Hi all,
I'm having some idling trouble with my SPI mini and would greatly appreciate any help.
Background
I purchased my mini last November and found that it would occasionally stall when returning to idle. I checked the vacuum hoses and found that several had split elbow connectors. I replaced all of the vacuum hoses and the fuel trap, which fixed the stalling issue, but left me with an inconsistent idle speed.
On initial start up, the idle speed is generally very low, just turning over really. After a short drive, the idle creeps up and can eventually get as high as 2,000 RPM.
The car runs perfectly, never knocks, never misfires. It just won't idle consistently.
The spark plugs, leads and coil pack are all <6 months old.
It has the standard air filter housing with a new K&N filter.
Fault codes
- Throttle position sensor faulty.
- Coolant temp sensor faulty.
- Air temp sensor faulty.
What I have done so far
- Replace all vacuum hoses and fuel trap.
- Ensure that the hoses weren't pushed on too far (which would block the connectors).
- Replace the TPS (throttle position sensor) -- this was damn hard to find a replacement for.
- Reset the TPS (ignition on, car not running, press accelerator all the way 10 times, start car).
- Reset/reboot ECU (disconnect battery for a few mins, reconnect, start car, let idle for 10 mins).
- Checked the throttle cable, it moves freely and doesn't get stuck. Also, the cable has slack while the car is idling high.
- Adjusted throttle cable (using this guide).
Possible causes
After doing some more research on this forum, here's what I think the cause might be:
Coolant temperature sensor
Apparently this sensor can have a big impact on the car's idle speed, plus there was a fault code logged for it. My hesitation to replace this sensor is that it's a major job (for a novice like me) and the car's temperature gauge works perfectly (on min when cold, just below white line when at operating temp).
Stepper motor
The stepper motor is another likely culprit. Given that the throttle cable has slack while the car is idling fast, the stepper motor is what's controlling the idle speed.
I have found that the plunger off the stepper motor is extended too far when the car is idling fast, and physically pushing it back returns the car to a proper idle speed.
Lambda/oxygen sensor
Least likely in my opinion, but the lambda sensor does effect the fuel/air mixture and could cause the car to run rich or lean.
Crankshaft position sensor
Even more unlikely as the car runs well and does not knock or misfire.
Vacuum leak
I have ruled out the vacuum hoses and fuel trap as being an issue, but their could be a vacuum leak elsewhere in the system.
ECU
As much as I'd hope this isn't the case, the ECU could be faulty.
Next steps (?)
I have purchased replacements for the coolant temp sensor, stepper motor, lambda sensor and crankshaft position sensor. I figured they'd be good to have as spares even if I don't end up replacing them now (especially after the difficulty I had to get a new TPS sensor).
Unfortunately I do not have a scan tool for my mini. I'd like to buy one but they don't seem to be readily available and are prohibitively expensive. I've tried to find someone local (Auckland, New Zealand) that has one, but no luck so far (other than my local mini mechanic at $75NZD per scan).
I'd like to replace the coolant temp sensor next, but feel that it may be out of my realm of expertise.
Any advice you may have for me would be greatly appreciated!
Edited by j.gerbes, 08 July 2018 - 03:35 AM.
