oil pressure gauge jumping

[yoozef]

So i bought this 240sx and the guy said the oil pressure sensor was bad. He said he will change it out before i buy it. So i go there n it looks like he fixed it. I pay and drive it back. After like 2 hours of driving the oil gauge started jumping and was going higher and higher and then just all the way past 100psi (max gauge reading). Ever since when i first start it it looks normal, but then once it starts to warm up, the needle starts jumping ( idle the whole time, no driving). And it keeps jumping higher and higher, and when i dirve it it goes past 100. Is that something serious, because the car sounds and drives normal. Thanks for any input

[240dx]

a hem* you my friend have a bad ground