I have this problem with my 95 formula m6, It ran excellent when i got it last year, but it always ran a little richer than I liked. So I started looking and found the MAF descreened, I rescreened it and my BLM's jumped from 110-112 to around 120-122. I then replaced the sooty plugs with new ac delco platinums and replaced the flogged 02's with new ac delco units. I threw on some new Taylors wires and it ran great, averaged about 26-28 mpg. Then it slowly started this light shake at around 1300-1600 rpms, then after about a month or two the light shake got a little more violent to a point where I cannot even drive it a 70mph in 6th gear. If i drop it into 5th its fine but I'm running 2500, not the best for mileage! It does it all gears if I'm in the 1300-1600 rpm range trying to accel. I started throwing parts at it and now I have an empty wallet and the problem remains, If anyone can help I would be very, very grateful!!!! I can get a datalog tomorrow if that might help!! Thanks!

here is what has been replaced so far in the last 3 months!

2 ac delco o2's
8 ac delco platinum plugs
Taylor wires
Ac delco opti
new water pump
new ac delco IAC and housing plate
new fuel filter
new pcv
new vacuum lines to TB

 

I also unplugged the MAF and drove it and the problem remained, if that matters.

 

Do you still have the EGR? Most times they give a problem just off idle.

 

yeah, Its still on there, anyway to check it on the car?

 

Check to make sure the EGR is tight. It's gasket could also be leaking.

While the engine is idling, squeeze the diaphragm by hand to see if the pintle moves and if so, the idle will get very rough. Do this while the engine hasn't become too warm yet.

If that is moving ok, pull the vacuum line off and plug it and then take it for a ride.

 

I'm pretty sure my car has the same problem. It will do it in any gear if the RPMs are low enough, (below 2000). It does it especially when my car CAGS shifts from 1st to 4th. Is it bad for the car? Also, do you get a noise when this happens? To me it sounds like the transmission is bucking around where it is, also alot of rattling from that same area.

 

Just a point. but my carbed car starts that little shake arrond the 1800-2000 mark for like 300 rpm's worth, and then it is fine. below that it is fine.. and it started all of the sudden one day... No idea what it is.. but it is either the fuel delivery (to rich/lean) or a timing problem at that point.. I am leaning with a fuel condition i think. or a vacuum hose that goes odd at that rpm.. i dunno

 

my shifter starts shaking violently!!

 

Check your transmission mount then.. it should not shake that much.. For hte shifter to shake the trans has to shake.. or something in the trans has to break... I would check to make sure the mounts are good.

 

Hmmm, well my shifter shakes a hell of a lot. I thought that was normal?

 

Well, violently is a little overexagerating, But it does shake pretty good. I have all new energy poly mounts, motor and trans. I am gonna hook it up to datamaster tomorrow and get it to the point where it shudders and see what the fuel trims, timing advance, tps, and map look like.

 

Please share those results of what you find out... carb or fuel injection similar problems have similar fixes... And if you figure out what is causing yours, then perhaps it can send me in the right direction to getting mine done.

 

I got a datalog even if anyone wants to take a look. I am about a week late though, got busy.