420R won't idle when cold

[Solo]

Ok, so Saturday started car as normal - ran for a minute or so as normal then stalled. Sat in the car, started instantly and went out for a couple or hours or so with no issues.  Yesterday car started but wouldn't run without me applying some throttle.  10 miles later it still died at idle.  Once it was properly warm all seemed fine.  Tonight it's still won't idle without me applying some throttle.  I've checked all the connections to various sensors on the car are fully clicked home. It's full of fuel (I filled it after 10 miles last night).  Finally, it hasn't got wet for months.  It's 7 months old with 2,300 miles.

I shall try to speak with Caterham tomorrow but suspect they will want to see the car.  Any ideas about what I could check myself - it would be nice to avoid taking a day off work to do the 200 mile round trip to Sussex.

thanks

Steve

[aerobod - near CYYC]

Ideally checking the sensor values using an MBE cable with Easimap would show any implausible values. If you can't borrow or buy one, I would check the temperature sensor first. I believe the resistance should be about 2000 ohms when hot and 50000 ohms when cold, but basically it will change by at least an order of magnitude from hot to cold and become lower as the temperature rises. The air intake temperature sensor that is combined with the MAP (assuming plenum as opposed to roller barrels) should also vary in resistance as the temperature changes. The last resistance check is to see that the TPS resistance also varies smoothly with movement. I would also confirm the throttle idle stop screw hasn't loosened off.

[John Vine]

It would also be worth checking the loom wiring where it enters the TPS connector.  It's quite common for one (sometimes more) of these wires to weaken and eventually fracture. The result is very uneven and unpredictable running.  The cure is to fit the uprated race loom.  Of course, as your car is almost new, you may already have this (it comes with fat, flexible, silicone-sheathed wires).

JV

[ChrisC]

I have the MBE lead, and will save you a few miles.   I am also about at the weekend, to save time off work.

Chris.

[Solo]

Thanks for the suggestions guys.

Spoke with a very helpful chap at Caterham today (Mark) who suggested that my idle speed was too low.  It was around 900rpm, I've now set increased it to 1,200 which seems to have done the trick - idles fine when cold but obviously sounds a bit higher than I'm used to when warm.  They told me that the coolant sensor rarely gives trouble.  I'll keep an eye on this but hopefully it was a simple fix.

cheers

 

[aerobod - near CYYC]

1200RPM is quite high, I'm assuming you adjusted the idle stop screw to increase it?. It is worth checking with the MBE cable that your TPS site is still in the range of 0 to 0.4 while at idle, as you may experience idle hunting or lack of injector shut off at closed throttle when at higher revs if the TPS throttle site is 0.5 or above at idle, leading to drivability issues. You can make a very small adjustment in the TPS position by loosening the two screws (and potentially slotting the TPS screw holes slightly), to get it to the right throttle site.

My Duratec R400 idled at 950RPM on the standard Caterham 992 ECU, but I changed it to 1000RPM in the map when fitting an unlocked 9A4 ECU, it idles flawlessly.