fast idle volvo 1800e D-Jetronic fuel injection

Hi First post I know there is a lot written on this topic having read and tried the troubleshooting I still have the problem.
1. Fast idle of 1800-2000rpm which increases as engine warms to approximately 2500 there is no variation (hunting). IThe following statements are true to the best of my ability. The problem remains after the following
There is no air leaks all hoses replaced intake manifold checked for cracks and gaskets replaced all fuel injectors replaced new harness new seals sprayed carby cleaner to check for leaks and change in idle speed with no affect. The throttle position checked and TPS checked per instructions found on site. Previously set timing at 10Degrees BTDC at 800 RPM. I managed to get RPM to this by making a cap and almost fully occluding intakes (copied original tool as per manual). So before I start all over maybe someone can provide a logical path given the above. Have I made a mistake ?? why does the manual require the intake to be almost fully occluded to get an RPM 800 for timing. Any help before I start all over again appreciated. Rob
 

Hi Rob,

welcome to Jetronic.org .

Your can engine only do hunting if you have ECUs 0280000009 or 0280000017 . Later ones have no over-run shutoff which is what principially causes the hunting if idle-run switch in TPS is closed as well and rpm goes too far up.

Main suspect for high idle is AAV and false air. AAVs tend to hang in cold open state and then this increases idle when engine warms up.

I did not understand what cap you made.

 Thankyou for the prompt reply and also the quality of your articles.   . I have attached 2 photos showing cap as per workshop manual. I dont really understand this as idle speed is 900 normally so unsure why such a large air restriction (usingcap )is necessary to get to 800The AAV is removed as not functional and inlet outlet blocked off ( I don't require cold start function where i live and a replacement unit is very expensive tried to unseize mine without success). Before commencing diagnostics / fault finding again I thought about buying a smoke machine to test for leaks on the intake manifold as is. Failing that I will follow your description starting with engine timing spark and fuel. However I wondered how big a leak (air flow /size of hole) would be necessary to allow sufficient air to boost idle to 2000 RPM

Thanks Rob

Hi Rob,
thank you for the information about this very special cap.

There is not much extra air needed to let the idle rise.
The  Volvo manual says " If the speed cannot be reduced sufficiently, the basic setting of the throttle valve must be checked." - did you do so?


You said  you don't need a cold start system - but the AAV is needed during all  the warming-up-process of the engine - where extra air is needed and extra fuel, too. The fuel is given by the ECU - maybe one has given the extra air to the engine by a manipulation (maybe just by opening the throttle 'a little bit' at the screw).
With the engine warming up - the extra fuel isn't given anymore - but the extra air isn't reduced and the idle is rising when the engine warmes up.  

The throttle shaft [/url]tends to wear out (and give extra air), too... maybe it has to be replaced

Regards
Norbert

Yes I see your piont about the AAV however very expensive will revisit mine and see if I can repair it ( frozen shut). The problem may be how much air and how big a leak ,the throttle shaft has a little play  less than ? 0.1mm play in it,the throttle is currently adjusted so it is fully closed  at idle. Will try the smoke test then go from there. Will I keep you updated?
Rob

Hi Rob,

if I understand this Volvo specific throttle flap adjustment correctly, it has to be done with a fully closed AAV. If yours is stuck open, it makes no sense. Overhauling an AAV is not that horribly expensive if you do not go to this provder . Volvo owners tend to continue with leaking or stuck AAV. When it leaks coolant, it can get between piston and cylinder in AAV and dry out. Then pistonsits extremely tight and it is very risky to remove it, especially with Volvos fragile small AAV housing.