Surging during idle
 

Car: 2001 Boxster S

Problem: When idling the RPMs go up and down from 700 to 900 and back again in about a 3 second cycle. If I turn on the A/C the idle settles down and is steady. Only occurs with the A/C off.

I hooked up a ODBII scanner and get no codes from the engine at all.

My mechanic thinks its a vacuum leak - any suggestions?

Thanks,
Francis Govers
Nashua NH

2001 Boxster S Polar Silver/ Black int.

Clean your throttle body.

Did you recently perform any work that required you to disconnect the battery?

It can take a few driving cycles for the computer to "relearn" its settings.

If you haven't disconnected the battery recently, Jager is likely correct.

I agree with Jager. It cured my surging idle problem.

Classic symptom +1 Jager

Solved my surging idle
Check your air filter and MAF(MAF Cleaner) while you're there
If you take apart all the plenum tubes for cleaning, mark their positions relative to their clamping couplings. Once you put it all back together, it's hard to know if everything is centered

+1 on cleaning your throttle body. :D

The reason KevinH1990 asked if you've had your battery disconnected recently is because when you disconnect your battery your ECU reboots itself. It then has to relearn all fuel trim,afr, ect..