1991740turbowagon

hi, im new to the forum but have already been on for hours my first day. my question is this - my speedometer seems to work when it wants. sometimes its fine and sometimes it doesnt come on for 20 minutes or goes in and out. as my name states i have a 1991 740 turbo wagon 172k on it and its clean and in great shape. any advice?
also i used the duplicolor bumper coating on my car and it worked great, if anyone wants to see pics email me and ill get you the link
jflmonk@gmail.com
it also seems to idle around 300-400 when stopped, this also is not everytime but it does happen, any advice on that?

sulley007

Welcome to the forum and thanks for being here and a part of the growth. Typically you will see speedo problems because of bad/broken wires at the speed sensor mounted on the differential. You could also have a bad speedo head. You can check the speedo wires by gently pulling on the wires at the sensor. Next you would have to remove the instrument cluster and jack the car up to check for the signal at the speedo head. It is an AC V signal. If you have a signal the problem is in the circuit board or speedo head. Very rarely will you have a bad speed sensor though.

On the idle have you pulled any codes or checked for codes?

1991740turbowagon

no i havent checked any codes, this is only the second volvo i have ever worked on so im fairly clueless. i feel like it just needs to idle 200 rpm higher

sulley007

I'm not sure where you are located, but in the states you can usually go to a PepBoys or Autozone and they will pull the codes for you at no charge. That may give you some idea of what is going on.