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Terry1600

Trying To Find High Idle, High Runing Revs Issue 1.6I

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Terry1600

after trying out an afm, ect sensor, sad valve im looking further into this.

 

if i set the idle screw out enough to get the car started without stalling, after a few mins when warm the idle will be over 2.5k

 

i get out and tun it down to about 1500 where it will hunt from 1500 to 500.

 

the car had a starter just before i bought it, ive had this issue since day one.

 

ive stripped down the intake manifold and have noticed that there is 4 take offs from the bottom of the throttle body, 2 water and one for the dizzy advance, is the other one blind? ive tried blowing down it but seems to be plugged.

 

also when i took the fuel rail feed off ive never ever had so much pressure come out of one of these, is that normal because it literately when i broke the seal popped and loads of fuel came out even after being sat for a while.

 

cheers guys for the help.

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Terry1600

ive got another throttle body upstairs, the brass screw on that one is sticking out unlike the one thats on it at the moment, that one has a sunken brass screw and hasent got the extra takeoff this one has

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Telf

To my mind its an unmetered air problem.

 

I'd carefully check every single hose for splits and cracks- especially if there are any tight bends etc where the rubber often perishes.

 

Also make sure the bolt on the inlet manifold that holds the oil filler body is tight- if loose it lets air straight into the manifold.

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Telf

fuel rail has a pressure valve that opens at between 2.5 to 3 bar if memory serves. in my experience the fuel pressure usually reduces if its been sat for a while but I'd expect pressure to be there if I'm taking the rail off.

 

Think that's right- I'm sure one of the guys will correct me if its wrong.

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Terry1600

fuel pressure just seems sky high, i looked at the return pipe and its bone dry, shouldnt it be constantly returning the extra pressure?

 

just waiting for a new intake gasket to arrive, i have checked all the pipes, nothign seems to be perished or broken

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Telf

well it maintains the pressure at 3 bar and opens to return fuel to the tank over this level.

 

if you want to test it see here:

 

http://forum.205gtidrivers.com/index.php?showtopic=143783

 

I've had a similar problem with my 205 in the past- I'm sure many folk on here have had idle issues. Mine sat around 2500 revs. It was the Inlet filler bolt loose on one occasion and a slipped cam belt on another.

 

The slipped cam belt was out by 2 teeth - that however had associated mis-firing and horrendous overfueling that literally blew 2 back boxes to bits..

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Terry1600

ah yeah ill check the timing aswell cheers

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Telf

After you have put it all back together make sure its all set up properly, I've just pinched this setup procedure from another thread on here. I've used it in the past to get a reasonable setup.

 

1. Ensure your spark plugs and air filter are clean, injectors working as expected and fuel of desired choice (97 oct+) is topped up

2. Clean the throttle body fully and double check the idle screw and passageway is clean, and the same for the stop plate on the throttle arm where it meets the throttle stop screw

3. Warm engine up (until rad fan kick in)

4. When the engine is warm and still running, squeeze one of the SAD pipes, if the engine drops off then your SAD is stuck open and will need fixing first, if all is ok then just stop the engine

5. Turn AFM air bypass screw fully in and then turn out by 7 full turns

6. Turn throttle air screw fully in

7. Start engine and set throttle stop screw to 600rpm (650rpm on 1.6)

8. Turn throttle air screw out until RPM achieves required idle speed (900rpm +/-50rpm)

9. Blip the throttle a few times

10. Richen the mixture on the AFM by turning the screw by no more than 1.5 turns either direction of in or out (MIN 5.5 turns out to MAX 8.5 turns out, all from fully closed/in) until the desired CO reading is achieved (1% - 2%) which will raise the RPM

11. Blip the throttle a few more times

12. If required, turn the throttle air screw in until the RPM is lowered back down to required idle speed in step 5

13. Stop engine and adjust TPS to idle switch stop position (pin 2 and 18 continuity)

If you've messed around at all with your distributor that may need setting to.

