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BobG

IAC Valve replacement

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post-3968-0-55853900-1363283537.jpgPrevious story was that last year the alternator died so I
tried to remove it and struggled. Then as the IAC had also packed up previously
(I had been running the car with it disconnected for a year seemingly with no
ill effect apart from it not ticking over until engine was warm) I decide to
remove the plenum to change the IAC and also hopefully achieve better access
for the alternator.

 

This proved to be completely wrong and I must still return
to the underside to attend to the replacement of the alternator. However I have
now replaced the IAC and returned the plenum to the top of the engine. Problems
were the dump valve tee pieces- you have to sit them at 45 degrees between the two
pipes and then force the plenum downwards (only way I could think of doing it) so
that the tee pieces end up horizontal and equal distant along the two pipes. Also
kept having trapped sensor wires between the mating surfaces of the plenum and inlet
manifold.

 

I have also figured out a way of supporting the return coolant
hose that otherwise flaps about on the top of the bell housing, by extending the
bolt holding the slave cylinder to its bracket and using a p clip on the extended
bolt with a nyloc nut. I don’t know how Lotus originally did this, or how they secured
the turbo oil pipes which also in the same area seem to flap about and vibrate.


Anyway, assuming the alternator can be replaced Esprit will
be back on the road by Easter

 

Rgds

Bob G



 

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I have two  wooden 2 x4 's cut to the right length to support the plenum and then use a mechanics mirror to move wires around and plug in the connectors. Still a challange but better.

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not sure who told you that the alternator is under the plenum ?

 

..anyway, the water line can be fitted to the bellhousing, if you look there is a mounting point (hidden behind the aluminium water line in you picture)

 

..if the water hoses, the braided ones from each turbo are positioned right there is enough room to fit the t-piece water connector just there onto the bellhousing, as it is not in the middle so fits peffectly ..you can even use a braked to hold it more in a distant position 

 

 

..there is also not a big problem to refit the plenum, if you simply keep in mind that the aluminium ducting that comes from the turbos either side is only held in place by a M8 screw (13mm hex) each side, as it sits on the turbo with a flexible hose too

-so undo the screws there (mounted in the heads rear face each side) ..tilt the cast aluminium ducts to the sides, push the hoseclamps an the factory rubber connectors/or dump valve connectors (depents on the grade of engine tuning) as far onto the cast aluminium as it goes .. place the plenum chamber evenly on the marking dots (some smallish pins there on the intake ducts of every cylinder head)  ..and there you go

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Thanks for your comments

 

I didn’t know the ducting up from the turbos was easy to
move and slide further out- I looked before and the other end appeared buried
behind much wiring etc. But your comments good- should have asked before! And I never thought of a mechanics mirror, sounds like essential kit for working on this engine.

 

And the bits of wood- that was the only way I got the plenum
off in the first place, again because of the dump valve tee pieces.

 

As the engine has not run now for a year, when it is all up together
with new alternator I want to turn the engine over before she
fires to get the oil up- what is best way of doing that? Pull the wire off the crankshaft sensor
for instance?

 

Also, and as the battery has been disconnected all this time
is the alarm going to play up now- perhaps because its internal battery has now
gone flat?


Cheers

Bob



 

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if the NiCd-Accu inside of the siren is rotten/old it would probabbly have a ditch in it anyway after a long time without a charge impulse from the main-system.  ..so it will not react anymore on a shoutoff from the main battery system (the main one that powers the car) ..means the siren can only sound as long as the car battery is connected to the car system

 

-do you know what the last state of the system was ? ..if it was 'not armed' there should be nothing to hear now, even after a long time

 

 

-for cranking with the starter, simply undo the fuel-pump relay (both ones)  ..you will not have fuel-pressure now in the rail, if ignition key is turned *on* (as the pumps do not prime) ..and no injectors.   means with a full charged battery you can crank up with the starter as long as it does not get to hot, and until you see some oil-pressure build up

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Thanks Gunter, alarm was not armed when I disconnected the
battery last year- assume the nicad is in the alarm box close the big engine
ECU?
 

Thanks for the advice on the fuel pump relays- just what I
wanted.
 

