2000rpm idle 420s

[Ant2]

I have a 2020 420S SV with roller barrels, so ecu was remapped a few years ago.

I've only had it about 6 weeks.

Over the last few days I've noticed the car can idle around 2000rpm, is this normal?

 

From cold it always idles around 850-1000rpm after first starting.

After driving though the car can idle up to 2000rpm, this catches me out as sometimes I end up putting too or little gas or too much or little clutch. 

Regardless if it's up to temperature or not.

It is not consistent which is quite odd,i.e sometimes it idles nicely at 1k rpm.

I am not sure if it has always done this and I never noticed as was getting used to the car or it has just started.

Thanks 

[John Vine]

No, it's not normal.   My R400D (with RBs) idles at around 900-950, hot or cold.

First, check that the throttle cable and pedal operate freely and that the barrels all close smoothly in unison.

When you say "remapped", was this the generic RB map from CC or following a rolling-road session with a specialist?

ETA:  Be aware that a "closed" RB will still show a 6mm gap (when viewed down the trumpet.)

JV

 

Edited May 7 by John Vine

[simon_h]

It might be a bit of grime around the barrels causing it to stick hot, could be a slightly frayed throttle cable.

I would disconnect the cable and see if the barrels can be opened and return smoothly by hand. Also see if the cable runs in and out cleanly 

[Jonathan Kay]

1 hour ago, simon_h said:

It might be a bit of grime around the barrels causing it to stick hot, could be a slightly frayed throttle cable.

I would disconnect the cable and see if the barrels can be opened and return smoothly by hand. Also see if the cable runs in and out cleanly 

Yes, check for stickiness all the way from the pedal to the throttle. With it all connected, and then each component with it all disconnected.

And the next time that it happens play with each bit to see if the speed drops back.

Jonathan

[Ant2]

Thanks all. Sounds like I should be taking it back to the garage for them to look at this, shame it's a 4 hour round trip. 

It definitely wasn't idling as high as 2k before.

 

I've uploaded a video with an example, idling moving around 1500-1600, blip of throttle a few times then causes the idle to move around

 

 

[Ant2]

Throttle cable and pedal feels smooth, no sticking. 

• I removed the tb cover and tested pushing the throttle and they all appear to be opening and closing unformly, with no stickiness

 

[Nigel B]

They look like butterfly throttles to me. 

As other posters have said, it could well be a sticky throttle cable. When I had a VX Seven on carbs the cable would often get gunked up. A motorcycle ‘cable oiler’ was a useful tool for directing lubricant down the outer cable, it worked wonders.

[John Vine]

22 minutes ago, Nigel B said:

They look like butterfly throttles to me.

Indeed. 

Rollerbarrels look like this:

They open and close rather like a gas tap.

JV

[aerobod - near CYYC]

1 hour ago, Ant2 said:

Throttle cable and pedal feels smooth, no sticking. 

• I removed the tb cover and tested pushing the throttle and they all appear to be opening and closing unformly, with no stickiness

 

With those throttle butterflies, 0.05mm of movement is enough to send the idle up or down by hundreds of RPM. They may be held open by tension in the throttle cable, ensure the throttle quadrant is always touching the throttle stop at idle with the engine cold or hot. Other issues are that the throttle stop may also have moved or the balance between each body may be off.

If you have Easimap, check the TPS voltage at the idle position, if not put a volt meter on the TPS and check the voltage at idle. If it is a standard Jenvey system with Colvern TPS, it should be about 0.30V (or 4.70V if reverse wired). I would then put some slack in the throttle cable by marking the existing position of the cable tension adjuster at the throttle body end, then slacken it off a few turns. Next is to check the existing throttle stop position, mark it, then check when the stop is slackened off that the butterflies completely close and the TPS voltage drops about 0.05V, then return the stop to the initial position.

Each throttle body should also be checked with a synchrometer for air flow at idle to ensure they are as close as possible in flow rates, if not close down all the bleed screws, pick the throttle body with the highest flow rate, balance it's twin in the same body with the bleed screw, then adjust the linkage between each throttle body pair to get the same flow rate for each pair. This is an iterative process.

This document from SBD gives a lot of good info for Jenvey throttle body setup: https://www.sbdmotorsport.co.uk/app/uploads/2020/11/2L_Duratec_TP-DURA-2-0L-K3_Taper_Throttle_Kit_Instructions.pdf

Be aware that if you move the TPS, it will affect your mapping overall, ensure you know what it's starting position is if you do move it. It is worth checking it's full range with Easimap or a voltmeter, wired in the increasing voltage with throttle manner, it should go from 0.25V with butterflies completely closed to close to 4.50V completely open (move the quadrant by hand to the full open position, as the throttle pedal may not be opening it fully)

[Ant2]

Thanks all.

The garage seems to think it's just the lambda sensor at fault and suggest they replace it.

I am starting to think it's more the throttle is sticking as I noticed a few times now where the throttle did not move like I expected and I had to suddenly push the throttle really hard, while  puling l off,  to stop it from stalling. (It's hard to tell for me as I have only just got the car) - I am surprised it can be sticking after only 5000 miles from new , but either way.

