My brother's 1990 RS with a 3.1 and auto tranny is having some problems. The speedometer quit working. Where is the speedometer "sensor or module"? Also, the engine stalls (misses) when taking-off or if it's idling and you just barely press the gas. We have replaced the fuel filter, distributor cap and rotor button. Could it be the catalytic converter?

 

Well, the idling problem could be a few problems.

1) Vacuum leaks.... noted to make your car run bad.
2) Misc. Sensors, you will have to pull codes from the ECM for this, there is a tech article on the main page
3) If the exhaust is not tight, leaking it can cause some missin
4) Timing is off.

As for the speedometer, test the wire running from the speeometer first, there might be a break in one of them, if not go to a junk yard and pick up a new speed module for $5-10.

 

I have tried to pull the codes but can't. I ran a jumper from the top two right "slots" as per the tech article but never could get the codes. I did the same on my 1986 Camaro and it worked. Could there be a problem with the ECM?

 

I think your dam close with the ECM
Horst

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Check the bulkhead connection. when mine rotted away i suffered from rough idle (had to keep giving it gas a a stop) and when I put the key into the "on" position to pull the codes the check engine light didn't come on!!