QuestionI have an 02 Protege5 2.0L that my wife just had to have... it's idling really rough with low rpms, they don't really jump around they just idle low. Just recently, when it starts, the rpm's are at about 1.5 or 2 and then drop down to .5 or lower. It seems to do this really bad when we take it on the freeway or a long drive. The check engine light came on and the code was for a mass air flow sensor which I replaced (along with spark plugs and cleaned out the aftermarket intake) two days ago and it is still acting up. Does it take a while for the sensor to program properly? My only other thought would be that it is the idle air control... what do you think?
I don't know if this counld relate to it but the boots that connect the aftermarket intake to the throttle body had cracked and weren't sealing off at all... i don't know how long it was like that because my wife never looks at her engine but i did replace them about two weeks ago. Please help, I'm a college kid that doesn't want to throw his money away replacing random car parts. Thanks for your time!
AnswerYes, having a vacuum leak from a loose intake fitting would cause this, but the problem should have been resolved when you replaced the boots. It may be that you have a vacuum leak somewhere else. You can find vacuum leaks a number of ways. One way is to use a short length of hose (about 2 feet long) to listen for a leak. Simply hold one end of the hose near suspected leaks, and stick the other end in your ear. Another way is to use carburetor cleaner with the engine running. Note: Carburetor cleaner is flammable and precautions should be taken. You should also have a fire extinguisher near by when performing this test. With the engine idling, spray a small amount of carburetor cleaner near an area that is suspected to be leaking. If the engine rpm's increase, then you have found a leak. You can also use a set of pliers or vice grips to pinch off vacuum lines. If the rpm increases when you pinch a line, then there is a leak somewhere on that line.
If you can not find a vacuum leak, it is also possible that the idle air control (iac) valve needs attention. However, it may not need replacement. Much of the time an iac valve only needs to be cleaned. If you remove the iac and find that it has any kind of deposits built up on it, then clean it with carburetor cleaner or throttle body cleaner. You may also need to adjust the iac. Refer to a Haynes Manual for instructions on how to do this.
You've done a good job of identifying the most likely culprits. I'm sure you'll be able to figure this one out with a little more time.
Also, the end of the semester is almost here, so good luck on finals :)
