Ok so yesterday my gf was following me home on the highway in her 00 a4 1.8tq I was trying to make sure she didn't get left behind on highway since she never drives on it we'll I was only doing 60-70 mph she said her speedo said 70-80mph that's kinda a lot off not CEL Or anything what do you buys think

 

Do you have stock size rims and tires, or have they been changed to something larger?

 

There stock 16s with 205 55 16s on it we did swap motor and trans In the car but came from identical 2000 with the same 1.8t and EFQ trans

 

Anybody

 

Maybe her's was off? Were you passing a whole bunch of people, or more or less just keeping up with traffic?

 

That's what I said her speedo is off In her a4 I was doing 60-70 keeping up with traffic she had to do 70-80 to keep up with me so when she was doing 60-70 everyone was blowing by so this issue is how to fix her car

 

Do you have a VAG-com to scan the cluster? The logical answer would either be that her cluster is busted, or else the speed sensor needs replacing. No clue if either would throw a CEL, but they might throw codes regardless.

 

No vag but I have a spare cluster I can swap In and try that

 

I think you're going about this the wrong way.

You're chasing a "problem" that may not exist based on a 10-20mph variance in speed from two peoples' memories at different times.

Do you have a GPS? Compare the GPS speed to your car's speed.

I could be wrong, but I would bet your speedometer is working just fine. If it wasn't, I doubt it would read +-10mph. Usually they either work or they don't.

 

If possible, go out on the Interstate or other freeway with mile markers. See if the odometer shows 1 mile from marker to marker. Then drive 60 mph and time it. Should take 60 seconds to go 1 mile. That way you'll have a better idea if it's wrong or not and then go from there with diagnosis or repair.
Can't really rely on GPS. I've seen some of the lower priced ones be off upwards of 5 mph either way.