 

Oiling this cable,  Can I just shoot some 3 in 1 multi purpose oil in a straw down the hole the cable is on? I guess this will be the simplest way to see if this is the issue or not

 

The only thing is I see this heat proof cover is very close to the throttle (see pic 172917), so I have moved this down further the other way in case it nips it on occassion.

 

As the cable goes in to the pedal box, is this meant to be secured in some way so that the black plastic is flush ? The connector seems to free floating. When the throttle is pushed it just gets pulled in

Edited May 7 by Ant2

[aerobod - near CYYC]

The black plastic piece does free-float, shouldn't be a problem if the outer cable is not kinked. The air filter bottom "hooks" that go into the backing plate look a bit close to the Jenvey return spring and guide rod, I would confirm there is no touching there.

I would also check the cable on the exhaust side of the engine to see that it runs far enough away from the exhaust that it is not affected by the heat or degraded from it.

Edited May 7 by aerobod - near CYYC

[Ant2]

Definitely not touching.

I am now pretty convinced this is not the cable. Took it out again and idles perfect when cold, every time.

Once engine starts getting hot it will then start high idling (on occasion).

I can also have it low idling fine, left stationery and then start high idling and go back forth. It doesn't appear to be mechanical at all. i had the bonnet off to see if i can see the throttle cable moving at all and i can't, if it was I'd expect to see it getting unstuck and staying low.

I presume it could well be this lambda sensor as it appears to be coming from the ecu. Is there any way I can validate this without buying a 150quid data cable and software?

I.e could i just unplug the connector either when it's actively idling high and then see if it stops this erratic idle. Or just unplug it before starting?

I understand it will run quite rich, but would it be a good test to see if the idle issue is related to a dodgy lambda before driving 4 hours to have it tested and replaced?

[aerobod - near CYYC]

21 minutes ago, Ant2 said:

Definitely not touching.

I am now pretty convinced this is not the cable. Took it out again and idles perfect when cold, every time.

Once engine starts getting hot it will then start high idling (on occasion).

I can also have it low idling fine, left stationery and then start high idling and go back forth. It doesn't appear to be mechanical at all. i had the bonnet off to see if i can see the throttle cable moving at all and i can't, if it was I'd expect to see it getting unstuck and staying low.

I presume it could well be this lambda sensor as it appears to be coming from the ecu. Is there any way I can validate this without buying a 150quid data cable and software?

I.e could i just unplug the connector either when it's actively idling high and then see if it stops this erratic idle. Or just unplug it before starting?

I understand it will run quite rich, but would it be a good test to see if the idle issue is related to a dodgy lambda before driving 4 hours to have it tested and replaced?

You can unplug the Lambda sensor and it will stay in open loop control. Also, when the engine is above 60C and the car is re-started, the Lambda closed loop control will typically not start for 60 seconds (can be other settings such as 30s, 120s, etc, depends on MBE setting tuner has used). If either of these conditions cause a change in engine behaviour and the engine behaves better when the sensor is not causing closed loop control, then the sensor is probably bad.

[Ant2]

Thanks for the tips. Couldn't manages to get the plug off as it's all clipped in and it's booked in for monday.

I confirmed that the issue never happens on cold when in closed loop control, then when i cut the engine and restart it also goes away for a minute, which is inline with a bad lambda.

I manged to find my bluetooth odb connector and I see p0422 error - main catalyst efficiency below threshold - bank 1.

Took it for another drive and sometimes it also idles far too low and it stalled, which is even worse and put me off driving it till fixed. I read up on the voltage outputs and apparently they are meant to bounce between v0-v1 constantly.

Well mine reads above 1v statically and that indicates rich, presumably the engine then puts in less fuel, which is why I am sometimes getting hesitation pulling off.

It's booked in the garage for monday, will report back how it goes and check the readings after as may be useful to others or if this happens again

[KnifeySpoony]

My vote is for TPS.

[Doc007]

I may be wrong but I’m not sure OBDII readers can glean a whole lot of information from Caterham’s. Where do you live? Gotta be someone nearby with a cable. I’m in Surbiton in Surrey if that helps. But I’m not terribly proficient at interpreting it!

 

[Ant2]

All fixed.

Was a faulty TPS sensor, apparently the Jenvey one's are not well made. It was reporting completely incorrect readings, which explained all my weird symptoms.

I now have an aftermarket one fitted that are apparently more reliable.

My lambda has also been replaced.

Edited May 13 by Ant2

[Jonathan Kay]

Well done.

Thanks for adding the solution.

Jonathan

[StevehS3]

I don’t know if this applies to the Duratec but with the Sigma TPS it is important not to over-tighten the two fixing screws. They require the minimum of tightness. Just enough to keep it in place - nothing more. 

[Andy135]

Glad you got a solution, but as other have said, you appear to have butterfly TB's not roller barrels. Was it sold to you as having RB's? Assuming you haven't retro-fitted butterfly TB's it might be worth a phone call to whoever you bought it from if so.