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rpmdiag, Tech and Instructor
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Experience:  Since 1975
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rough car starts..I accelerate faster like on the highway

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Hi, I have been noticing my car is starting to rough idle and when I get to about 40 my car starts to shake. It only shakes when I accelerate slowly when I accelerate faster like on the highway the car does not shake. What could be the problem?



You may be developing a slight misfire in the engine. Tell me more about what you're driving, year, make, model and engine size. Also tell me if the check engine light comes on.


Thanks for your question and positive feedback,



Customer: replied 7 years ago.
Hi thank you for your help, I just sent the information under the already tried section

graphicOkay, if the system is running lean, it's not the O2 sensors' fault or thr plugs. The first thingn I wouldm test would be the MAF sensor ouput. Here's a scop shot of a good one. This component can cause lean conditions.


Thanks again,





Customer: replied 7 years ago.
So could it be that the system being too lean is causing the rough idle and the shaking when I get to 40mph?

Sure can, we need to find out what is causing this lean condition and this is the best place to start.


Thanks again,



Customer: replied 7 years ago.
Could it be that the MAF sensor is just dirty could it just be cleaned? I know that they are somewhat expensive to buy. What do you recommend, I know that when I go to get my car checked they always just want to replace parts, could I just clean the sensor myself?

Thank you for all your help

Try cleaning it first, and if it helps you're good. Most of the time the problem is a defective MAF though.


Thanks again,



Customer: replied 7 years ago.
One last question, sorry for the trouble, but if it is defective, how much should I expect to pay for the part? I would prefer to get an estimate from someone thats an expert and is not just thinking of making profit.

Again, thank you for your help and time

It first needs to be tested, then the part is about $150.00 the labor is only 20 minutes.


Thanks again for your support and positive feedback,



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