strange noise, tach malfunction
 

Sorry if this post is a bit long winded. Thanks if you decide to read it.

Driving my 90 gtu the other day, I got on the highway in 2nd gear and put my foot down. The car would not accelerate past 6000 rpm, and I could hear a loud rattling/clicking noise from the drivers side of the engine bay. It freaked me out so I drove the car very gently to its destination. Cruising at about 3500 rpm, the rattling/clicking noise was cutting in and out. Whenever I could hear the noise, the tach needle was wiggling up and down by about 300 rpm.

I've since driven the car and it accelerates normally to redline every time, but the clicking/rattling sound and spastic tachometer are still present. The noise, always with the tach wiggling, cuts in and out while driving at a constant speed. It happens for about 20-40 seconds at a time, and it seems to occur less frequently the longer I drive the car.

I have some ideas about why it wouldn't go past 6000 rpm, but the clicking/rattling and tachometer strangeness has me worried. Next time it happens I'm going to try disengaging the clutch to see if that affects it.

There are some other issues with the car that I'll list below as they might be related to the problems that I described.

- My CEL blinks when I accelerate hard. The error code is 13. I've replaced the hose to the pressure sensor, with the plastic orifice in the new hose. I've also tested the pressure sensor with a multimeter and the readings seemed normal. I'm going to replace the sensor anyway.

- When it's very cold outside, the car will not idle without assistance for the first 30 seconds after startup. After 30 seconds, it idles normally. (~1500 rpm, down to 750 as it warms) The throttle body is set up perfectly.

- The transmission makes excellent whining noises from 3000 - 4000 rpm in every gear. I don't think that this has anything to do with the above, but it's included for completeness.

What could be causing the clicking/rattling and tach wiggle? Any suggestions about that or anything else are welcome.

find the end of the tach line. The thing that connects to the trans may be coming out and causing a rattle. It also could be a clogged cat.

Tach line. Hmm. Have fun finding that.

I think he meant the speedo cable? I hope anyways! But regardless, that has nothing to do with the tach. The tach gets its input from the trailing coil. If it were loose, it may mess with the readout, but would also mess with the running of the car... maybe it is loose?

Brain fart - thinking of speedo Cable.

^^What he said