After getting my Exige back on the road I’m currently sorting some driveability problems with the VHPD engine.
The engine runs too rich on idle and I’ve got the ‘high idle speed while moving’ problem which I think is related to the first problem.
I’m using the AutoXray 6000 EZ-Scan tool to read out the ECU data.
I know the VHPD engine reacts quite sensible to faults like buggy sensor, vacuum leaks, etc. That’s what I did already:
new temperature, cranking and manifold temperature sensor
new MAP sensor which reads the same values so the old one was fine
new wheel speed sensor and the ECU does shows the correct speed
all new vacuum lines
new iridium spark plugs + coil pack + high tension leads
throttle position sensor has been renewed before and shows plausible readings between 0% and 100%
new idle air control valve (IACV) and hoses
new lambda sensor which shows the typical ‘narrow band’ voltage jumps
balanced the throttle bodies
The following things are ongoing:
renew the manifold gasket as I suspect the old one to be faulty. Spraying brake cleaner on the joint did affect the idle speed.
letting the injectors be refurbished by a local ASNU service
To help tracing the error(s) I’d like to know:
which manifold pressure do you see during idle? Mine reads 65 to 70kPa which I think is to high.
which short term fuel trim do you see while idling. I see -7.5% to -15% on my car which indicates rich running. The car does run in ‘closed loop’ after warming up.
does anybody know a source for the fuel pressure regulator? It reads MKW10016 on its housing and it should be a Rover part.
is anybody running the 190hp ECU together with a cat? The cat and the exhaust are getting really hot (500 to 600°C easily on the outside of the cat and still 250°C at the entry of the exhaust). The high temperatures are probably related with the rich-running problem and might disappear if that is solved.
Which air flow do you see when balancing the throttle bodies using a ‘air flow meter’ (idling at 1250rpm)? Either when running with or without IACV connected.
I couldn’t find any torque setting or the tightening order for the manifold screws in the workshop manual.
I’d like to stay with the standard ECU so going the Emerald route is currently no option.
Any input is highly appreciated.
The ‘standard’ ECU is very limited how it handles the engine… runs it very rich amongst other problems.
I know you said you did not, but I would 100% get an Emerald fitted… it solves all the problems it sounds like you are having and will get the best out of the VHPD with power, fuel ‘economy’ and drivability!
Been there, done that, fitting an Emerald and having it RR tuned properly works!
You can always retro-fit the OEM ECU if needs be when Exige S1 values hit the £100k mark!
The biggest advantage of fitting an Emerald would be that the ECU is no longer a ‘black box’ and you can take full control of the settings.
On the other hand I believe that quite some development time was spent by Lotus to get things like cold start, barometric compensation, closed loop mode, etc. right.
Switching to an aftermarket unit means to do it all over again or just live with a simple map that needs to fit all situations.
As long as there are still faults in the system like air leaks, defective sensors or a broken fuel pressure regulator I need to get those things fixed first.
When my car runs as good as a VHPD might run using the standard ECU and I’m still not happy I will go the Emerald route.
I’m with you and I would not fit an Emerald. I switched to one when my VHPD ran dangerously badly and it was better but it stumbled with things like changes in altitude, weather, temp, even switching the lights on dipped the idle speed and mapping things like canister purge or IACV never really worked well. It had been mapped professionally on a RR and timed with verniers and made 188 bhp and pulled like a train on track. I then fixed the lambda probe and it ran so much better on the standard ECU that I switched back. It was down on power compared with the Emerald but more driveable in varying situations. However, I would use an Emerald if I had a tweaked engine.
The symptoms of my car was that it used to run nicely when cold and then run like a dog when warmed up. I now realise that was when it switched to closed loop lambda control and the lambda probe was giving dud readings. The standard ECU does not switch on the check engine light. That does not sound like your problem.
In my case I know it is possible to get a standard ECU to start first time, idle at 1000-1100rpm, pull from 2000rpm in any gear and not drive like a bucking bronco. My car did none of those when I first got it. It now is almost as tame as a standard K, apart from the noise.
I’m just trying to understand what’s going on. I think the increased idle speed while the car is moving is not a bug but a feature.
The ECU tries to protect the system from damage by avoiding a rich running idle.
