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Engine hesitates while driving

Hi everyone,

My m=wife drives a Suzuki XL7 from 2007 with approximately 70000 miles on board. While driving the engine hesitates and the revs drop suddenly, not much but it is visible on the dash and the car shakes. I have changed the spark plugs, air filter is fine, and it is still doing it. I was thinking about changing the fuel filter however the filter is not serviceable in this car, it is part of the fuel pump assembly. A mechanic checked the fuel pressure and it appears it is fine. There are no warning light on the dash, no check engine light on and the car accelerates just fine if you give it gas. It has no problem starting and I have not noticed doing the same thing while idling, though this issue is intermittent. My wife stated that the problem happens regardless if the engine is cold or hot. Does anyone have any suggestions?

Cleaning the Mass Airflow Sensor (MAF) would probably be a good idea.

Thanks for your prompt response.
I looked at it however I cannot see any problems with it. I am not sure how to clean it because it is inside the plastic tube and cannot be pulled apart without the risk of breaking something. I do not see any dirt stuck on top of it, how would you recommend to clean it?

Leave the MAF sensor in the plastic tube and go buy some MAF cleaner. Take the tube off and spray it with the MAF sensor cleaner- and nothing else. Do not scrub it, touch it, or otherwise try to move it. MAF sensors are sensitive and it is easy to mess one up if you touch it or use the wrong fluid to try to clean it.

This site has a good how to on this:

The problem might be with the crankshaft position sensor.

If the computer loses the signal from this sensor for even a second, the computer no longer thinks the engine is rotating. The computer will then shut down the ignition and fuel systems.

The crankshaft position sensor also provides the signal to the tachometer.


In all likelihood you’ll save money by having a qualified shop do a diagnosis rather than throwing parts at the problem. An ignition analyzer, knowing what to look at (the condition of the fluids, for example) and some basic tests with things like a vacuum gage can go a very long way toward finding the source of the problem… and eliminating other possibilities. You can then decide whether you want to invest in the necessary repairs. Besides, even though your Check Engine Light isn’t illuminated, you could still have stored fault codes.

Find a reputable independently owned and operated shop and hire his expertise. It’ll prove to be an excellent investment. You can, if you choose, tell him not to proceed beyond a certain dollar limit to put a “cap” on your risk. No reputable shop will object to that, as long as it offers them enough to cover their diagnostic time.

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For this problem you need the basic diagnostic work-up that a shop would do. Let them tell you what’s wrong, then you can fix it yourself if you like.

If you want to go it alone, you’d need to provide some add’l info about which operating conditions this happens, and which conditions it doesn’t happen. RPM, vehicle speed, engine load, engine coolant temperature, weather conditions, etc.

If forced to make a stone-cold guess, most likely some kind of ignition system problem. You could have your battery and charging system assessed, that might provide a clue.

You need a mechanic to check information from the computer (through the the OBD port) during a test drive, while its malfunctioning, to get clues.

Well I took it to a shop and they told me most likely it is one of the cylinders misfiring. I did not leave the car for further tests as I will drive it more see if the computer will shows a code. I am also not sure about that because I do not get any warning or check engine light on. I was thinking for a while that it might be transmission because this happens only when driving usually right after starting the car in the morning or afternoon. We checked the oil and it is good. There is also a nasty noise that comes from the engine, could be transmission, not sure. All this is intermittent but when that noise starts the car starts shaking worse than usual giving the impression this might be related. The noise is hard to describe almost like 2 metal plates rubbing against each other. I agree, before trowing parts at it I should figure out exactly what is causing this problem. I will keep you posted once I get a solution.

If that noise sounds at all like shaking a can full of a dozen nickels, that can be caused by severe engine pinging. And it could also cause a shaking sensation. Intermittent engine pinging would likely be an ignition system problem. The crank sensor would be the first thing a shop would rule out probably. For a 2007, if there’s missing it would normally set a diagnostic code. If it was intermittent missing it might not turn on the CEL straight away, just store a code.

That’s nice, but you don’t know what further tests might have disclosed that would point you directly to the problem. You MIGHT get lucky, but you can’t count on luck to solve the problem; diagnosis has a much better chance.

George made an interesting point. If you have serious misfiring going on, especially preignition, you may be doing additional damage to the engine by continuing to drive it this way. I’d suggest that you let a shop do a full diagnosis.

You might have a timing chain problem. Your engine is known for premature failure. GM extended the warranty on their version of this engine for timing chain issues.