Roblen91GTA

Ok so i have a slight miss on hot idle its pretty noticeable and driving me nuts the car idles at 600 in drive but once in park it slightly shakes and the tach bounces between 600-650 rpm. the car has fresh plug/wires/msd coil and a digital msd box...box disconnected same thing with idle. Also when i put it in drive or reverse when hot at 600 rpm right when i let off the brake the car moves and it moves pretty fast for me not being on the throttle and only at 600 rpm other than what i listed the car runs perfect and pulls hard, any help greatly appreciated thanks

Roblen91GTA

Anyone have any input?

chevypower91

Did you experience this symptom before updating the ignition with msd or after?

Roblen91GTA

thanks for the response, I might have had it before but maybe i didn't notice it to much but if i disconnect the msd box it still does it and shakes a little bit more. could it be my msd coil that was taking a dump? i don't think its the TPS or IAC

chevypower91

Does it misfire at all under load?

Roblen91GTA

Nope it smooths out and is totally normal and it doesn't stall if you were wondering rpms never drop below 600 but you can deff feel a miss or like a hitch on hot idle

Roblen91GTA

Could it be motor mounts making the car shake a bit? and the tach bouncing 50 or less rpm be normal for these cars? anyone have trouble with motor mounts before?

jdenowh

Its not the motor mounts. I am experiencing the same problem. Ive changed just about everything and cant figure it out. IAC, TPS, plugs, wires, dist, coil, O2 sensor and computer.

Roblen91GTA

Thats strange maybe its a normal thing with these cars when they get older. and you replaced more things than i have and you still have the same problem. Also i need to ask does anyone get a jerk when you shift into drive or reverse and there is no shifting problems while driving just the initial shift, i swaped the trans mount twice so it cant be that

86T/A_Ram_Air

That's one of two things. Engine speed high when you shift it into gear or the springs in the valve body are worn

Roblen91GTA

I would probably guess its transmission/valve body related. but i cant see the trans making it shake and vibrate at a stop...or can it

johndinu

mine does the same....
put new injectors in, will report back

Roblen91GTA

yeah i have new injectors in there not those stock crap ones haha. I did notice since im driving it more its not shaking nearly as much so maybe it just wants to run more and plus the age it wont be perfect but at least im not the only one with the same feel

leo27030

hey I'm having that same problem your having and I've replaced just about everything under the hood all the way back to the tip of the tailpipe. the only thing mine was doing different is the oil pressure would drop just above the red ,and it would stall but start right back up. So i just had the oil pump and everything related changed , thought it was fixed but within about 3 miles it started acting the same minus the stalling . if you guys ever figure it out please let me know .......

jdenowh

I just swapped out the fuel pump and filter and the problem has gone away.

johndinu

ok after the bosch gen III's from southbay and a set of ngk platinum, idle really cleaned up. car runs like a bat out of hell. could't be more satisfied

Roblen91GTA

Wow that would really bother me but that sounds like your problem might be the ecm going bad where the car stalls and fires right back up i would give that a try. As for my problem i just did a simple oil change (mobil 1 synthetic) and a fuel filter and the car it a lot smoother. the previous owner changed the injectors so idk whats in it now but if they crap out ill be sure to get some from southbay i hear a lot of good stuff from them

Linson

shouldnt the "desired idle" in park be around 700 RPMs? maybe if you bumped up the idle just that little bit, that could fix the shakes and the bouncy tach needle.

as far as the hard-charging when off the throttle, i had that symptom after my engine was rebuilt. it was caused by a vacuum leak. i also had very little braking power. if i were to look for a vacuum leak, the first place i'd look is at the TPI runners. better yet, take it to a shop and have 'em hook it up to a smoke machine.

edit: come to think of it, if you fix any vacuum leaks that you might have, that will likely sort out your idle issue.

Roblen91GTA

Well now it sits around 650-700 and the tach isnt going to be spot on but i think the idle is set fine.
I did the carb cleaner trick to check for vacuum leaks and its was all tight but all good things to check out