Throttle Body Bypass Idle Confusion!!

[mannings 1]

So bit of a long story but suffice to say I've read every post on here on high idles on my 1.9. It's been a saga and I am very close to the holy ground of a 950rpm idle when warm. But still at 1250rpm fully warm but with throttle bypass brass screw fully in. 

Check lots for leaks with carb cleaner on everything. Timing is bang on as pulls like a dream and only slightly pinks up a hill in third. Both the diaphragm in the dist and one way valve on the brake cylinder are new and holding. No leaks on valves, oil inlet screw is tight plus ptfe. 

 

The odd thing I noticed if I gently rotate the throttle arm slightly more with my hand it bang on hits 950rpm..but the spring and pin natural position holds the revs at 1250rpm. I have cleaned thoroughly the TB and bypass screw to a shine. The throttle switch is bang on. 

 

Looking down the barrel of the TB the butterfly paddle thing has a 0.1mm gap all the way around and wonder if that is right..should it be air tight or at least closer than 0.1mm? 

 

Really appreciate any help and sorry for the veterans on the site responding to another high idle post. I've just run out of road and need some new ideas to check.

[mannings 1]

Sorry the throttle positioning pin is retracted so the TB is fully closing and the pin is not holding the throttle open 

[mannings 1]

Sorry additionally sad is fine and revs drop when cold and pipe pinched then don't when hot. 

[welshpug 1,661]

sounds like the throttle switch is holding the throttle open.

[mannings 1]

I've tried to set the switch so it clicks as you only just open the throttle. Is it worth setting it to allow more throttle travel before the switch clicks?

[DamirGTI 342]

3 hours ago, mannings said:

revs drop when cold and pipe pinched then don't when hot. 

 

If the revs don't drop with the SAD hose pinched while hot - you're missing (switched) 12v supply to the SAD heater element (connector problem , wiring problem etc.)

 

For the SAD to fully close after warm up period , it needs both : heat from the cooling system and 12v supply to the heater element .

 

D

[PhilNW 44]

Have you had a look in Haynes manual there is a specific sequence for setting everything up.

[mannings 1]

Thanks very much. Have done those steps already but let me redo it all and report back. Thanks 

[mannings 1]

So went and checked a bunch of stuff. Throttle switch is correctly positioned and working. Need to take to mates garage with CO meter to do the mixture set up but not worried about that right now. Timing should be bang on but will check once get hands on a light gun. 

 

Interesting/ confusing part came when I went to complete section 26 of the Haynes Manual chapter 3 to complete a "fuel injection system - complete test". 

Task 1 and 2 looks for a switched live min 9v from airflow sensor connector wire 18a to earth. And Task 12 does the same for the sad. Neither returned any volts. Meaning either they aren't getting them or I can't work a multimeter (quite Possible!). If the airflow sensor didn't get a switch live would the engine start and run as well as it does? 

Where else would get a switched live so I can check and remove multimeter idiot factor from the above equation? Or does this indicate maybe one of my issues noting your point above @DamirGTI?

 

Task 10 also looks to check that from temp sensor terminal (not sure which one so did both) to earth the reading is less than 1ohm..however mine stayed at infinity so open circuit. Not sure of the significance of that or what to check next.

 

Finally did the manual check on the sad by connecting the 12v direct to it. After 5 mins it had closed but not fully. Its cold in the workshop this morning so maybe that stopped it closing fully?  Or maybe there's an issue. Is it worth taking out and doing the 12v test in the oven that I've seen here on other posts? Also should I assume its an airtight seal once closed? 

 

Rest of the tests for section 26 passed. 

 

Feels like some good breadcrumbs and appreciate any and all advice on what to try next 

[mannings 1]

Section  and results scribbled against each line 

[PhilNW 44]

In following sections 20 and 21 have you managed to get the idle revs down to 650 at any time?

 

When you said that that you achieved 950 by rotating the throttle arm with your hand presumably you were trying to force it in the closed direction?

