Noticing the tach needle jumping around quite a bit on my 1994 Bonneville SE. Can feel the car hesitating when this is happening but no lurching. The ol 3800 series I has had alot done recently...new crank sensor, IAC valve, EGR valve, PCM, ICM (about 1 year old), I've cleaned the contacts including the buss bar...none were corroded but cleaned anyway. Changed the upper and lower manifold gaskets, new plugs, O2 sensor. I do have a SES light on along with an ABS light on. The autozone nearest me isn't equipped to scan the '94'* (so they tell me). Any thoughts ? The transmission still shifts smoothly so I think I can rule that out. Car is smooth at idle (thanks to the new EGR valve) but tach needle will jump around once I'm underway starting at about 30-40 mph. All vacuum lines are in place and in good condition. Tried the MAP sensor test...appears o.k. Sorry for the novel....just trying to paint an accurate picture......Thanks for any help

Have a look here
https://www.gmforum.com/showthread.php?t=278980

Look under the dash and let us know what kind of OBD port you have.

OBD1


OBDII


If you have the first one, then you can do the paperclip test to get your codes.

Mike,
I looks more like the OBD II port. Did they make an OBD 1.5 port ? for that year (1994)

Trixster,
Thanks to this forum I had already done that previous to the problem and mine wasn't as bad but I cleaned it up anyway and put a coating of di-electric grease on

No, if you have the 16pin OBDII port, you need to find a scanner that can scan 94 and up. Only one Actron scanner that I know of can, and the dealers Tech 2 can also.

Mike,
Thanks....and problem solved had it scanned and turned out to be a TPS sensor will tackle that tomarrow.