I recently bought a 1991 Civic 3 door hatchback. It has 107,000 miles. Everything seems to work fine and it runs great except for one issue. When stopped, it seems to cycle while idling. I don't have a tach, but I'm guessing it goes up to around 1,100 RPMS, then drops to around 700, then cycles through again. It's about a three second cycle. It doesn't always do this, but about 50% of the time it will. Someone suggested it might be the idle air control valve. I can't find this part listed in the index of the Haynes repair manual I have for the Civic. The troubleshooting guide in the manual suggests the following for "Engine lopes while idling or idles erratically":

- vacuum leakage (Are there specific hoses I should be checking?)
- leaking EGR valve (The manual says the EGR system requires special tools and equipment.)
- fuel pump not delivering sufficient fuel
- leaking head gasket (How do you check for that?)
- timing belt and/or pulleys worn (I was planning on replacing the timing belt and water pump sometime in the next month or so.)
- camshaft lobes worn

What do you think I should try first? What is the most common cause for this problem?

Thanks in advance for any help you can give.

Jay

 

Try pulling vacuum lines on the intake manifold(one at a time) and placing your finger over the opening (on the manifold).

If the surging stops when you pull a specific line you have found the area where the leak may be coming from. Could be the line could be what the line is attached to.

 

IAC or yeah vacum lines would be my guess