It is probably the same feature when lifting the throttle and there is still some surplus fuel on the manifold walls that needs to be properly burned but the airflow dropped to nearly zero. Using the IACV the ECU is able to burn the fuel in a controlled manor and what may also helps to keep emissions low.
Assuming there might be an air leak and the manifold pressure wouldn’t be as low as it should be while idling. As a result a too high value will be taken from the static fuelling table. In addition the fuel pressure regulator does not reduce the fuel pressure enough as it would be necessary when idling.
As the TPS indicates 0% throttle opening the ECU ‘knows’ it should keep the engine at idle speed and uses the IACV and the ignition advance to keep the revs down. In closed loop mode it tries then to trim the surplus fuel using short term fuel trim.
Keith, are you able to read your ECU data to tell me what MAP value you see when your car is idling? The workshop manual states 25 to 40 kPa for the standard Elise but no value is given for the VHPD engine.
Sorry, I do not have a scanner for my car. I have a simple OBD Blue Tooth transmitter which gives me a few values but nothing much. My car does not have “high idle”. If I come off the gas (even at speed) it would fall to idle if I put it into neutral (I will confirm tomorrow when I collect it from being serviced by Gavin). I think you are on the right track, high idle means too much air. Have you checked your IACV works? I had one which was stuck. If it’s stuck (part) open that could be your problem.
I believe, the standard ECU will run the engine with the IACV disconnected and blocked off, so it’s an easy test. If you need a new valve (Bosch part) I believe they are a SAAB part number (maybe GM) and are cheap on ebay.
Hi Keith, thanks for your thoughts. I bought a new IACV so this should be fine. In fact what I was trying to explain above is that the ‘high idle while moving’ issue is just a symptom of
another problem that is the too rich running at the low idle level. I’m pretty sure that blocking the IACV valve will prevent the high idle level but it wouldn’t solve the actual problem.
So most likely the idle will return to a normal level as soon as the mixture at the low idle speed has been fixedr.
Let’s see what is happening once I renewed the manifold gasket, checked the fuel pressure regulator and fitted the cleaned and serviced injection valves.
Knowing the right manifold pressure level on idle would help a lot but it looks like there aren’t too many owners around that have access to an OBD scanner tool.
For me the scanner tool is very useful and it would be very difficult for me to solve such problems without it.
I have just read your first post more carefully. Fix the manifold leak and there is good chance all will be well. High idle will come from a leak. Having a leak will give some odd fuel map results which will affect the mixture.
The injectors have been cleaned and checked by the German distributor of ASNU machines with before and after comparison. They weren’t too bad before but now they are near perfect. He told me that there is zero deviation in the injection quantity between all four of them. This could be only achieved if the injectors have been perfectly matched to each other by Lotus. The guy told me that Porsche used to match their injectors to a level of +/- 2% but stopped it some years ago. So zero percent deviation is quite impressive.
I fixed the manifold gasket by cleaning the surfaces, checked them for straightness and using liquid sealant as the new gasket. I re-balanced the throttle bodies with the IACV disconnected. The car runs now better than before .
The MAP dropped from 70kPa to something like 58-60kPa while idling. The rich running idle stopped and the fuel trim stays around 0% in closed loop mode.
While driving the car the high idling issue stopped but to my feeling it is still not perfect. When I come off the throttle it may take a second or two until the revs are fully dropped to 1250 rpm. And there is an occasional slight stutter when driving at around 2000 to 2500rpm.
Unfortunately there is no other car with a VHPD engine around so I have no clue what is considered to be normal.
I would appreciate it a lot if others would share their experience considering returning to idle and driving at constant lower revs.
that sounds much better. Have you reconnected the IACV and driven it, it will have better idle control.
I need to take mine out at the weekend so I can make a recording of how it behaves. I would say that slowly falling back to the correct idle is normal. Not sure of the time taken, it’s not instant. Have you had verniers fitted? I have them on my car and one cam was quite a bit out, it was set with power runs.
Hi Keith, thanks for your patient replies. It seems to be that you are the only one that still drives a VHPD with the OEM ECU.
I disconnected the IACV just to balance the throttle bodies as the IACV plumbing connects both TB pairs with a fairly big hose.
It should be easier to see the actual unbalance without the hose connecting the pairs.
I reconnected the IACV afterwards so the driving was done with the IACV in place. I will do another test and drive the car without the IACV to see if the slowly dropping revs
are caused by the ECU controlling the IACV.
