I have a 1985 tuned port injected z-28 with a 305 in it. As i was driving around the other day the check engine light came on as i was sitting at the stop light, and started to idle funny (1500 then drop to 5 for split second then back to 1500 or so for another 10 sec before dropping back down to 5 again) so it would do this alternating back and forth while i was sitting at the light. when i would start to go again at about 30mph the check engine light would shut off and the car would run fine except there is mild spark knocking from 3/4 to full throttle under any sort of load. When i got home and pulled the code, it gave me 24 which in the chiltons manual say it is the VSS. My question is will the vss be intermitant like that? how can i check to see if it is bad? also the wiring diagrams that i have say that it is in the cluster gage, can anyone verify this if i have to take it out? Also i do think that my speedo is off a bit maybe 10 mph or so.
If anyone can give me some answers to this it would definatly ease my mind! thanks
john

 

first off... yes the vss in your car is behind and attached to the gauge cluster.. from what you are saying is happening it is going bad.. mine is doing the same thing.. though mine is attached to the tranny (electric speedo) the symptoms are the same as mine and i have change the vss only to find that i have to now change my drive and driven gear cause someone had the wrong ones in.. my car did this all when i bought it a few weeks ago and i just got the parts i need to do it. but that is what it sounds like.. hope that helps some