Cheers


Bob



 

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as you can see from my post to ´'alarm iren' within here in the v8 section it is in the siren itself ...that is also possible what causes a notable drain in the main battery system, if the Cobra arming-sytem constantly tries to recharge the faulty package there

 

 

...in the US there is this sir-lotus who tries to sell fob replacements and overrun-keys to everyone there in US with an newer series Else..

but I hope he will some day just tell us what is the difference in all those various siren numbers there, even if it means he would make less mony with selling new sirens ;)

 

 

*have posted the pump relay poiions withinhere in a other post, with pictures from the parts lst, so just take a look there

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Effect of new IAC valve:

Finally got it all together again with brand new IAC valve installed and engine started. However it ran immediately at 3000 rpm, was pleased I had turned the engine over without the fuel relay in (been idle for 12 months) to get the oil round. Engine was rattly initially then settled down.

Important thing is that after the fourth start up the revs settled down to less then 1000 rpm but it still does what it did before- when you blip the throttle the revs take a long time to come back to less than 1000 rpm.

I am assuming this is a characteristic (weakness) with the ECU.

I am also assuming that as I ran the car for two years without the IAC connected the ECU went up to maximum boost signal for the IAC and then had to “learn” to signal it properly now it is reconnected.

Be interested to know whether everyone’s car behaves like this of whether I may still have a fault somewhere else.

Bob G

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'in town'  (as you more cruise with slow shifting than race there)  ..if I have to change a gear and go on the clutch the rpm level goes around 500rpm to 800rpm higher than it was just in the moment before (so based on the everytime different gear that was engaged, from 1000rpm to 1800rpm as soon as the clutch is open, or from 2000rpm to 2500rpm and back to the lower rpm as soon as the turbos slowed down  ..all with different roadspeed situations)

 

..as more as you change gears in higher speeds with overall higher rpm-level as less notable is this 'jump' there

 

Cold start on the other hand, with higher idling for some times workes as normal, and with a hot engine everything as it should too  ..engine still has the original IAC valve fitted, but the plenum was *off* severall times in engine live, idle valve was cleaned within this process once

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Thanks Günter, so you are saying that when driving the ECU will hold the revs up higher,  based on a whole load of inputs to the ECU and therefore the IAC, including normal or fast driving, the gear, speed and revs. This makes sense to me as it will help the next gear if the revs haven't dropped too far back.

 

However sitting in a garage at tick over, why would the revs take so long to come back down to 800rpm? Assuming that you cleaned your idle valve (IAC) in a solvent as you previously described. And it can only be these two components the IAC and the ECU- there is nothing else that would impact on this.. or is there... an induction leak maybe?

 

Cheers

Bob G

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some say this is just the 'bad layout' design of the intake system and turbo arrangement vs. factory mapping, so I deal with it and do not worry ..it just lifts up the rpm slightly if I shift (clutch open) ..as there is a short delay on turbo reactions time (spool up/down) in my car anyway 

(no blow off or such things installed, simple aftermarket wastegate capsules and a little to tight calibration ..for a more firm feeling on acceleration)

 

*************

with car 'sitting in garage', and even under cruise mode (see boost/MAP signal on data-stream varying to throttle positions)  our 918 twin-turbo engines are still running most of the time like natural aspirated ones  ..what means the MAP level is notable below BARO-level  ..as said, even if you drive the car in town in a normal way, there the boost (MAP-level) is only rising over the sea-level atmospheric pressure [100kPa]  if you are way over 30%TP or so  ..

 

..so if you have the engine idling the IAC-valve offers the air bypass and holds idle rpm to a specified level.

If the throttle linkage ist sticking ..or simply the plenum is not fully 'sealed', or a hose for vacum servo assist or emission-evaporation is brittle and leaks ..with those last three points the ECM would try to 'work against' an suspicius air flow, but as it has no control over the characteristic and cause of this additional airflow to the intake there is some irritation .. that's how I would see it.  Does this make any sence for you ?

 

..try it with flamable brake cleaner (be cautious on the hot exhaus manifould on the engine sides!!)  ..try to spray some brake cleaner in a fine mist all under the plenum, from front or rear, and between the gap there that is left & right next to the plenum chamber (where you can see the injector rail partly)   ..is there any reaction/ rising idle ?

..or even more hesitation now to drob down into stable idling ??   ..as said, under most conditions the engine sees a negative pressure in the plenum chamber or at least next to the trottle chamber .. so any leak around the plenum chamber would be indicated by brake cleaner that gets into the combustion process now 

 

.. you can also spay onto the wastegate-regulator valve, this sits RH side of engine bay (sidewall, but be carefull not to set the engine bay under fire..)  ..this is simply a type of three-way valve  -it normally vents wastegate capsules to atmosphere, and if there is to much pressure in the plenum the MAP level is routed into the wastegate capsules, forcing the internal flap on every turbo to open (therefore reduce exhaust flow on the turbine wheel)  -if now this  *vent* port is not totally sealed under idle/cruise condition (if you cant find the 'thirt way' ..the small foam there covers it normally)  ..ambient air could enter the plenum chamber and the small red plastic pipe would work like a small bypassing line to supply more air than expected.

