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Discussion Starter · #1 ·
Hi Lads,
My Engine has developed a very annoying idle problem. When the engine reaches operating temp the RPM rises to about 1800rpm then drops to 1000rpm, from then on the revs just go up and down between these. Now when i stop at the lights people think I want to race them as it sounds like i'm pipping the throttle
 
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Discussion Starter · #2 ·
I've just had exactly the same thing with my 1991 VR4 - replaced the ISC valve with a second-hand one from a N/A Galant in a scrapyard and it's fine now. You can check the coils on the stepper motor using a 6 volt supply - see www.dsm.org FAQ's. Mine checked out fine for coil resistance of the stepper motor but failed the 6 volt twitching test.
You're right about it being embarrassing at the traffic lights - I found that switching the air con on to high sometimes stopped it hunting as it opens the ISC a bit more.
 
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Discussion Starter · #6 ·
If not the stepper motor could be faulty Lambda (oxygen) sensor. I believe the EVO VI determines fuelling at tickover and cruise by readings from the Lambda sensor located in the exhaust pipe just after the turbo, and if the sensor is malfunctioning it might effect the evenness of tickover as the ECU probably won't be able to determine the correct fuelling. I don't know whether the same applies for earlier cars.

Steve
 
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Discussion Starter · #7 ·
I've run my VR4 with a FUBAR'ed Lambda - no problems - CE light on permanently. Car ran fine - all in open loop mode - wouldn't recommend it though (just in case) - and I did turn the boost down to 8psi. The ecu always goes open loop when you open the throttle wide anyway. Also it uses the knock sensor to continually vary the ignition timing and learn the best setting - hence the importance of setting the base timing correctly. All these questions about what timing are you running are a bit pointless. All you do by changing the base setting from Mitsubishi recommendations is limit the ecu's adjustment range. Granted if you are using really high boost - 20|PLS| psi then retarding the base setting a couple of degrees extra will let the ecu have a wider retard range to choose from to prevent detonation - but you it will also loose a couple of degrees maximum allowable advance so that low rpm power will be adversely affected.

I'm intending to get a datalogger for my VR4 so I can see the figures for real.

Anyway back to the lambda. It is used mainly at idle and part throttle cruising to fine tune the mixture. When I changed the sensor bits were rattling around inside so it definitely wasn't working. The worst situation is when the sensor is giving the wrong reading and screwing the mixture completely. Have the evos got a lambda test lead spade plug near the ecu like the VR4? A digital multimeter will tell you a lot about how your car is running at idle and on boost.

Check www.dsm.org and their VFAQ's and you'll see that idle surge and the ISC valve (stepper motor) is a common problem.
 
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Discussion Starter · #8 ·
and amp;lt; and amp;lt;Have the evos got a lambda test lead spade plug near the ecu like the VR4? A digital multimeter will tell you a lot about how your car is running at idle and on boost and amp;gt; and amp;gt;

......... yes sort of. The easiest place is probably to the left top of the cylinder head by the cam belt cover (as you stand in front of the car) which is the most convenient place to tap a volt meter in. The Lambda sensor has 4 wires from memory of which two are for the Lambda heater, and the other two for the sensor itself. Like you say a good way to test whether its working or not. You are obviously going to need to know what voltage at cruise/tickover (stoich) should be, and need to know a lot about engine tuning to make a meaningful interpretation of readings under other boost conditions.

Steve
 
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Discussion Starter · #9 ·
The VR4 has a pre prepared spade connector on the signal line under the dash next to the ECU - no splicing required. It's easy to find correct probe voltages from the other Mitsubishi discussion groups on the web. 0.85/0.95 volts WOT - higher is richer - bear in mind that the cheap probes in most cars - ours included are not very linear at anything other than a small range around stoichometric. Best to tune with an EGT gauge too.

Does anyone know what spec the diagnostics port (OBD???) is on evo's 1-3 and 4-6. It's possible that there might be some datalogging software available for laptops and palm pilots. With this you could check the knock sums, injector pulse width and ignition advance too. Home tuning these cars is not a difficult proposition once you learn how they all work.
 
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Discussion Starter · #10 ·
Lightspeed........I think you have to have a very sound knowledge of turbo engine tuning to home tune these cars, unless you want to risk engine damage. I am one of those who don't know so have an Evolink ECU tuned by BR Developments, which allows you to datalog with a data trap of lap/palm top. The tuning module also gives you instant readouts live of all parameters like injector percentages, advance, lambda readings etc. and was tuned using an EGT too. I seem to recall someone on this BBS mentioned you could datalog using the MUTT II tester with the standard ECU.

Steve
 
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Discussion Starter · #11 ·
Steve P......that's the kind of technology we like!!!
Technomotive in the States sells datalogger for VR4 and early eclipses up to 95 - after that the diagnostics port protocol was changed. What other upgrades did you combine with the evolink? Are you still running standard fuel system?
 
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Discussion Starter · #12 ·
Lightspeed........standard injectors, standard fuel pump, standard wastegate, standard boost solenoid, standard turbo, standard BOV. HKS Racing Suction Kit and full HKS exhaust including turbo elbow, front pipe, decat section etc. The injectors run at about 85% at 1.4 bar 7,000 rpm 4th gear. Well within limits. The Evolink uses a MAP sensor so the AFM can be removed from the induction side too.

Steve
 
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