the shimmies and the shakes
 

when i drive down the road every once in while( more often than not) i will cruise at around 65 in fifth gear my car will just start to shake like crazy like its not getting power or something. now if i give it gas it will cure the problem until let of the gas or if i push the clutch in it will go away. i have a mazda reman with about 3000 miles, pettit ecu, apexi dual air intake, mp, dp, cb. i also have very low vaccuum its at around 11 or so could this be a cause or is it maybe the clutch or dare i say the transmission

Grounds, help alot. I get the same problem and my A/F guage shows lean, probabl from the loop cycle of the O2 sensor. Anything dealing with grounds, and even tighting up your exhaust will probably help. Check it out. Let me know.

if you tape on the brakes rapidly , its like the same kind of jerking motion

my mazda 626 has the same problem, it shakes really bad when cruzing like u said. hope it something simple.

Add another too the list.......highway speeds every so often i get a shake in the back. Feels like a wheel is loose or something. Thought it might be the pillowball bushings but was told that is more of a clunk.
Any ideas??

maybe need to have your wheels balanced by a *good* shop. or a slightly bent wheel that needs a balance to re-balance.

sounds like the engine's bogging. like iits not producing enough power at that given rpm and load to smoothly keep the car accelerating. This can be due to vacuum leaks, lean condition or tuning of that ecu. Since you have a good amount of mods, find your vac leak(s) and take it to your favorite FD tuner if the problem persists.

Does this happen in any gear or just 5th? If it happens in any gear, it is somthing in the wheels/bearings, if it is in 5th, then it sounds like you are bogging the engine. Does it feel like you need to downshift? What RPM does it happen at?

Does it happen above 3200? If not then its your grounds/o2 sensor/ and electrical I have the same problem. Check exhaust for leaks, check grounds for corosion etc.

Don't panic.... I hope its not poor ecu tuning.... Engine leaning.....

it usually happens around 2500 to 3000 rpm in any gear that i am cruising the speed limit in. i do have a bent rear rim but its not bad i also have a vaccuum leak. my ecu is set up to run rich, which it does. and its not just the back of the car that shakes its the whole car.