darth

Just to back step a bit, was anything changed or worked on prior to the problem appearing? Have you checked your spark plug wires? How old are they? A light misting of water from a spray bottle while in the dark around coil/spark plug wires may illuminate the problem? If that doesn't uncover anything, try removing the spark plugs for inspection. They are the window into your engine and how it is running. They should all be a dry and tan in colour.

RSGulp

You say "No vacuum leaks". How did you check this?

Pull up a deckchair to the back of the car. Open the engine lid. Open a beer. With a screwdriver carefully tighten every jubilee clip on the inlet manifold half a turn - look all around the engine bay - if you see a clip tighten it to take up any slack. Not too tight - just half a turn to stop any leaks (especially if your mechanics replaced tubes/pipes/hoses last year). Your symptoms sound like a classic vacuum/intake air leak. Once you do this it's one thing we can tick off the list.

Mc.Queen 964

I changed my spark plugs 700 Km ago, my mechanic said that my spark plug wires was in good conditions, and I checked the spark connections and all of them whas OK. But I will check it with the spray bottle..! (I will do it this afternoon)



Last weekend I did that, I put off the ISV, I cleaned the idle speed control valve.. And I took a look of this tubes But this afternoon I will tight them more carefully..!





Thanks guys! I will tell you afterwards.!

RSGulp

Importantly, check the jubilee clips where the intake manifold attaches to the top of the heads - 3 pairs of clips each side of engine above the heads/plugs. They're hard to reach and get neglected because of this.

Good luck.

Mc.Queen 964

I changed them 1 year ago, I put this jubilee clips new.. so I will check them!! Because could be that I leave one not to thigh

Brentflyfish

Interesting thread to me as my idle does tend to cycle up and down between 500 and 1000. i also get a slight knocking sound at times in first gear when pulling away from a stop.

Ryan360

Check your cap and rotor. Backfires and erratic idling happened to me once and the cause was an unseated rotor and badly cracked caps. It was very noticeable at high RPM then progressively at idle as the cap deteriorated. The cap/rotor were brand new made in Brazil when this happened. Good luck.