Tachometer quits intermitently, now with CEL, and missing

[signless]

Hello everyone, I have a 1990 Legacy L Wagon, 2WD AT with 2.2L. It has recently passed 220k miles and runs great. Six months ago, the ECU failed, and so because of my confused mechanic I have a new (well junkyard) ECU, cam and crank sensors, ignition unit, and timing belt (which was long overdue anyway).

 

So, the last 6k or so I have had a very occasional problem where the tachometer will drop to zero while the engine stays fine. Ten to twenty seconds later, it returns. I have only ever noticed it when driving fast on the freeway. None of the other guages drop, and no lights come on - except yesterday. For the first time, the loss of tachometer was accompanied by a check engine light. So, it's starting to concern me somewhat more.

 

Now, I know the tachometer thing is likely to be a bad connection in the instrument panel. But I was searching here and I found this thread:

 

http://www.ultimatesubaru.org/forum/showthread.php?t=6059&page=1&pp=10

 

For the last 50k miles, I have had a more frequent problem somewhat like this - the engine will idle rough, up to about 1800 RPM, then smooth right out. Every week it will happen a couple times, but I just push through it and a minute later it goes away. Now it makes sense to me that THIS problem could quite likely be caused by the idle air sensor.

 

So, I guess a just want a little direction for my troubleshooting. I'm assuming that the tach problem isn't a problem with the crank / cam sensors because the engine runs fine - even if I floor it while the tach is off, the engine responds perfectly. Could anything else, say the IAS, be causing the tach problem? Are my two problems related? And if I need to dive in to the instrument cluster, is there a good guide for that anywhere?

 

Thanks for your help everyone...

 

JT

[Legacy777]

Pull the codes from the ECU. Instructions are on my site.

 

More then likely you'll find the code is the vehicle speed sensor 2. It's located in the combination meter (dash), so you'd pretty much have to replace the whole gauge cluster if the speed sensor is bad.