View Full Version : Small "knock" at idle...

04-21-2006, 08:31 PM
2003 Cobra w/ 14k miles.

I have a small "knock" at idle. Called the dealer and I am dropping it off next week.

Any ideas what it could be? Doesnt knock at start-up, just at idle. Pretty annoying...


Big T
04-21-2006, 11:09 PM
what mods do you have? Did it just start recently after a certain mod was installed?

04-22-2006, 11:05 AM
Nope, havent done anything...

I drive the car hard but who doesnt? :)

Oh well, an annoyance because I want to drive it but it will go to the dealer.


Big T
04-22-2006, 08:14 PM
luckily you haven't done any mods yet. I'm sure it's just something minor. Good luck!

04-23-2006, 08:25 PM
make sure you let us know what the problem is :baby:

04-24-2006, 12:47 AM
Head tick maybe?

04-24-2006, 06:59 AM
Im thinking piston slap, but would need to hear it

04-24-2006, 08:03 PM
Havent brought it to the dealer yet...but my guess is piston slap as well..


05-13-2006, 08:51 AM
could be the valve train assembly, see thread: re-noisy lifter?-follow up

06-02-2006, 10:28 PM
SpikeMT, I don't know your experience, so pardon me if I insult your intelligence with my question.

Do you think the noise you're hearing is the injectors? They can be fairly noisy, but only really heard at idle. They have that "mechanically rythmic" tapping sound to them sometimes.

Just a thought. I hope it turns out to be okay. Keep us posted.

06-03-2006, 09:59 PM
It isnt injectors :)

I sold the car to another dealer...made me an offer I couldnt refuse. I paid 24k and he offered me 26k. I, myself am a car dealer so it is in my blood to make money when it is offered :)

Unfortunately, I am no longer a Cobra owner but I am sure that wont last long...I really, really miss the car!


06-04-2006, 01:15 PM
Sorry to hear you sold it, but guess it is someone elses problem now. A wild guess would point towards the valve lash adjuster. Since they are hydrollic and if one collapses and fails to hold oil pressure the rocker arm will begin to slap around against the cam when the valve spring pushes up on it. It may have been cured with a good motor flush then again probably not. I had a similar issue but only briefly which was fixed with adding solvents to the motor oil and ran the motor for 15 minutes at idle. The filter may have been a drastic removal since I basically shreded it into many pieces just to get it off the car. Have not heard the tap ever since. There is no garranty that solvents in the motor oil will cure a sticking valve lash adjuster but it could not hurt to try it if the tick happens suddenly. There is one reason why I avoid oils with anti-wear compounds since they can lead to issues with some hydrollic parts like timming chain tensioners, valve lash adjusters, and may cause a build up in the oil jets or bearing journals. I had a similar issue with my 01 which shortly happened after using Mobil 1 (which had been reformulated with anti-wear additives). At the time I may not have attributed that to be the cause but it may have contributed to it. Since then I have only used Amsoil or Royal Purple. When I had the similar issue happen with my 04 I used a different brand of oil (lucas synthetic along with the incorrect oil additive, I thought it was the pure synthetic oil stabilizer but got the other stuff which may have cause the tapping noise). The issue only took 500 miles of driving to occur which indicated to me to get it out of the motor ASAP. I do not think it was the oil that caused the issue but more or less the oil additive that did it.