97 F355 Tachometer Reading Incorrectly

My F355 was just in the repair shop for a rough and high idle along with the installation of new emergency brake shoes. Repairs that were done were the installation of the crank trigger sensor, a new MAF and a coolant temperature sensor. The second trip/ride out of the garage my tachometer reading started to act up.

First, when I started the car is was revving normally, but the tachometer reading was showing it was at the 20 rpm mark. When I was driving the car the tachometer would not move lower than the 20 rpm mark and not higher that the 30 rpm mark. While this is happening the engine was running and shifting normally. It appears it is just the gauge reading and not the engine performance.

Periodically while on my drive, the tachometer after being stuck between these two spots, would revert back to normal driving readings and work for a short time only to get stuck again.


Now on my third and fourth trips out, the rpm reading just stays between those same marks as described above with it not reverting back to a normal reading.

What do you think is causing this? Loose wire on one of the parts that was added? Please let me know what you think and thanks for your help. Seems like a simple fix?

 

I saw a recent post and a reply from pnicholasen in which he stated to tap the tach because sometimes the needle gets stuck. Great simple advice that worked for resolving my dilemma. I did not think the fix would have been so easy. I appreciated your incite pnicholasen that I stumbled across the other day. I wonder what my cost of repairs would have been if the vehicle would have gone in the shop?