[Purist]

I've been having this problem sporadically for the past few days (2005, no engine mods). The first time happened just as I was about to head out onto the track at NHMS :wallbang:

When idling, the revs repeatedly jump up to over 3k and fall back down. It does this randomly, with a frequency of about once every 2-3 seconds. At the same time there is a "puffing" or "gasping" sound from the engine. Also at the same time, the speedo needle jumps all over the place. If I give it throttle, the surging stops but the speedo needle keeps going crazy. Same thing if I unplug the IAC valve, in which case it just idles a bit high (~1200 RPM).

I replaced the IAC valve a month or so ago, and I can confirm that the trottle is closing all the way and staying there.

Seems to me like I have a systemic electrical problem that is affecting the IAC and speedo, but have no idea where to start to isolate it. Ideas?

Thanks folks,
Tom

 

[charliex]

does the rpm needle jump around too ?

could be electrical, could be a vacuum leak and unrelated cluster problem.

monitor the voltage with a DVM, check for leaks http://www.lotustalk.com/forums/f101/diagnosing-vacuum-leak-67632/ , check battery connections.

 

[Purist]

The tach does not jump around (unless the revs themselves are jumping around).

Where's the best place to check voltage?

I don't think they're unrelated as both always occur simultaneously.

After checking the voltage, I'll check the batt connections and then start thinking about vacuum isues.

Thanks for the advice Charlie,

Tom