Rpm problem

[wolky]

Hi guys, I have a 2002 ford focus zx3 hatchback. The problem is when I started the engine the RPM goes up and then comes down until 500rpm and then goes up to 1000 and comes down again, and keep doing it for about 5 minutes. just up and down up and down. If I keep pushing the accelerator for a while then it comes to normal and doesn't doing it until I stop the car and start again. And it does it even if the engine is warm. I went to 4 mechanics and none of them knows why is it doing it! If anybody knows whats the reason it keep doin it, PLEASE LET ME KNOW! wolky@live.ca

[hEaT]

Sounds like an idle air control problem?

[Lancer211]

Air leak somewhere downstream of the MAFS.

[Liquid_02_ZX3]

Have a shop perform a smoke test to reveal any vacuum leaks.

[beatboxer13]

I had the same problem:

- check your PCV hose
- check MAF sensor
- change air filter

[beatboxer13]

O YEA..

I disabled my EGR via golf tee and my engine always started properly.

[Jason86]

Vacuum leak. Get some carb cleaner, and spray anywhere there is a Vacuum hose. Especially the Crank case ventilation hose. Always had problems with that damn thing. Then listen to the motor. If theres a spike in the Engines RPM after you spray a certain hose, thats where your leak is comin from...

[racer1735]

Where are the main vacuum hoses (primary culprits)? I see a couple smaller hoses in back of the valve cover, above the fuel railings, but am guessing there are more somewhere else that I'm not noticing?

[beatboxer13]

I would also like to know which hoses are vacuum hoses

[sofreshsoclean]

Check the TPS sensor. with a volt meter and see if the voltage is bouncing around. A live data ob2 reader is a real easy way to check the tps voltage. ive also heard you can remove the TPS and start your car and if it idles fine that was your problem (o'corse don't try to drive without it or rev it)

[Pyschovet]

If you haven't found your problem, look below and aft of the throttle body where you will see a hose with a metal band around it. It is approximatly 6 inches directly in the back and below the throttle body itself, it is about .75 inches wide at the start, makes a 90 degree turn and transitions into about .5 inches. This hose is very soft by now with your car, check to see if it collapses when the engine is running. This damn hose caused me so many heart aches I can't begin to explain. If it is colapsing your idle will cycle. The other thing that could cause your idle to cycle is you air intake control motor. Check to see if it is functioning by turning your air conditioning on for about thirty seconds, the idle should increase, then turn the AC off. The idle should drop accordingly.

If you find that is not operational, you could remove it and preform operation check with a standard 9 volt battery. Attach wires to battery and terminal at the motor watch that the actuator move one direction while the actuator extends or retracts, then swap the wires and the opposite will occur. If it is running smooth with no binding it should be good. Before reinstalling, clean carefully with carb cleaner keeping it out of the electric motor. Clean the actuator very well, then push the spring cover down and with a q-tip put some carb cleaner on the surface of the actuator and clean it very well. I stress, spray carb cleaner sparingly and carefully to not flood the motor.

Inspect butterflies to make sure they are clean, if they need to be cleaned remove the entire throttle body and clean it while off of the engine. You should replace all gaskets prior to reinstalling so go out and get some if you plan to take it apart. Removing the throttle body is not for the weak at heart, please check out a Chilton's Manual from the library to use exact steps for removal and installation.

Instead of using carb cleaner to look for leaks, I would recommend engine start spray while spraying carefully on vacuum hoses. Carb cleaner can break down the components of a vacuum hose over time. Hope this helps....

[Pyschovet]

Originally Posted by sofreshsoclean

Check the TPS sensor. with a volt meter and see if the voltage is bouncing around. A live data ob2 reader is a real easy way to check the tps voltage. ive also heard you can remove the TPS and start your car and if it idles fine that was your problem (o'corse don't try to drive without it or rev it)

Just a thought, usually you will get an engine fault light with the TPS, go to a local parts dealer, i.e., AutoZone, Napa, etc and ask them to check faults from your computer.

[G-forces]

Originally Posted by racer1735

Where are the main vacuum hoses (primary culprits)? I see a couple smaller hoses in back of the valve cover, above the fuel railings, but am guessing there are more somewhere else that I'm not noticing?

Look along the back of the IM. Everything plugged in there is a vacuum hose. One big one for the brakes at the bottom, one big one for the PCV in the middle, and three small ones near the TB. If you ever get air leak symptoms, check the PCV hose first, it's prone to failure, unless you have the new armored one.

[sofreshsoclean]

an UN-LIT propane torch works well for finding vacuum leaks. Just wave it around the engine bay with gas flowing out. and when the RPM picks up... you found it.