My car is not equipped with verniers and the pulleys are the non-190 ones (just two slots). It could be that Wilcox who rebuilt the engine drilled the cams to adjust the timing but I have no idea. The timing seems to have a big influence on the drivability as reported by many users. Checking the timing and probably fitting some verniers would be my next step.
Looking forward of hearing your ‘idle report’ and of any other user too
I did another test-drive today to see what influence the IACV has. After warming up I blocked the main IACV hose using a clamp. Unfortunately thing were getting worse and the revs were getting more unstable.
It was interesting to see what happened when I re-opened the clamp while the car was idling. The revs climbed immediately to 3000rpm as the valve was fully open. It took at least 10 seconds until the ECU ‘realized’ that it should close the valve to reduce the revs. So the IACV seems to be controlled rather slow by the OEM ECU.
Fixing the manifold air leak did stop the car from running rich and increased the drivability. But the revs do still stroll around between 1000 and 1500rpm on occasions.
I got the feeling that the throttle bodies do not return to the same positions every time when coming of the throttle. When I push the actuator manually down the revs may drop again a little.
Besides fitting verniers I’m running out of ideas at the moment. Hopefully I don’t have to leave the ‘PROPER S1 Owner Group’ to hang around with the ‘Emerald Sissies’
I could not record anything whilst driving as I could not find a mount and it’s illegal to even touch a phone whilst driving in the UK. It was pretty cold and the car was only dropping to about 1500rpm idle for a while before it fully warmed up. Once warm, it idled at about 1100 with blower and blower with lights on.
many thanks for the effort to create and load up the videos. This s highly appreciated
Your car is idling super stable and returns quickly to the lower idle speed. My car starts as easy as yours and idles fine when stationary even when loads are added. The trouble seems to be the transitions in the lower rev range when coming off the throttle.
As written above I realized that pushing the throttle lever at the throttle bodies by hand may drop the idle again a little. So I increased the existing slack in the throttle cable a little more and that helped noticeable. The drivability in the lower rev range is now acceptable but still not as good as it should be.
Another point: I find it difficult to adjust the idle throttle opening screw to the right amount as it interferes with the air delivered by the IACV.
As I don’t know the target opening of the IACV while idling and I can’t read out the current value from the ECU it is hard to tell what is the right setting.
When I am slowly opening the throttle more and more by turning the screw in I reach the point where the revs start to climb. This should be the point where the IACV has been fully closed. The question is how much to close it again by truning the screw out starting from this point. That’s why I asked in my initial post:
5. Which air flow do you see when balancing the throttle bodies using an ‘air flow meter’ (idling at 1250rpm)? Either when running with or without IACV connected.
Does your car stutter when cruising at a constant 2000 to 2500rpm? On mine car there is still a slight but clearly noticeable stutter when doing so.
My car was idling hot at 1500rpm for quite a while, I assume because it is cold outside. I have not touched the idle speed or balance on my car so I have no measurements.
As I have posted before, my car ran so badly when I got it that it was dangerous. I nearly got t-boned in it with my young son when it bogged down at a junction once. I fitted an Emerald and verniers and it was much better. With the emerald I could see my lambda probe was not working. I changed the probe and went back to the oem ecu and it was better than the emerald.
Does my car stutter between 2000-2500rpm? If I pull away in 5th from about 30mph it sometimes has a very slight stutter. I generally keep the revs above 2500 as it is “off cam” at such low rpms.
I have never touched the throttle bodies so I can’t help there. I think you can reprogrammed the zero setting on the ecu, I expect you have done that already?
I would expect the Iacv software will adapt and not be fixed like the emerald.
If ((TPS == 0)&& (idle-speed < 1100)) increase-iacv();
I like that! I’m working as a software developer so it is easy to unerstand for me. My experience with the unblocking of the IACV leading to the sudden jump to 3000rpm prooves that your code is right.
How do you reprogramm the IACV zeo setting of the EFI ECU? I did not find that. Correct me if I’m wrong but unlike the other Rover IAC valves which are stepper motor driven the one in the Exige is PWM controlled so the ECU should always ‘know’ what the current setting is.
Maybe you are right and I just should not cruise around below 3000rpm. Seems to be not species-appropriate for a VHPD engine.
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