Idle And Start problem

[Zijo]

Idle And Start problem

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So for the last three weeks, off and on when I start the car idle it just goes up and down. Right off the bat the engine will rev to about 1200, then drop down below 500 and bounce up and down for a little almost stalling.After 2 to 4 min idle gos from 800 to 1000 up and down. Then if i turn fan on idle go up to 1500 and stay there until i turn fan off..

Please help i need to do SMOG Chek it will not Pass.

Jetta 1990 1.8L gas.Automatic

[Doug Tatham]

Your idle stabilizer needs to be cleaned. When you turn on the A/C it automatically adjusts the idle up which is why it helps. The idle stabilizer is the metal cylinder connected to hoses that sits above the valve cover. Use carb cleaner to clean it. Fill it up with cleaner and use a small screwdriver to move the valve up and down until all the build up is gone.

[Zijo]

I clean idle stabilizer and I Replace with new one and still working Same nothing changed..When i first replace works fine for a day or two then Start working same all over again.

[Doug Tatham]

I'd check for vacuum leaks. Check the PCV valve. Make sure that your oil cap is sealing (it can be a source of vacuum leak). Check to see if something has gummed up the stabilizer again.

[Zijo]

I find Vacum leak and fixed.
Yh You All for Help..I still have one more Problem .