Thread: Speedometer jumping to over 100 on acceleration

I am having a problem with the running and acceleration . When I try to accelerate from almost any speed, the motor stumbles and surges, the speedometer goes from the current increasing speed reading to displaying over 100 for a second or so, the SC boost gage is constantly showing a couple lines of boost (even at idle). sometimes when coming to a stop at a light or in traffic the motor will go from idle to RPMs dropping to 200-400 and then die, and then hard to restart. ( Not every time)
As background, I just replaced the motor with a used motor a couple weeks ago, got a couple codes after a couple 100 miles ( missfire cyl 1, and egr code) swapped coil from old motor and cleared codes, ran great for aprox 100 miles then codes came back and started running erratic .
The motor I installed still needs the SC coupler replaced, but need to straighten out all of this first. I drive the car daily 125 miles RT to work.
The SC boost gage showing boost all the time just started tonight on the way home, and it does run differently when on, so I don't think it is a malfunction with the lights.
I have cleared the codes a couple time so far, and it will run fine for almost a full commute, then it shows back up.

HELP !!!! Don't know which way to go from here.

Also, I will have a complete top swap for sale when I get all this straightened out, and the rest of the old motor also. What are these going for these days?

Gas milage according to computer is 22-24.
Now on the way home tonight I have a whole new set of problems....
I stopped and read the codes before hitting the interstate , had 3 codes P0121 throttle position sensor error, P0440 Evap control system malfunction, P0449 Evap control system vent/valve solonoid malfunction...
These are different codes than I have gotten before. I cleared the codes and headed for home (55 mile trip) car was running good, no hesitations or stumbles in stop and go traffic. Then about 1/2 way home, it started acting up... I was running along around 50 mph and when I would try to accelerate the tach would go up to around 5000 rpm and drop back down, but the motor was not reving, it was actually bogging like I had ran out of fuel, thought the motor had died , but was still showing 2000rpm, I worked my way to the shoulder, and the it started pulling again. It did this several times the rest of the way home ( also used over 1/3 tank of gas on the trip) I was able to limp it to my exit, and pulled into gas station to refuel and check the motor.

I was pulling on the vacume lines to make sure they were attached, and the one to a point by the boost bypass valve broke off in my hand. reattached good enough to get home (5 miles)... seemed to run a little better.... but of course the check engine light came on about a mile from home... and it seemed to run even better,,, go figure.

Since the problems seem to be going all over the place,,,, what is the chance the computer could be going out? Would I get these kinds of problems? What sends the MPH signal to the HUD?

I am getting more confused every day with this thing.... I NEED HELP !!!!!

Thanks for all the help I can get.

Yeah, it was just the HUD that freaked out. hope one of these guru's has an answer or at least a direction to start in.
Had to turn around this morning and bring the car back to the house and swap out,when I stopped at the stop sign leaving the neighborhood, it started dropping off idle to around 300 RPM's and almost dieing a few times in a couple seconds. Getting really tired of all the problems...