Engine bucks only between 1800 and 2000 rpm - very strange problem

2006 Ford Escape XLT 3.0L DOHC - starts and idles fine. good power upto about 1800 rpm and then again above about 2100 rpm. Problem only exhibits under load (going up hill). Problem does not exhibit in low gears. No engine codes. Replaced TPS. Jumped out EGR to test it - still happened. I could be wrong, but I do not suspect fuel delivery or spark problems because the engine runs fine above 2100 rpm. So, basically I can start up a long hill and everything is fine until I get to about 40 mph (it’s an automatic, but I think it’s in third gear by now) then the car starts bucking (engine sputtering). But once I get through that, about 45 mph, it runs great - plenty of power, I can race it right upto 70 mph and beyond. What causes an engine to sputter only between 1800-2000 rpm and only under load? ANYBODY HAVE A GUESS?

Yeah do a fuel pressure test but I would also have the crankshaft sensor checked. On my Riv I would get a hesitation at speed under load. Replaced a lot of stuff but turned out to be the crank sensor.

Offhand, I might guess at an EGR system fault, intake vacuum leak, or intake tract air leak. Is there any history of the intake tract system being serviced or worked on before this problem surfaced?

A few years back my Lincoln suffered a problem that sounds similar to the one your vehicle has.
It would buck and jerk around 40 MPH only and would only do this during mild acceleration. Moderately hard acceleration or nailing it and there would be no problem at all throughout the entire RPM range.

I eventually determined this to be caused by a razor cut like split that had developed in a small, breather hose which had softened over the years and which took some digging to discover. During acceleration (and it varied) the hose would suck down and the split would open up. This in turn affected the MAF sensor as the split was located post-MAF and pre-throttle body. A piece of duct tape wrapped around it fixed it right up until the correct hose could be located.

Go to a local parts store and purchase an aerosol can of MAF sensor cleaner and clean the MAF sensor. The MAF sensor is one of the primary inputs into the computer. And if it’s dirty, it can cause the problem you describe.


I’ll bet my morning bagel that you have a fault code or two sittiing in your ECU waiting to be discovered. Many parts stores will read to for you for free.

This forum is awesome! Thanks guys. I plotted the MAF reading while driving (OBD scanner) it looked reasonable (about 3 g/s at idle to about 18 at 4000 rpm) but who knows. Cleaning it couldn’t hurt and cheap enough. I’ll try that next.

I’ve been tending toward the Crankshaft Position sensor also, but not the fuel pressure because it has plenty of power once I get past 2100 rmp. The next thing I’ll try after the MAF is breakdown and inspection of the intake between the MAF and the throttle body. I’ve been reading that can throw off MAF readings as well.

I’ll post my results. (1) clean MAF, (2) look for air intake leaks between MAF and TB, then (3) CPS. If I still have the problem, I’ll (4) check fuel pressure.

Thanks again.

PS: mountainbike, I’ll send you my address where you can send the bagel.

The bagel is in the mail.

I went looking to see if you had a variable valve timing system (apparently you do not) and found a link with some good info.

Are there any signs such as rattling or whirring that might suggest a worn timing chain or its tesnsioner?


This is a real head-scratcher. I really appreciate the help.

Update: getting nowhere so far… Cleaned the MAF sensor, cleaned throttle body, inspected and re-seated all air intake housings and connection points. Still no good.

No rattling or whirring. No whistling or odd noises of any kind. Still no engine codes.

Am I being stubborn not to suspect fuel pressure? It runs great once I get past the problem. Highway speeds - no problem. It can’t be fuel, right?

Is there a way to test the crank sensor? My understanding is if it’s bad the car won’t start. All tests I’ve seen are to see if it’s working at idle. Pretty sure mine is working at idle. What about my ECU – any chance I need a new (or reprogrammed) ECU? How would I test THAT?

I’ve had several fail total and you are dead in the water. However, prior to the one failing total, I would get the hickup under load at maybe 50-60 mph. No other symptoms for maybe 20-30K till it left me high and dry. Just my experience. I tried a lot of stuff looking for the problem including the trans. Don’t know about Ford but GM could also be a wobbly balancer throwing the sensor off.

The problem could still be caused by the MAF sensor. Sometimes cleaning helps and sometimes it does not.
It’s also possible that an intake vacuum leak could cause this and sometimes those leaks can be very difficult to find.

At this point and if the truck were mine, I’d connect a vacuum gauge to an intake manifold vacuum source and see what’s going on with the vacuum. This can also have an affect on the MAF.
If you do this it should be noted that vacuum readings will vary based on a number of factors but generally speaking you should see a reading of 17 to 20 inches with a rock steady needle.

It would seem to me that any problem with fuel pressure, crank sensor, and so on would show symptoms at RPMs outside that narrow range.
It is also possible for something like this to be caused due to a spark issue with a plug, coil, etc.

Weak spark and dirty MAF would be my first thoughts.
A compression test wouldn’t hurt.

Found it!!! Went to a remote area of interstate and ran it up to 90. She sputtered again, but this time – finally – threw a code. Misfire. Replaced the coil on plug and spark plug. All fixed.

Crazy that it only happened around 40-50 mph (no code) then again at 90 (misfire code). But, there you go.

This forum is really great. Thanks guys for the help.


Congratulations! And sincere thanks for the follow up post.

It never ceases to amaze me how often we overthink problems.

How did you figure out which coil and plug it was? I’m having same problem on my fusion (2018). I’ve changed plugs. Still have problem

If there’s a misfire code it will say which cylinder is misfiring, e.g. P0303 for cylinder 3, or P0300 for all cylinders misfiring randomly.