Its the pre cat one you need to change.
Long Term Idle Problem Help
Posted 14 November 2014 - 6:37 PM
Hi there again,
Thought id update my situation on whats been going on for anyone that ever comes across a problem like this.
Well its been around a month since my last problem.
I changed the pre lambda sensor and lucky it came off so easy. Still poor idle.
The next week I took out the whole inlet manifold and changed both gaskets with the upgraded green ones. Still poor idle.
I then took the car out and revved it just under 8k as the car seems to rev high and the idle problem cleared itself. Ive ben driving around for a month with hardly any problems than the odd bit of rough idle on the odd occasion.
Took my girlfriend out for a meal pulled into a carpark and it started cutting out and the rev needle was up and down between cutting out and 1200k. Went and had food, warmed the car up with a slow careful drive to my nearest bit of straight road. Put it in 2nd and revved the car to 7k let off and went back to perfect again. Was ok for 2 days and now its rough again.
Im not going to try and correct it though as i think whatever intermittent problem i have seems to be turning into a full time problem.
I just don't know what the next thing to do is? Im thinking Throttle position sensor? Or am i barking up the wrong tree?
Posted 14 November 2014 - 9:49 PM
Hey Jamie, FWIW here's my current theory about this;
Sometimes when I start the car the alarm red warning light on the stack flashes up. Normally I stop the engine, press the remote to cancel the alarm and restart.
Now what I think might be happening is the voltage to the ECU is dipping too much on starting, probably because the rear chassis earth point is a bit corroded and is going high resistance. That rear chassis earth point brings together the battery earth lead, the wire going off to the starter solenoid, and the ECU earth return.
My theory is that the ECU is resetting each time the battery volts dip too much, meaning it loses the idle settings and has to re-learn.
I had a look with a mirror last weekend and it did look a bit manky.
Anyway, I'm going to tackle the rear chassis earth point this weekend, and see if it makes a difference.
I'll let you know how it goes!
Posted 15 November 2014 - 4:58 PM
I've found on-line that 9-11V is normal for the battery voltage while cranking, so it looks like my battery is about done.
(That trace is actually on the battery terminals).
Edited by Wildspark, 15 November 2014 - 5:01 PM.
Posted 17 November 2014 - 10:06 PM
Oh ok, Cheers for the info, my battery is new, i hope it all clears up for you, gonna spend a night having a last look before its booked in to Lotus i think
Posted 27 March 2015 - 7:05 PM
An update on my idle problem. I finally got round to changing the pre-cat lambda sensor, and the problem seems to be solved. The idle was dropping from 850 rpm to about 500 rpm every 10 seconds or so, only when hot.
It now sits almost perfect at 850 rpm. When I first ran the car after changing the sensor it was hunting just slightly, but another run I assume has allowed the ECU to learn the idle and it's now sweet.
I do recommend the lambda socket wrench here;
It's a bit expensive but absolutely perfect for the job. Really solid build quality and fits the space perfectly.