I just bought a 1993 Audi 90 CS Quattro 5-speed. I love it and it has been running great since i bought it in June 2008.
There are a few electrical issues-not major ones but they're still a nuisance.

1. The cruise control works completely at random... IF it decides to turn on, it will usually shut off after 10 or 15 minutes. I do a lot of highway driving (about 20,000mi/year) and cruise is nice to have all the time.
2. At the beginning of November, the driver heated seat stopped working. The passenger seat still works, and I switched the switches for each one so I know that both switches are working fine. I can't even find a wiring diagram to start testing wires for bad connections. Does anyone know even the correct color of the wires I should test?
3. The check engine light will come on when idling but will flicker on and off at random...I'm not sure if this is worth looking into or not. When revving the engine or during normal driving, it does not come on.
4. The gas gauge works when the tank is about half full or more, but once it drops below a half tank, the needle rests on empty.
5. The keyless entry does not work at all. I've tested the remote and it works fine, so it has to be a problem with the sensor in the car. I don't even know where it is located.

A big help would be a wiring diagram for the car if anyone out there knows where to find a good one. I'd be willing to buy one if necessary...even a factory repair manual if that's what it takes.

I really appreciate any help or suggestions that anyone has for any of these problems. I live in the Pittsbugh area and am around Youngstown, OH a lot if anyone knows a good shop that would be willing to check this stuff out. Are these common of Audi 90s? I hate to complain about stupid stuff like a heated seat, but a well built German machine should be fully functional all the time. That's why I sold my Dodge to buy this thing in the first place!

Thanks again for any help! -mjbutera

 

I have a 1993 90 CS, non quattro, and I have had the same problems with my cruise control. There was a thread on here about a way to fix it. If you search the threads for cruise control issues I am sure you'll find it. The heated seats problem...have you tried the relays in the fuse area? Look in the manual for which one is the front drivers seat. The keyless entry is a bit temperamental. The infrared sensor is locate on the door pillar between the front and rear doors. It's real old school technology. If the key/transmitter is working then it may be the sensors. Do all the locks move up and down when you lock/unlock with the key? I know it uses air to raise and lower the locks, so if they aren't moving, there is an air pump likely on the fritz.

 

Found this link to a cruise control switch for the 90. It is easily replaced and relatively cheap.

http://www.autohausaz.com/search/pro...ntrol%20Switch

 

Also this...it's for a 93 100 but it is the same cruise system.

https://www.audiforums.com/forum/sho...cruise+control

 

Awesome...thanks for your info.

I tested the wires in the passenger seat heater in the seat and the ones going to the switch and then compared them to the readings I found in the driver's seat wires. The problem is in the seat element so I'll have to find where to buy one then figure out how to install it without destroying my seat.

When I use my key, it operates all the locks plus the trunk fine...I'll see if I can find a way to test the sensor on the pillar.

I'll have to take a day to work on the cruise control once I wrap up my semester at college...it's been a busy one! I'll keep updates posted the best I can.

 

Summer is here! I'm home from college & I'm going to attempt to fix the cruise control on my 90 CS...I'll keep updates posted.

 

Okay, I know it's been a while, but I finally had a free day today to take some things apart and get my hands dirty. I took both of the vaccum switches off of the brake and clutch pedals and cleaned all the contacts inside really well with rubbing alcohol. After banging my head a few times on the brake pedal and shouting profanity to myself, I got everything put back together. Took the car for a spin on the highway and the cruise seems to be working just fine.
Before I cleaned the switches, the cruise would work sometimes and other times would not, so I hope the problem is fixed. If not, I'll keep the Forum posted.

Many thanks to everyone who sent me the links for stuff. The control unit wiring test was particularly helpful as I was able to narrow the problem down to the vaccum switches.

 

Next project is the keyless entry sensors... and hopefully the drivers side heated seat element if I'm able to locate one to install.