Car shakes when accelerating

o1generallee41 · Post by **o1generallee41** » 30 Jan 2012, 17:15

First and foremost I would like to say that I have heard numerous good things about this forum by multiple Volvo owners. I have decided to start here to find my answers.
I have a Volvos S40 2.4i. It’s a 2004 ½ which was the first model year of the 2.4i. However, I have came into a problem as of recently. Whenever I push down on the accelerator, the car shakes. It is especially noticeable at highway speeds where the shaking is actually quite intense. At city speeds (under 40) you can only really notice the shake on smooth roads. As soon as you take your foot off the gas the shaking stops completely.
As far as any indications, the check engine light is on. However, the light has been on from time to time for varying reasons and it doesn’t tend to follow any distinct pattern. In the past the check engine light seems to be tied to a squeaking sound whenever I start a cold engine. The squeak/chirp is only for the first half a send when the car is on (which still persists). However, the check engine indicator has been on since I discovered the engine shake. In the next day or two I will be going to Autozone to get a check engine diagnostic and will update this post with the errors I receive.
As of right now I am leaning towards a fuel related issue. The spark plugs haven’t been change in awhile so it could be a simple fix like that. Any help would be greatly appreciated though. I thank everyone for their time and help in solving my problem.

paddy1965 · Post by **paddy1965** » 31 Jan 2012, 11:25

I had a similar problem with my S40 last month. engine light on and car shaking. I discovered that my tyres were worn out. I changed tyres, did balancing andalignment The result was that the car stopped to shake. The deduction i made was car was loosing traction with finished tyres, with better traction fuel efficiency improved and the engine light therefore dissapeared.

Interestingly in the past engine light went off when car was loaded at the back but when driving alone engine light came on.

o1generallee41 · Post by **o1generallee41** » 31 Jan 2012, 13:42

Thank you for the quick reply. However, i do not believe it is an issue with the tires. The tires on the vehicle now are only on their second season so there is still plenty of tread left. I can see how it would probably be a tire issue if the shaking was constant. In my case the shaking is only when the accelerator is pressed. The shaking stops immediately when you let up on the gas.