IDLE SPEED GOES UP AND DOWN

[marco2002]

Hi everyone,

I have a strange problem the 406 which i suspect is electrical. I fitted a new radiator and bottom hose on monday . The wiring loom that runs from the ecu and round the front of the engine (sits in a plastic conduit) was sticking out a bit so i pushed it back into the slot with one finger and then the engine idle speed went erratic sounded almost like it was about to stall. Then it went back to normal. I thought it was a bit strange so i touched the same spot on the loom again gently and it did it again. Now i'm thinking theres a loose connection in the loom around that spot. The wires are all taped up but it doesn't look like the original loom. I've had it 6 yrs now and no ones fiddled with the wiring. It was like that when i bought it.

Anyway to cut a long story short when i went out this morning it was cold but it started okay the idle speed was going up and down a bit and it sounded like it was going to stall. When i got down the road and the engine had warmed up(about 70 degrees c) doing 40mph to town the idle speed was fine again. I am wondering if this problem is related to the loom or is it something else? Before i start to unwind the electrical tape on the wiring loom and have a look tommorow i wondered if anyone had any ideas. It has just had the engine oil/filter changed a week ago, air filter and fuel filters changed a couple of months ago. I was thinking about having a look at the wiring first then if i can't find any loose connections i'll take it from there. Prior to monday the car was fine. The eml came on not long after i touched the wiring loom at the spot i found then it mysterously went out the next day after about 3-4 cycles of running the car. Any help appreciated. Thanks

[Doggy]

It sounds like you have a bad connection to one of the sensors - possibly coolant temp. from your description. It would help if you advised the age of yor car - early diesels had 3 coolant temp. sensors, (for gauge, ecu & fan control), whereas later fully-multiplexed cars only have one.

Sticking with the water temp. for a mo, are you certain you got all the air out of the system after the radiator change - these cars are notorioulsy tricky in this respect.

A diagnostic session with a PP2000 system would reveal a logged intermittent fault for whatever lit the EML, reading it with most other stuff will just give you generic fault code(s).

[marco2002]

Hi
My 406 is 110 on w plate (2000) its an early one. I'm 99% sure i got all the air out used the bleed valves and i used a header tank made out of an old coolant bottle with some tape round the bottle to make a good seal with the cooant tank. I'm going to check the wiring on the loom at the spot where i pushed it i've bought a roll of black electrical tape have acouple of hours off tommorow .

Like you said i reckon the loose connection is in the loom as when you touch it with your finger the revs shouldn't go up and down like that. I might give the coolant sensor a clean with some contact cleaner and re-connect can't do any harm. Once the car is up to temperature i usually feel the coolant hoses top and bottom hoses are the same temperature. The car heater at 30 degrees is nice and hot. I'm satisfied theres no air in the system. Temperature guage is sitting at just under 90 degrees same as it was before. On the dual carriageway at 50-60mph its running at about 80 degrees so its a bit cooler with the new radiator. Thanks For the info about the sensors and i'll update when i've had a look at the wires. Cheers

[marco2002]

Hi
After a lot of mucking about took the tape off the wiring loom and it took about 30mins to figure it out there is a big yellow connector that sits on the front of the engine on a plastic clip. One of the wires had snapped just held on by a strand. Used a crimp connector to connect the 2 wires together and all seems well. The EML came on again i reckon it will go out again at some point tonight. I'm also thinking that in the last 6 months its come on a couple of times and gone out after a couple of cycles so maybe the wire snapping gradually over time was causing an intermittant fault. I am interested to know what the 3 wires on that yellow connector do? Took it for a test run to the garage to get fuel and it feels a lot better. Off to work tonight so should be able to fully evaluate it. I've noticed my fuel consumption has been lower just lately only getting about 44mpg instead of 47mpg. Maybe also has something to do with the split wire. Thanks for your help Dogslife. Have to think about getting pp2000. The mechanic that did the cambelt on my car said you have to watch some of the pp2000/lexia 3 clones as they can spike the ecu?

[Doggy]

Have to think about getting pp2000. The mechanic that did the cambelt on my car said you have to watch some of the pp2000/lexia 3 clones as they can spike the ecu?

News to me - never had a problem with mine, or heard of anyone else experiencing this. (I've heard of the odd one that doesn't seem to want to talk to everything, but that's it).