Idle woes

[yamz89]

I have the same problem, but milder... It drives fine, it’s just the low rev control, coming and coming off the idle circuit...

Touch the power pedal and the revs build then click back to idle even though I haven’t moved my foot? Also when you rev up then back off, the revs come down it nearly stalls for a brief second (400 less rpm) then picks up onto the idle circuit and sits at where it should strong (850odd rpm). I’ve cleaned ISV, breather, Rocker cover vents, renewed breather bung, and renewed all vac lines, cleaned the entire throttle body and inlet manifold until gleaming. Also new leads, plugs, dizzy cap and rotor arm.

Only idea I have left is to check the accelerator cable for tightness like the bloke above mentioned.

Add if all else fails, new ISV? But how much are they for a genuine one?

If you work this out please let me know.

Marc

[maxp]

ISV's are about £250 (+/-50) from the dealer, so are a last resort tbh. My pattern part one, which was fitted for all of about 2 minutes, was £40.

Will be taking the throttle body off in a week or two (whenver i can get the gasket from vw) and changing the vac pipes (the one on the back and the one on the right hand side as you face the engine are the more important ones as both of their entry points are on the other side of the butterfly valves) and also checking both valves seal when in the closed position.

I dont *think* its a too-tight throttle cable, as the position of the first idle switch (which also acts as a throttle stop) is factory set (and bolted). Meaning if set too tight the idle switch would never be triggered in the throttle closed position.

[yamz89]

£250 quid?! Still after all these years... Gutted.

I'd only buy geniune anyway but for that money, i'll put up with the woe's.

As i said before, i've changed all vac's, didn't make a difference tbh. Anybody changed the breather valve?

[mattkh]

Add if all else fails, new ISV? Marc

Hi
Have you cleaned the wires going to the ECU ?

[yamz89]

the ISV connetion? no

the actual ECU? no?

[rubjonny]

these problems sound like idle switch and/or incorrect throttle cable adjustment.

check the throttle shuts firmly against the stop when released, if it doesn't cable is either too tight, or the idle switch has been adjusted too far in.  Make sure you hear the idle switch click when the throttle is shut, make sure it still clicks regardless of if you release the throttle quick or slowly release.  next check wiring behind the throttle body hasn't snapped, a common issue on these.

If the above checks out you can test the system electrically if you hold the throttle open to about 1500rpm, then press the full throttle switch on the top. the revs should drop, then rise again once released.  This proves wiring and ecu is ok.

[maxp]

I assume a decent check for seeing if the throttle plate isnt fully closed would be to unplug the isv, fully unscrew the idle screw (currently fully screwed in) and take it from there.

I also thought about removing the big rubber air hose and covering the throttle body with cling film or something a bit stronger to test if its the isv / related systems, going crazy, although the fuel pressure regulator needs a vacuum so im not actually sure what would happen here.

[rubjonny]

shouldnt need to do that, there is a throttle stop on the front of the TB, just make sure the throttle hits it firmly. the stop has adjustment but it should not be touched, unless some biff has been fiddling with it. handly the stop is usually marked with yellow paint from the factory so you can see if its been moved.  Haynes has the procedure for resetting the throttle stop, it has worked for me in the past.

removing the hose wont help you as the ecu wont be recieving a signal from the AFM and the car wont start

[maxp]

Had a wee tweak on the car today despiting the freezing weather.

With the idle screw fully unscrewed, and the isv disconnected, the car sits at around 700rpm (engine note sounds borderline uncomfortably low).

Does anyone know if this is high, low, or should even be possible?
If that rev reading is higher than it should be then it points to a misplaced throttle stop (like rj said)


Checked the throttle cable and there is a bit of slack at idle so i dont think this is it?