CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

2014 Ford fusion see 2.5l Rough startup

I was wondering if any car guys could give me a couple pointers here. I dropped a new motor in this car awhile ago and put about 1000 miles on it since with no issue.

Yesterday an issue popped up. After it cooled off and I started it again the RPMs started off normal then climbed up to 2k and hovered there for a bit then it started running terrible until I gave it has. I shut it off and had a roommate start the car while the airbox was open then as soon as the rough running started I clicked the airbox back together and the problem went away until it cooled off and was started again today. I know to clean the mass airflow and throttle body but if that doesn’t fix it where would I look next?

Is the check engine light on? If it is, what are the codes? If you can’t read the codes, tske it to the auto parts store and they will read it for free. Post the P1234 codes they give you.

For clarity the OP did not install a ‘New’ motor but a used one with 60000 miles supposedly .

Absent any diagnostic codes, it sort of sounds like the engine isn’t getting enough intake airflow for some reason. The parts that automatically open the throttle valve to adjust the idle rpm are all suspects. Your idea about the MAF and throttle body cleaning is good. Make sure there’s nothing blocking the path from the intake to the throttle body, and that it is completely air-tight.

Could be a problem in the ignition system too. Common heat affected parts are the crank position sensor, cam position sensor and ignition modules. Your car probably doesn’t use a separate ignition module, that’s integrated into the ECM, which is another possibility, but unlikely.

Fuel system problems could cause this as well. You’d need a fuel pressure test to know for sure. A fuel trim test (easier to do than a fuel pressure test) might show some clues though.

No check engine light and my bad about the new engine confusion, I was thinking it as more new to me. Didn’t occur to me that I should have said it was a used engine.

What all would I need to do a fuel pressure test or a fuel trim test and is it cheap to get the tools or should I just take it to a mechanic to have them done?

Also it didn’t do it again after yesterday afternoon so I haven’t really done anything yet besides cleaning. As far as I can tell MAF and throttle body are good and I don’t see any blockage. I will say the intake gaskets were still plyable when I took the intake off when I changed the head gasket so I reused them. I was informed yesterday that that may have been a mistake so I might try changing those as well if the issue pops up again.

Fuel trim testing requires a scan tool capable of doing that job. the less expensive versions don’t. That function requires “real time data” or sometimes this referred to as “mode 6” operation. If you haven’t done much diy car repair work on modern cars, I’d start with a fuel trim test done at your local shop. Make sure the shop has the proper scan tool of course.

Fuel pressure testing requires special equipment (albeit not overly expensive) and while many diy’er do it, fuel system testing can be somewhat dangerous. Not something for a newbie in other words.