Q: My car jerks slightly when I'm at a steady speed or trying to stay at a constant speed only around 40mph to 50 mph

asked by on August 26, 2016

when I try to stay at 40 45 mph my car chugs jerks slightly, but when I hit the gas it goes away only usually at those speeds. I replaced spark plugs all but number 3 today didn't change anything, change tps nothin, changed air tempature sensor and no change. I am running out of ideas also when I hit the gas hard I get black smoke. Took it to auto zone to get a diagnosis and the Egr code came up as well as fuel system lean... please help

My car has 163000 miles.
My car has an automatic transmission.

In the future, please include the codes as they can help use pinpoint and give you a more accurate answer.

The surging you feel while under light throttle, which is what is happening at a cruise, is due to a lean condition. Just as your codes suggests. Since it also mentions your EGR, this is a good place to begin since EGR systems can develop restrictions that keep the valve stuck open. When this occurs, there is an internal vacuum leak created by the EGR valve. A vacuum leak is when there is air entering the motor from unwanted paths. When this occurs the fuel system will need to add more fuel to keep the air-fuel ratio in balance.

I would begin by inspection and cleaning our EGR passages. You may need a new EGR valve and other EGR components. But don’t change these components until they have been inspected and found to have problems.

Aside from the EGR system, the best way to inspect for a vacuum leak is with a smoke machine. The next best technique is to use an arosol spray such as brake cleaner. You will want to liberally and selectively spray it in suspected areas.

Another possibility is low fuel pressure.

I suggest having a certified technician, like one from YourMechanic, diagnose your car’s jerking symptom firsthand. They’ll be able to diagnose the trouble code further in order to pinpoint and fix the issue.

Good luck!

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