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Spi Inconsistent Idle Issues


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#1 j.gerbes

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Posted 08 July 2018 - 03:34 AM

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.


#2 hungdynasty

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Posted 08 July 2018 - 04:55 AM

>>>>Crankshaft position sensor

Even more unlikely as the car runs well and does not knock or misfire.<<<<

I had idle problem especially when engine was hot, changed crank sensor and problem gone.

#3 Milton

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Posted 08 July 2018 - 07:37 AM

Adjust the stepper motor as per the Haynes manual

#4 j.gerbes

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Posted 08 July 2018 - 08:02 AM

Adjust the stepper motor as per the Haynes manual


Thanks for the tip. Does that require a scan tool? I don’t have a Haynes manual yet

#5 j.gerbes

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Posted 08 July 2018 - 08:03 AM

>>>>Crankshaft position sensor

Even more unlikely as the car runs well and does not knock or misfire.<<<<

I had idle problem especially when engine was hot, changed crank sensor and problem gone.


Interesting. I’ll fit the new crank sensor tomorrow and let you know if that helps

#6 viz139

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Posted 08 July 2018 - 11:13 AM

Coolant temperature sensor faults are often the connector and not the sensor itself. As the problem develops with heat I would check the inlet manifold gaskets for air leaks.  Are your fault codes current or in the ecu history? ( clear codes and run again).



#7 Milton

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Posted 08 July 2018 - 11:44 AM

Adjust the stepper motor as per the Haynes manual


Thanks for the tip. Does that require a scan tool? I don’t have a Haynes manual yet

No. You can download procedure from the internet.

#8 Milton

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Posted 08 July 2018 - 11:46 AM

Adjust the stepper motor as per the Haynes manual


Thanks for the tip. Does that require a scan tool? I don’t have a Haynes manual yet

No. You can download procedure from the internet.

Have a look at this link,there is alot of info regarding this on this forum

https://www.google.c...mobile&ie=UTF-8

#9 j.gerbes

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Posted 08 July 2018 - 11:48 AM

Coolant temperature sensor faults are often the connector and not the sensor itself. As the problem develops with heat I would check the inlet manifold gaskets for air leaks. Are your fault codes current or in the ecu history? ( clear codes and run again).


Thanks for the tips. Is there any way to check the connector without removing the whole inlet manifold. Also, how many inlet manifold gaskets are there? I thought there was just the one gasket that was shared by the exhaust manifold.

The codes were in the ECU history and have been cleared. Unfortunately, it would require me to visit the mechanic to check which codes have returned.

#10 j.gerbes

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Posted 08 July 2018 - 11:57 AM

Adjust the stepper motor as per the Haynes manual

Thanks for the tip. Does that require a scan tool? I don’t have a Haynes manual yet
No. You can download procedure from the internet.

Is this the procedure? If so, I’ve already done this.

http://www.theminifo...-stepper-motor/

#11 Milton

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Posted 08 July 2018 - 03:07 PM

Adjust the stepper motor as per the Haynes manual

Thanks for the tip. Does that require a scan tool? I don’t have a Haynes manual yet
No. You can download procedure from the internet.

Is this the procedure? If so, I’ve already done this.

http://www.theminifo...-stepper-motor/

Yes, thats the one

#12 viz139

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Posted 09 July 2018 - 12:59 PM

The main inlet/exhaust manifold gasket which is specific to injection cars and one between the manifold and trothel body. You could also check that the locating rings are between the manifold and head. You should be able to unplug the temp sensor plug and examine it in place.



#13 genpop

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Posted 12 July 2018 - 06:04 AM

Do you know this page?:http://alum.wpi.edu/...c-protocol.html

newer software is here:github.com/leopoldG



#14 j.gerbes

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Posted 12 July 2018 - 09:23 AM

Do you know this page?:http://alum.wpi.edu/...c-protocol.html
newer software is here:github.com/leopoldG


Hey, yeah I have seen that guide. It looks promising but getting the parts required for the cable seems costly (unless making them in bulk).

Also, I was told by a seller on eBay that this cable + software combination doesn’t have all of the functionality of the ARC scan tool. Is that correct?

#15 j.gerbes

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Posted 20 July 2018 - 06:10 AM

Update on this topic:

Replaced the coolant temperature sensor and inspected the connector and wiring. The sensor looks relatively new and the wiring looks fine. Connector pins are clean and have no corrosion. No improvement.

Checked all breather tubes for vacuum leaks. No obvious issues.

Checked the operation of the stepper motor when turning the key on and off (without starting the car). The stepper motor is not indexing correctly and instead just shudders slightly.

Replaced the stepper motor with a brand new one. No improvement.
The new one also won’t index correctly.

So the issue apppears to be the signal to the stepper motor.

As the stepper motor is directly connected the the ECU, my thoughts are that it is either a wire is loose/broken or there is a fault inside the ECU itself.

I’m going to remove the ECU tomorrow and use a multimeter to continuity test each of the 4 phase wires from the ECU’s connector the the stepper motor.

Any suggestions at this point would be appreciated.

Attached Files


Edited by j.gerbes, 20 July 2018 - 06:11 AM.





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