 

Have you had the throttle flap out at any time?

[mannings 1]

No it has never got that low and therefore following the standard set up approach can't be started until I do.

 

Yes if I force close the throttle it will idle at 950 rpm however that's with the bypass screw fully in which doesn't seem right. 

 

And no I've never had it out but this car is a frankenstien of bits so no guarantee someone else hasn't.

Edited April 16, 2023 by mannings

[PhilNW 44]

Section 20 and photo 20.5 and fig 3.13 - sounds like the flap might not be closing sufficiently. 

 

To get the flap fully closed, have you unscrewed the throttle stop screw out such that the the throttle lever is touching the throttle body ? This usually drops the revs pretty low and then screw it back gradually until 650 revs. Air bypass screw should be fully screwed in 

 

 

[mannings 1]

Throttle stop screw is fully backed off so not holding it open at all. It's the most closed it can currently be with the paddle in what's looks like the right angle. 

 

If I turn out the Throttle stop by the stated amount in the Haynes Manual is just goes even higher 

[mannings 1]

Think I might pull out the sad and see if I can get it to close fully in the oven..then buzz out the switch voltage feed to it to see why it doesn't seem to be getting anything when turning engine over 

[PhilNW 44]

Bit bizarre this but 

http://prepparts.free.fr/docs/catalogue/cataloguepeugeot/GB/205N/1/11C51A.HTM

 

Item 2 the oil filler /breather is attached to the inlet manifold with an 8? mm hole/bolt in the manifold, which if I remember right allows air into the manifold if the bolt is missing.

 

 

[mannings 1]

Yes that's right. I've fully tightened so not that. I've tested everyone one of the leak points with carb cleaner and think I've taken out all leaks. So if air is getting in its maybe through the sad I think.

[PhilNW 44]

Might be quicker just to bung up the ends of the SAD hoses.

 

Cant quite get my head round that you can get 950 by "forcing" the throttle lever and what that means. Clearly it is reducing air flow and the AFM is responding.  

 

Is Air bypass screw definitely closing off the bypass system? 

 

Pinking in third, ignition timing? think its 5 degrees on a 1.9 as opposed to 10 degrees on a 1.6

 

[welshpug 1,661]

Is the dipstick and other breathers in good condition?  Any leak here will cause a higher idle.

 

If you can push the throttle closed further than the point it rests then its definitely stopping on the switch not the throttle stop screw.    Or the throttle cable is too tight

[mannings 1]

Dipstick is new and tightly sealed to tube. Oil breathers and filler all new and checked. 

Will check the throttle switch point as well tonight. Plus timing when I get the gun.

Going to buzz out the wiring to sad and temp sensor tonight to see if I can work out what is going on there..

Thanks for the help. Feels like I'm getting close now!! 

[309SRiguy 15]

Has your car got a vacuum advance on the distributor?

I had a split diaphragm which not only made the car run badly through lack of ignition advance, but also let air into the inlet manifold which caused a fast idle.

It might be worth a look if you haven't already checked it.

[Richie-Van-GTi 72 2 Cars]

Also take off and bung the brake servo hose, you could be drawing air through the brake or sunroof system

[mannings 1]

So the prize goes to @welshpug!!! Throttle switch was holding open the throttle body butterfly. Have reset and also taken off SAD to fully test and its bang on with heater working and fully closes on its own with 12v supply. 

 

So after many years she was able to run at cold ~1500rpm then dropping down to a nice 1000rpm once warm with head lights on. Did seem a bit unwilling to start again from hot so needed to give her some throttle and seemed to be fine..not sure what that might indicate.

 

Still need to double check timing and CO mixture to really make sure everything is 100%. 

 

Really pleased and now just final checks before the MoT next weekend.

 

Looks like another gti back on the road..roll on the summer car shows!!!

 

Edited April 22, 2023 by mannings

[mannings 1]

Thanks everyone for the help and suggestions.