04 Mustang shakes violently when running at low RPM's

[WhatAmIDoing 0]

Its a manual 04 Mustang GT with a V8. When the car runs at anything at or below 1000 RPM's it will shake rather violently. Thus making 5th gear and any large amount of fuel economy thrown out the window. Any help would be appreciated and if possible id like to be able to keep it out of the shop so it wont cost me a large amount of money.

Thanks you.

[+John. 1,395]

Is it happening constantly or only when changing/on certain gears?

 

I would check your balancer quick. Mustangs are known for it going, plus if you don't you could end up with a busted crankshaft

[Jim K 13,445]

Check engine light on?  Could be numerous things.  Bad IAC (or other vacuum leak), worn motor mounts, dirty fuel injectors, bad spark plugs/wires/distributor cap...etc.

 

Best thing is for it to be throwing a code (check engine light) that you can take to Advance Auto Parts (or similar) where they'll scan it for free and let you know what error is being thrown.

[WhatAmIDoing 0]

it will happen in any gear but only when its at or under 1000 RPM. Also sparkplugs and coil packs were replaced in the last 1000 miles. Also sorry i forgot to add this before but it has a misfire in cylinder 8 i believe but i dont know if that can change it. Lastly yes check engine light is on

[+John. 1,395]

If it's a violent shake it sounds like it could be the balancer. The balancer basically softens the blow of your cylinders moving up and down.

 

I'd definitely do what @jjkusaf says and get them to run the code though. It'll help narrow it down at least.

[Jim K 13,445]

3 minutes ago, WhatAmIDoing said:

it will happen in any gear but only when its at or under 1000 RPM. Also sparkplugs and coil packs were replaced in the last 1000 miles. Also sorry i forgot to add this before but it has a misfire in cylinder 8 i believe but i dont know if that can change it. Lastly yes check engine light is on

Get it scanned.  That should tell you where the problem is.  As I mentioned (if you're in the US) ... auto part stores will typically scan it for free.

[WhatAmIDoing 0]

Alright thank you both for the help

[+John. 1,395]

11 minutes ago, WhatAmIDoing said:

Alright thank you both for the help

No worries, hope it gets sorted.

[sc302 1,728]

CEL is on...get it looked at/pull codes. 

 

You have a miss in a cyl...this is caused by either no spark/weak spark or fuel. 

 

Could be a plug (well you said you replaced that, so probably not), coil (pretty common), could be a fuel injector (not so common, but they do go bad from time to time). 

 

Really can't tell anything without hooking it up and reading the codes it is producing. 

 

Under 1000 rpms could be anything...clear the errors by replacing the proper parts (again why you need to see what is causing the CEL), we can guess all day long and give you a laundry list from every electronically controlled component, to the transmission, to the rear, to the tires, to the wheels.  How much money do you want to throw at it without knowing the cause of the issue?  I can speculate quite a bit from my end, it isn't happening to my car so anything is fair game, even your wipers and radio.