Odd tach & engine issue.

[1LE]

Well, last week the starter failed on my car. Took it into the shop and had them put a new one on. On the drive home from the shop I developed this new problem:

Was rolling along just fine, hit a bump in the road and the car suddenly sounded horrible (think cross between weedwhacker and a Subaru WRX). I also noticed that my tach was indicating half what it should be for that speed. My digital A/F also dropped to zero.

The NEXT bump I hit (a little ways down the road, while I was pondering the above and considering ditching the car (but also considering the fact that it's the middle of the night and it's about -10 degrees out and I'm still moving barely under power)), the tach fell to zero and the car started running right again. A/F also started doing it's normal thing.

Where should I start on diagnosing this issue? Sure sounds like some plug somewhere between an engine speed sensor and the ECU just loosened up and then fell out or something. Does the tach pull the count from the ECU then?

Just to add insult to injury, the right backup light failed when I got home too. Sigh.

 

[luv2rallye]

The tach signal is from the white wire pin 4 on the 8 pin power transistor unit (PTU) connector (and goes to pin 58 of the ECU). Check to see if this connection and wire is solid. If not that, the PTU or coil may be intermittent (especially if it felt like it was only running on 2 cylinders). A bad ECU can also cause this (eg. leaking/failing capacitors inside).