Wont Idle when warm - 1.6 Sigma

[LewisAV]

Hi All

When cold car runs fine. Once warm the car will stall. Checked so far.....

1. Air leaks/the three bungs. All good

2. TPS - Sitting at 4.2. All good

3. Lambda - All good

4. Earths - All good

5. Spark plugs & HT - All good

6. Idle position - All Good

Has anyone had the same issue or heard of this before.

Thanks in advance

Lewis

[aerobod - near CYYC]

How did you confirm the Lambda sensor is working? Assuming it still stalls when the Lambda sensor is disconnected from the ECU at the 4-pin connector?

Is the temperature sensor sending an accurate temperature to the ECU?

[LewisAV]

We unplug the Lambda sensor from the Green plug underneath. The sensor was good according to easymap but just incase we tried in and out.

The temperature sensor is next to double check tomorrow, but again it didnt show up as bad in easymap.

appriciate the response 

[aerobod - near CYYC]

Easimap may show the Lambda sensor is good, but being a narrow band sensor, it may still not be functioning correctly, transitioning between low and high values too slowly or having a bias due to contamination. With the sensor disconnected, Easimap should show open loop operation, if the car runs reasonably well in this state (not perfectly), then it is likely a bad sensor.

You should get an oscillation of the Lambda sensor output from rich to lean between about 3Hz and 0.5Hz at steady state closed loop operation (as indicated by Easimap).

The water temperature sensor should be within about 5C for a comparison of the Easimap temperature and the dash gauge (that uses a different sensor), with it climbing at idle to a point where the cooling fan activates (varies for different models, but is typically 90 to 105C)

[colindavies56]

TPS setting 4.2,who told you that. sure its 1.04,I'll have to check after work but I'm sure that's what mine is. 2010 150 roadsport. 

[Tom_Arundel]

What type of 1.6 Sigma....fixed cam.....125.....140.....150...etc?     How many miles?    How hard do you drive it?

Have you tried a small adjustment of the throttle stop screw (on the throttle body)? 

 Does it `Hunt` at idle?

If it is a 150, are the throttle bodies in sync.?

Check plug gaps are 0.9mm not 1.3mm

 Easy map should have transition 0-1 at idle and it is very hard to get right

[ChrisC]

I agree, "TPS sitting at 4.2" doesn't give enough information, is that voltage or throttle site.  The actual voltage will vary between Caterham model to model and MBE model to model, but in general the TPS throttle site should go from 0 at idle to 15 at full throttle in a smooth manor as the throttle is pressed.  Best to test this with the engine off ;-)

Some Sigma cars had a MAP sensor, with the hole open, pointing upwards near the ECU, so easy for water to ingress the sensor.  If the sensor isn't sensing atmospheric pressure you will get running problems.  I always recommend putting a small piece of hose on the sensor to create a u bend so the opening is pointing downwards,with a little length to prevent water strike.  It won't effect the sensor from detecting atmospheric pressure, but adds a little protection.