2004 Tach Mood Swings

[Rod in NC]

Looking at buying a 2004 SVT...overall good shape but needs some TLC. While taking for a test drive, tachometer would act up. While driving normal speed (50 mph), tach would peg out at 8K, no change in actual engine rpm. After a little bit, tach would return to normal operation, then drop to zero. Then back to normal, all while engine maintained constant rpm's. Engine has 136K, sounds solid to me. Never run into this on the 2004 SVT I currently own. Owner says he's had the car for two years, no major issues with the car, just never bothered to fix the tach. I'm wondering what else he hasn't bothered to fix, but I guess I'll find that if I buy the car. Any ideas on the tach? I've see old mechanical speedo's bouncing when the cable was worn...this intermittent tach max/min swing is baffling me. I'm still interested in the car, but hoping someone else has experienced this. Thanks for any assistance. -Rod

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[zetecDon]

Moved to "General Technical Chat".