Edited by Telf

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Terry1600

cheers for that, ive also noticed that when im cruising at 2000 rpm, when i come to a stop it will stay there, i have to blip the throttle to get it to come down again, then it will slowly rise to about 1800

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Rob_the_Sparky

Have you looked at the SAD yet? (Supplementary Air Device)

 

Seems like the most likely candidate, to have high revs you must have air and the SAD is meant to shut down the air as the engine warms up. If it is stuck then you would get your symptoms. Unfortunately it lives in a really awkward to get to place under the distributor...

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welshpug

SAD wont cause an idle this high, it will only make it idle at 11-1200 and not lower to 900-850 when warm if its not closing, this will be poor setup or condition of everything else.

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toolie72

Blipping the throttle to bring revs down used to be an indication of a failing afm-it’s like a crackling volume control in reverse

Only way to check is to try a known good one

 

That’d be my first guess

Nb cold start won’t show as working if engines not set right, it’ll be masked by the engine struggling, when everything’s ok-it’ll “magically” work again!

Afm simply tells ecu how much air engine wants-anything spurious here and ecu doesn’t have a clue, add that to the “issues” most of us have on these cars and we end up going round in circles

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Tom Fenton

Blipping the throttle to bring revs down used to be an indication of a failing afm-its like a crackling volume control in reverse

Only way to check is to try a known good one

 

I'll disagree here. As I once read in an ECU write up, you can't send air down a wire. Ok modern stuff with an idle air valve yes you can, but it holds true for a Jetronic 205 that you can't. Or in other words, the ECU can't control idle speed, that is dependant on air flow. All it can do is make things fuel wise richer or leaner depending on what the various sensors tell it.

 

Blipping the throttle and the revs dipping means either a dirty or sticky throttle butterfly, or the throttle switch is going intermittant and not making every time, or a combination of both.

 

I've not worked on an 8v 205 yet that wasn't improved by removing and thoroughly washing out and cleaning the throttle body and breather pipes with degreaser.

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toolie72

Is leaner not the same as more air for a given volume

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Tom Fenton

Not really no. Engine speed on a petrol engine is governed by airflow.

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Telf

Just re reading this and thought of a couple of other times I've seen this:

 

1.Oil filler cap cracked at the hose attachment point (either side! - look out for hairline cracks)

 

2. Oil cap o- ring perished

 

Again unmetered air entering the system

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Terry1600

ive stripped down the intake and inspected every pipe, i couldn't find anything so i changed the gasket anyway. the only think i can find is that the vacuum advance on the dizzy is wide open, ive took the pipe off it and put a screw in it until i get home.

 

car seems to idle a lot better from turning the key, going to take it for a quick drive see if anything else is still happening. ill report back in a bit, cheers guys

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Terry1600

Ok, found the issue in the end, vacumm advance wide open on the dizzy dosent help, bur ive noticed.

 

1. when cruising, the car will hold 2k rpm even when my foot is taken off the throttle, a blip will lower it but then it comes back up.

 

2. when the revs are high i adjust the throttle brass screw to lower them, runs fine but then when i start it from cold i have to open it enougth to allow to warm up and then close it a bit again.

 

what ive found is that after i took my throttle body off, i couldn't really tell as it was dirty but the throttle plate has come loose and has been riding on the shaft, easy fellas i was thinking exactly the same thing. cant be good. also theres 2 vac pipes on the bottom, one for the advance and another what seems to be for an emissions canister from what i can find, even though i blow down this it seems blocked of, but so does the pipe that allows the brass screw to breath.

 

anyways ive cleaned up an old throttle body i had up in the loft and now she purrs like a kitten, i can start her up with no pedal help and she idles at 1000k dropping just below with headlights on and the fan for the engine on.

 

i will report in the morning what its like to start from stone cold, wish me luck, cheers for all the help so far!

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