 

Easiest test would be -pull out the plastic pipe there next to the RH trottle body/intake ellbow  ..does it show now even more delay/high idle ..or is it as it was before  ??

 

..if your plenum, is sealed, no vacum takeoff hoses broken and the small red plastic line for wastegate actuators is not the cause for your problem -other easy test would be to crimp off the takeoff port there for the IAC-valve with a clamp, this blue hose (use a soft clamp to not harm the blue silicon hose)   ..this way you would do what the IAC normally does, as this is the feed for the Idle air

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think WayneG and other Forum Members in here have 'data charts' available for comparision, so you could also compare idle rpm, ignition timing and Idle-valve percentage for normal ambient temperature (factory set engines  ..)

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The ECU increases the IAC percentage to about 62% while at cruise and will slowly drop the percentage as the car comes to a stand still. If you start the car on a hill and let the rpm settle down to about 800 rpm and then coast down the hill the rpms will immediatly pick up to about 1200 rpm, as soon as the ECU sees the VSS pick up. I have no idea why lotus did this or why they designed the ECU to hold the rpms up between shifts. I've heard all kinds of rationale for it, but none make a great deal of sense. I suspect your ECU/car is behaving correctly.

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That's really helpful. And I assume it does learn after being reconnected- I drove the car on weekend and initially it would not tick over less than 2500 rpm! Then slowly it came down to 800 but only when car stationery. I am hoping next time it will be less initially and a developing trend.

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Hopefully this question is somewhat on topic.

In the photograph of the first post, there's a small diameter red plastic tube traveling from the right side engine bay wall to the rear of the plenum. Is this not the vacuum control tube to be tapped for the BOV, dump valves? If not, what's the purpose of the tube? I've looked at the service and parts guide and still cannot ferret out what this is...

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The red hose indicates the control signal line for the wastegates. The end exiting from the plenum in your picture is on the plenum side of the throttle plates and is the source of the vacumn/boost signal for the frequencyvalve which controls the wastegates. I prefer to use the vacumn/boost signal from the front port adjacent to the big port serving the brake vacumn booster for the BOV's.

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The attached photo shows my engine all rebuilt, and the BOV vacuum boost pipe is indeed tee'd into a spigot on the front of the engine close to the brake servo outlet.

 

I am still suffering from high tick over and have run out of options - can find no evidence of induction leaks and have tried all the helpful suggestions, going to  have to  turn to expensive advice as next step. :no

 

 



post-3968-0-66220300-1368036541.jpg

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You could block or pinch the blue hose going from the right compressor duct to the IAC valve under the plenum, then no air should get to the engine except by the throttle plates. If the high idle is still there, block the BOV vacumn line and then the line to the vacumn brake booster.  What is the vacumn level at idle?

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Yes many thanks all sensible thoughts and I do have a vacuum gauge. Will try this in next few days

 

Cheers

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I had a terrible high-idle problem on my 2003 (2500 - 3000 rpm) that occurred whenever I did wide-open throttle then returned to a normal idle speed after turning the engine off and waiting 1-2 minutes before restart.

 

SInce I was under the impression that only an air leak could effect idle speed, it took me quite a while to finally discover that the cause was actually the secondary injectors. One or both would stick open on WOT (about the only time they are used) and wouldn't close until the fuel pressure bled off.

 

I'm not sure all of what the ECU was doing with the extra rich mixture but the effect was a very high idle speed.

 

So whenever I hear of someone else with a high idle speed (tick over to you British) I feel compelled to tell my story and encourage them to check the secondary injectors for leaks!

 

I diagnosed the problem by first unplugging the secondaries. When they never opened, they never leaked and I could do WOT/full boost and return to a normal idle. I then cured the problem by simply cleaning them with carburetor cleaner.

 

So I would definitely recommend checking/cleaning the secondary injectors. They are so easy to service.

Edited by billstr

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Please disregard my post about secondary injectors and their effect on a high-idle. I thought cleaning these solved my high-idle problem but it appears it's not yet solved. Sorry if I mislead anyone.

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