Hey I have an 88 Honda Prelude 2.0si fuel injected and DOHC. The engine idle revs up and down constantly. I have thoroughly inspected all the vacuum lines for leaks and nothing. Any suggestions as to what else it could be?

 

I had this problem with 89 Honda CRX HF. Dealer checked it is the alt. Because the PCM depends on a clean DC voltage and it is likely that your alt's diodes getting tired. The PCM is confusing with dirty DC current (or AC current). Suggest go to dealer and hook up with their scanner. If they say it is ALT, then you fix it yourself. Good luck