Idling Too Fast

[shonkers 6]

hi guys any idea why my car is idling too fast ive tried adjusting the idling screw by unscrewing all way out and makes no difference and theres plenty of slack on the cable

[m@ttc 30]

has this just started to happen has any body messed with it like the dizzy? could be the ignition advance is a little out, or the sad device is stuck open?

[Leon 24]

Has the throttle stop been adjusted? This was the problem on my first GTI.

[Miles 331 1 Cars]

Throttle cable catching on something, Make sure the Air screw is adjusted correctly, the Idle screw you should never have to touch from the factory

[bensonmi 4 2 Cars]

air leek on the inlet side?

[pug_ham 242 3 Cars]

ive tried adjusting the idling screw by unscrewing all way out and makes no difference

It won't, unscrewing it will raise the idle speed, screw it in to drop the idle speed.

 

Squeeze the SAD hose where it connects to the afm> throttle body hose & see if it drops when warm.

 

g

[shonkers 6]

hi guys thanks for replies first of all the throttle cable isnt catching and there is plenty of free play,maybe its the throttle stop screw ive been adjusting cos screwing it in clockwise speeds up the engine speed i havent touched the air screw i dont think ,the screw ive been adjusting you have to hold screwdriver in vertical position and its got a small spring clip/split pin going through it

[shonkers 6]

has this just started to happen has any body messed with it like the dizzy? could be the ignition advance is a little out, or the sad device is stuck open?

hi matt its been like it for years but the car has been stood on and off for a few years , i havent messed with dizzy,i should check the ignition timing,maybe the sad device is stuck, whereabouts is it

[shonkers 6]

Throttle cable catching on something, Make sure the Air screw is adjusted correctly, the Idle screw you should never have to touch from the factory

hi miles where abouts is the air screw

[shonkers 6]

air leek on the inlet side?

ill check that aswell

[sensualt101 31 1 Cars]

ill check that aswell

tell us does it always idle too fast now as opposed to before? if not it could definitely be to do with temperature and a sticking sad. my 1.6 often when cold idles at 1500 rpm but generally settles to between 900 and 1000 rpm when warm. what rpm is yours idling at shonkers?

[pug_ham 242 3 Cars]

the screw ive been adjusting you have to hold screwdriver in vertical position and its got a small spring clip/split pin going through it

This isn't the idle speed screw imo but the throttle stop screw which would increase the idle speed when you screw it in, pushing the throttle butterfly away from closed.

 

The air screw is usually recessed into the body but can be a hex head brass screw next to the breather hose.

 

This topic has a guide taken from the Haynes manual for setting the idle speed & a picture showing the idle adjustment / air screw.

 

g

[shonkers 6]

tell us does it always idle too fast now as opposed to before? if not it could definitely be to do with temperature and a sticking sad. my 1.6 often when cold idles at 1500 rpm but generally settles to between 900 and 1000 rpm when warm. what rpm is yours idling at shonkers?

it wasnt doing it before,and it could be to do with temp cos the radiator is not getting hot so im gonna change the thermostat,mine was idling at 2000 when cold and comes down to 1500 when warm,where is the sad?

[shonkers 6]

This isn't the idle speed screw imo but the throttle stop screw which would increase the idle speed when you screw it in, pushing the throttle butterfly away from closed.

 

The air screw is usually recessed into the body but can be a hex head brass screw next to the breather hose.

 

This topic has a guyide taken from the Haynes manual for setting the idle speed & a picture showing the idle adjustment / air screw.

 

g

thanks for the info thats very helpful ill see if i can get idle down now,i noticed welsh pug said if you tamper with throttle stop screw which i have been doing it will create a whole cycle of doom with the tps.also sensault101 said my problem could be temp related which makes sense cos the rad is not getting hot so im gonna check out the thermostat

[mhyphenl 10 1 Cars]

A totally related hijack, I've just put my engine back together and have the same problem. Checked extensively for air leaks, checked the SAD works and closes after a couple of mins. TPS clicks on close and revs go higher if unplugged so that works! I've notced that the revs climb from 1300 ish to 1500 when warm which is strange. Another strange thing is that the charge light is on even though the alternator is working but it went off after a couple of mins and the revs went up to 2000?? Engine MIL light is on so will have to check the codes, if i pop the accelerator the revs drop down for a few seconds then steadily rise again, the MIL light goes off as well for a few secs. I just can't think of what I might have missed. My Oil filler cap is very loose but I was under the impression that oil circulation hoses were not as critical for leaks??

[welshpug 1,627]

engine breathers are critical for air leaks given it is a sealed system with afm.

[mhyphenl 10 1 Cars]

engine breathers are critical for air leaks given it is a sealed system with afm.

 

Ah, right! So the fact that my filler cap is literally liftable with my little finger probably isn't good, I'll try plugging the filler neck and clamping the breather hoses and see what happens! Are gradual inceases in revs with warmth normally leaks??

[shonkers 6]

mine does exactly the same thing blip the throttle and the revs come down for a second

[mhyphenl 10 1 Cars]

mine does exactly the same thing blip the throttle and the revs come down for a second

 

I'd go for an air leak then! Got to test my theory tonight so will let you know!

[mhyphenl 10 1 Cars]

I'm certain its not an air leak as i have rebuilt from the inlet manifold up taking extra care to check everything and its still idleing at 1500 ish. Water temp sensor replaced and tps tested. idle adjustment screw all the way in and still no joy.

Im sure i got the timing right when i built the block but if i was a tooth too advanced would this have an effect??

Any other ideas would be very welcome!

[gsidave 3]

When you say idle adjustment screw do you mean the brass air idle one or the base idle speed. Have you clean out the throttle body recently ?

[mhyphenl 10 1 Cars]

When you say idle adjustment screw do you mean the brass air idle one or the base idle speed. Have you clean out the throttle body recently ?

 

Yes, the whole throttle body was cleaned, i mean the brass big idle screw on the top, the stop screw and tps sensor are as they were before! i'm confident its not anything like that, ive tried them all! I wonder if the vapour valve is working? That may be stuck open, its the only air related thing i've not looked at!

 

Anyone got any knowledge at all about what effect being a tooth out on the timing belt would have on a motronic 1.3??

[gsidave 3]

And you say the brass screw is fully wound in and you have cleaned the throttle body. I personally think you need to set the base idle speed up and go from there adjusting the brass screw.

 

As you have cleaned all the muck that was probably sealing the throttle body it needs closing a fraction ie base idle speed.

[mhyphenl 10 1 Cars]

That's just it! I've set the stop screw as far back as it will go and the idle screw as far in and it makes no difference! Either air is getting in and I just can't find it or something else is amiss! Going in to battle with it again this evening so will report back, in the mean time any other ideas welcome!

[pug_ham 242 3 Cars]

With the brass idle screw turned right in, it shouldn't idle at all so you must have an additional air leak somewhere or the throttle butterfly isn't fully closing imo.

 

For the idle rpm to increase, there seems to be something signalling for more fuel as well, just additional air would make it struggle to idle due to a weaker mixture wouldn't it?

 

Is your SAD closing off when its warmed up? Squeeze the SAD hose to the pipe between the afm & tb once its warmed to see if it drops at all.

 

g