ShadowDrake

Not all of your cylinders are firing is my guess. The engine will idle all the way down to only three cylinders (even all on the same side next to each other) but it will idle lower (650-700) and shake badly then... no check engine light came on with about 5 seconds of running like this, which is very strange. While I don't think all of them are doing that, it may be one or two, examine all your plugs if you haven't already. A coil or two may be bad.

kubball2005

I replaced the coil that went bad before and when I took the car in to have the helix coil put in the mechanic checked all my other plugs and said they were secure and working. How can I check the coils to see if they're working properly??

kubball2005

I put the stock tune back on the car thinking that the timing might have gotten screwed up somehow. After putting the tune on the car still idled weird and shook bad when i was sitting at a light. The car will idle where it normally does for a second then drop down to almost 500 rpms, and the car just starts shaking. This is really bugging me and I wanna get my baby running better.... any help would be appreciated.

kubball2005

C'mon guys, any thoughts?

buster

u have a vacuum leak around your intake pipe (PVC valve etc). make sure they are all sealing properly and not cracked. Your car is 7 years old pal, rubber and plastic deteriorates over time. If not, sorry that's all I can think of. Check for a leak by spraying some eather around the intake with the motor running, if the motor speeds up there is your leak.

Miliock

before you said that the original tune made it worse I was going to say it could be the pressure plate? for the clutch. I'm not sure if it's called the pressure plate, but if it's uneven it can cause vibrations at lower rpms.

CJFANNI

Check ur dtc codes in ur tripometer

kubball2005

dtc codes? I used my predator to run any trouble codes and there were none.

98DropGT

Yeah figure this one out i think your having the same problem i am ....
right about 1800 rpm using just enough throttle to hold speed my car has like a hesitation, at idle rpm will drop to 400-500 and it shakes the car just enough that you can feel it ...
but thats only one of my bugs at this point, the car also has a bad hesitation if i run up around 4000 and let off when i get back on the throttle the car sputters/hesitates for a second then takes off.
CEL is on also it started comming on after i installed cai, i had the code pulled before and it had something to do with running lean on bank 1. i was told it was possibly my cai and ecm tuning should fix it ... so right now im waiting on delivery of the sct xcalibrator 2 we will see

1998 GT Drop Top
BBK Fender Mount CAI
Flowmaster 40's
2.5" Springs
18" Falken Hanabi Wheels

dlazrael

My ex-gf had a similiar issue in her 2001 3.8L ( i know its the 4.6L dont hate!). It turned out to be two bad coils, sorry mate, but that's probably what you're looking at.