I wonder if anyone might be able to help me. I have a UK M101 Sirion/Storia with the K3-VE2 engine in rally II spec. Its a project I bought for a couple of hundred pounds but needs some issues attending to. The current bugbear I have is that the idle speed sits very high.
switching on from cold, the idle starts at ~1200rpm. it rapidly rises to 1500rpm when coolant gets above 40c and sits at 1800rpm up to 74c. At 75c, the idle starts surging between 1200rpm and 1800rpm in 3-second bursts. I believe this is down to the ICV being faulty and the ECU trying to compensate for the high idle by cutting power to the injectors to try and bring it down.
Much like the thread here Idle help - with the AC turned on, the idle stabilises at 1500rpm steady. Still too high, but stable at least!
I have replaced the throttle body with a second hand unit, this didn’t help the issue at all - frustratingly! It was slightly worse, with idle sitting a little higher than previously, so I have gone back to the original throttle body unit.
I have access to diagnostics which shows the MAP sensor to be working largely correctly, it displays 100kPa with ignition on, but engine off. This drops for between 34 and 38kPa with the engine running. The diagnostics showed O2 sensor S1 (pre-cat) to be faulty so this was replaced, and I now get correct voltage and short term fuel trim readings while running.
I have replaced the throttle body and inlet manifold gaskets as a precaution, and spraying aerosol brake cleaner about with the engine running makes zero difference to the idle speed, suggesting there is not an inlet air leak after the MAP sensor.
I get readings from the throttle position sensor when I press the accelerator/gas pedal so believe that is working correctly. I have ensured that the accelerator cable to the throttle body has plenty of slack in it and is not overtight. the throttle butterfly closes as it should when the accelerator pedal is not being depressed.
With the engine running, I can reduce the engine speed to approx 1000rpm and keep it stable by using my finger to block ~70% of the throttle butterfly bypass duct. Closing it completely (unsurprisingly) causes my engine to stall.
This suggests to me that my throttle body idle control valve (ICV/IACV) is either jammed or broken entirely, however I get the exact same behaviour from my spare throttle body. I have ordered a replacement ICV housing and stepper motor which ought to be here in the next week or two and I have a fresh gasket for the Throttle body/ICV housing joint.
In the mean time, I have been using my multi-meter to test the wiring to the ICV, this has 3 pins. on the loom side, I am getting 12v between pins 1&2 and 2&3, but zero volts between 1&3. This suggests to me that the loom is providing power to the ICV.
On the ICV side, I measured resistance. I see a resistance of 47.2 in the 200k Ohms range between pins 1 & 2, and infinite resistance between 2&3 and 1&3. On the second throttle body, I get a reading of 61.7 in the 200k ohms range between pins 1&2 and infinite on the others.
Finally (in desperation!) I manually moved the idle control valve to force it further open to see what effect this had. The result is that the idle speed is now higher than before, with idle sitting at approx 2050rpm now, sitting stable until it hits the magic 75c coolant temp before the surging starts.
I believe that the ICV on both throttle bodies are bad and jammed in one position. either the stepper motor is broken/burned out, or the ICV is gummed up to the point the stepper motor cannot overcome the friction and close the actual valve.
Frustratingly, the valve assembly is held in with 5-lobed ‘security’ torx screws. I’m waiting for a set of these to arrive as I only have 6-lobed torx bits to hand. Once they do arrive I will strip down and clean the ICV assembly and set the valve to nearly fully close manually, rebuild it all and see what the idle speed is like then. I hope this will result in either the ICV coming back to life and adapting on the fly as it should, or at least having a fixed, lower idle speed as less air will be able to bypass the throttle body butterfly than at present, with the valve jammed wide open.
Is there anything else I should be checking in the meantime? I have diagnostics computers and most common tools at my disposal.
I cannot drive the car on the road as the MOT is expired. I can move it about on my private drive which is ~30m long though.