Idle Problem

I have a 1995 Acura Integra LS. The problem is that when it is cold out it will rev up, then drop down, then rev up and so on when at idle. It does it when it is cold but doesn't always do it. If anyone knows what the problem is I would be grateful for your help.

look for vacuum leak, then Idle Air control valve, then a computer/sensor problem. Often times idle problems like this are a timing issue where the advance oscillates up and down. The ignition issue that causes idle fluctuation is usually caused by one of the above problems.

you can unhook the negative battery terminal and then turn the switch on for a few minutes to clear the computer's memory and try it again. You can test for vacuum leaks by spraying starting fluid on gasket mating seams while the engine is running. A change in idle indicates that there is a leak where you just sprayed.

I unhooked the battery and turned the switch on then reconnected the battery and it still did it. So I went over the lines and noticed a small hole in one. Not sure if it is the cause. Here is a picture of the line the hole is on. Not to good a picture but it shows what line the hole is in. http://www.auctiongripes.com/ims/pic.php?u=2542dgxbS&i=30855

That is the vacuum line for the fuel pressure regulator. If it has a hole, it might be leaking slowly and causing your idle issue. Pull it off, take it to a parts store, and get a replacement 1-foot section of vacuum hose. Usually japanese cars use a silicone-type hose that I doubt you'll find at the store, but you can replace it with regular rubber vacuum hose. It should cost you about 63 cents :)

If that doesn't fix it, at least you've only invested a tiny amount and we can eliminate that as the cause.

Edit: by the way, its not a fuel line, so don't worry. Its just a vacuum line with air in it.

Well after spending .43 cents at the parts it still did it. That would have been to simple.

Well, then I would move on to the other items I listed first. You can try to see if its the IAC by pulling the plug. It would be on the throttle body and you might have to hold the throttle open just a touch with your hand, but if your hand stays steady and the idle still fluctuates then its probably not the IAC. I'm not very familiar with Honda's engine management, but you might find that the engine won't run without the IAC plugged in. If that's the case I don't know the proceedure for testing it. Someone with a shop manual for your car should be able to tell you proper resistance and electrical specs you could use to test it.

Go ahead and try the starting fluid on the gasket seams to try and track down vacuum leaks.

If those fail, I would look to the next distant possibilities. I don't know if your car uses a cold-start injector, but its possible that its not operating properly making a lean condition at cold idle. Its possible that your coolant temp sensor (again, measurable with a multimeter and the right info) is sending the wrong temperature to the computer and not properly enriching cold idle fuel curves. As a long last choice, check the fuel pressure regulator and fuel pump. They rarely exhibit these symptoms, but they can sometimes make funny things happen that don't make sense.

Okay well thanks for all the help.