Intermittent tachometer

[josephvman]

I've had an intermittent issue with 3.2 Targa that I've suspected was related to the DME module, but I thought I'd post this before I pulled it out and sent it in. The tach died a few years ago and while I had the engine out to address a lot of stuff we sent it to Palo Alto to be checked. They didn't indicate whether or not they found a problem, but it has worked for the 3+ years since.

I've had an intermittent surging idle issue on cold start that comes and goes in frequency, and will go months without a hiccup. I checked the idl control valve, and it was very clean an clicking on/off as it should. My shop checked for vacuum leaks, and ended up changing the fuel pump this summer, but still have the issue on occasion. This week the tach went intermittent, completely dead for a couple of days, but started working again yesterday. Today it started dropping out when I'd clutch the car, then resume working when I engaged the gear and was under load. Evertime I'd push the cluth at speed it stops working, and resumes when I release the clutch. I made a video you can see below. The car has a SW chip and M&K exhaust system. I've checked all connections and everything looks good. It started wroking the day I planned on pulling the tach, but I pulled it out halfway to see if movement affected it, shook it lightly and moved it around to see if it might be a connection at the tach, but it never stopped working.

Pretty sure it's DME related, so I'll probably pull it and send it in this wekk, but thought I'd just see if anyone else had run across a similar issue.

In the video I'm just pushing the clutch in, tach dies, releasing it, tach comes back.

[zuch]

I'm having a similar problem. Did you ever figure this out?

[Ok here we go]

For what it's worth, I had a dying Tach and Speedo for the last 3 years that showed intermittent spurts of life on occasion. I had the same experiences @josephvman did so I had John Bell repair both, but it still didn't solve the problem. Recently, my 3.2 had a no-start problem where it would crank but wouldn't turn over. I ran through the whole gamut of tests, and I ended up sending my Motronic unit over to Sal Carceller (thanks Sal!!!) for repairs. The cracked and old soldering in the Motronic ended up being the culprit, and after the repairs were made the 3.2 turned over like clockwork. Somehow, magically all of my Tach and Speedo problems never happened again.

[Ian Comerford]

I’ve had this problem once before about twenty years ago and it was a failing voltage regulator

[911obgyn]

The tach on my 3.2 occasionally drops out, i tap it and it comes back, reminds me of the old black and white WW2 plane movies.