eratic idle help

its a digifant 8v,standard apart from a cone filter.
the problem is its started to rev itself then sit at 2000-3000rpm,so far ive checked all the vac hoses and changed the i.s.v,what else should i look at?cheers

 

Reset the idle as per the Haynes manual....making sure you do all the rev to 3000rpm 3 times business!!! Remove & clean the idle screw first & check the o-ring on it is in good condition. If perished replace with a new o-ring (available in halfords o-ring multipacks...about 75p)

Sounds very high for a simple idle problem though. Check the wiring to the throttle body microswitches too & check the air inlet hose for any splits...

Could well be an air leak!!

 

My 16v GTI runs ok for 5 mins with the idle at just over 1000, then after 5 mins if I change gear with the revs over 2000 the idle sticks at 2000, I have to drop into a high gear to take it below 2000 and then the idle settles back down to 1000.

I've onlt had the car one week

 

Dub,

1. Throw away the cone filter. It's not doing your performance any good. It is bypassing the whole cold start mechanism. The only reason to have one is the sound.

2. Throttle position switches. You have two on the back of the throttle body, one registers fully closed throttle, the other wide open. Check both click at the right positions, and that the wiring is intact back to the ECU.

3. Chris is right, idle screw. It is used by the engine to stop it stalling on overrun, while the ECU starts up the control of the ISV. It should be set so that when you take your foot off at 4000 rpm, the engine drops to 800 ish before the ISV kicks in and starts controling to 850rpm. IT DOESN'T ADJUST THE IDLE SPEED. It controls the starting point for the idle control program in the ECU.

Simon.

 

thanks for that tow dub.bass!

 

i tried everything,apart from the throttle switches .same simptoms as fuggy gti though

 

It really sounds like your throttle switches. It might thw switches themsleves, or the wiring to them.

simon.

 

Yep, the closed throttle switch sounds stuffed, or a broken wire to it.

This has the effect of the ECU receiving no throttle closed signal so doesnt know to initiate the overrun cut off/ ISV circuit when you close the throttle...

This gives the effect of the car driving itself along when you back off totally & the revs hunt around 1500-2000rpm