was experiencing). It is still happening. We previously had a 2009 Ford Escape and got pretty good gas mileage. That car was totaled (fortunately no one was injured…my newest teen driver lol), and we had hoped to get as good gas mileage with this Mariner but no. Also, in December (2 months after we got the car) the “check engine” light came one. I scheduled it for service for the following Monday (it was Friday) and later that day, the car kept dying. We had to have it towed in. They repaired that problem and we hoped that it would solve this other issue, but it did not.
There was a call to the show a week or two ago about a similar problem, lurching when slowing down or speeding up when driving at a low speed. The caller said she’d be coasting (in gear, foot off the gas) at 20 mph, for example approaching a stop light. Then say before she came to a stop the light changed green, so she’d barely apply the gas to speed up slightly, and the car would lurch forward. Likewise, at the same speed, if she barely had the gas pedal down just enough to keep from slowing down, then if she took her foot completely off the pedal the car, instead of gradually slowing, would slow down suddenly, with a jerk. Slowing to going around corners in neighborhood driving she experienced this same problem.
Tom and Ray said this was symptomatic of dirty fuel injectors. The injectors where not able to meter out a small amount of fuel, so when the ECM told them a little more gas was needed, they’d not put out a little, they’d put out a lot, causing a lurch. Likewise when a little less gas was needed, they’d switch to putting out none, causing a jerk-like slow down.
Tom and Ray suggested putting some fuel injector cleaner in the gas tank. Worth a try anyway. Another cause could be the throttle position sensor, so it might be a good idea to have that part tested next time you go to the shop.
There are a number of things a good shop can check if they’re willing. One is whether there are stored fault codes. Another is to test the fuel pump and fuel pressure regulator. Another is to put an analyzer on the engines and see what the ignition system is doing. In tough cases, and “event recorder” that records what the engine doing under operating conditions (while driving) can be used.
Fuel injector cleaner is definitely worth trying. It’s dirt cheap, easy to use, risk-free, and you might get lucky. But it always drives me nuts when a mechanic tells someone that there’s nothing they can do unless the vehicle malfunctions for them. Of course, you will have to be willing to pay for the diagnostic steps. Many people aren’t willing to.
Wow! you are all amazing! I will give the fuel injector cleaner a try and go from there. Thanks again!!!
We tried the fuel injector cleaner and it’s still happening. The dealer is not able to recreate the situation and is trying to tell us we have to pay for the diagnostics for a car that is Certified Pre-owned that acted up within 2 hours of purchasing it.
Drivability problems like this can be difficult to solve. Your car has a set of diagnostic software built into the engine computer, so hopefully the diagnostic trouble codes will show your mechanic the way to a quick solution. It could be other things, but I remain suspicious of the throttle position sensor. Best of luck.