Renault Scenic Megane 1.4 16v X reg (K4J) - Erratic idle, will stall every few minutesArchived Message
Posted by Dave Hill on July 31, 2006, 9:45 pm
The local Renault garage has looked at this one with no result.
The car has a very erratic idle & will stall every few minutes. If the revs are increased to 2,000 rpm then it will run albeit roughly. The instrument panel is busy with fuel, temp gauges & rev counter dropping as if the ignition is switched off. The engine management light is on & codes for ECU supply relay fault, O2 heater circuit (intermittent). The O2 heater circuit fault is coming & going as you study live data.
Battery voltage is good (engine off) at 12.6 volts & 11.5 under load. Charging nicely at 14.5 volts. I have checked earth & feed connections & have some strange results. Testing for a volt drop between the negative battery terminal & the engine block (clean alloy section) I am seeing a 3 volt drop at 2,000 rpm & when it comes close to idle I am seeing a volt drop from 2 volts up to 9 volts. As this is going on the gauges are all over the place & I can here a relay clicking in time with the fluctuation.
I have done a volt drop test from the + battery terminal to the starter terminal & found a similar volt drop of around 3 volts. I checked the battery for AC volts with the alternator disconnected & noted a 35 volt reading AC (not sure what to make of this).
All of the earth connections have been removed & cleaned & refitted (all the obvious ones anyway) I have had jump leads all over the vehicle to try to eliminate earth connection doubts.
There is a relay (relay B) in the fusebox under the bonnet near the battery that is clicking in time with the gauges & engine failing. I have backprobed (with a power probe) the terminals to this relay & the earth side of the trigger circuit is fluctuating between a feed & earth (also in time with the failing of the gauges & the engine). If I apply an earth to this terminal (via the power probe) then the engine idle stabilises although the gauges are still erratic. I have tried all of these tests with another multi meter in case the first is faulty.
I am pulling my hair out with this (for a bald guy, that’s a big deal).