DaveK

Since having my car MOT'd last week, the idle has been a little uneven - mostly stable, but would sometimes increase up to about 1200rpm. Although my oil level is not high, I assumed some oil had got in the ISV since it was a warm sunny day and they left the car idling for about 40 minutes.....

On the way back from a 200 mile round trip today, I slowed for a junction and as I put my foot on the accelerator had no power. A second later it recovered.

Further on, slowed for a roundabout, and again - as I put my foot on the accelerator I'd lost all power. It would run at idle, but had no power if I put my foot down.

I limped to a layby, where the car idled a little unevenly - revs climbed up to about 2k rpm a couple of times. Switched the engine off, and had a prod around the engine bay - no obvious problems. But it did smell incredibly rich.

Tried to restart - didn't want to know. So although I thought it would make no difference, I swapped the (surprisingly hot) DME relay.

Took a few turns of the (now flooded) engine with foot on the accelerator - and then started up fine. Idled smoothly, and ran perfectly for the next 80 miles home.

I can't really see how a DME relay failure would only show when I was slowing (foot off the accelerator) and then tried to accelerate again, and I don't see how it would allow my car to idle (albeit not perfectly) but wouldn't let me pull away.

But the fact remains - swapping it did seem to cure it for today. But I'm dubious - maybe the DME reset helped more than the new relay?

I guess I can stick the other one back in and see what happens, but I wondered whether this sounded like a DME relay failure to anybody? In 6.5 years I've not actually had one.

Indycam

"(surprisingly hot) DME relay"
Relays should not get hot .
The contacts should be clean and big enough to flow the needed current without getting hot .
I think that the contacts were flowing current via some messed up contacts that were arcing and getting toasted and arcing and getting more toasted over and over .
I bet if you pull the cover off and look inside you will see old black crap contacts and bad solder joints .

Danz C4

The symptoms are very similar my situation just a week ago. I was driving in slow traffic, about 30 mph, about 2,200 rpm. Basically idling along with very little throttle. As the traffic began to clear, I pressed the accelerator, and no response. After a second or two it caught, then after a few seconds, no response. This time, no throttle for about 10 seconds as I drifted to the side of the road. Before I came to a complete stop, throttle came back. Same as DaveK, the engine did not die, just wouldn't rev above idle. Acted like the throttle cable was disconnected. Drove the car another 100 miles that day and no more problem. No problem since then. I didn't think of the DME and have not checked that.

My idle is stable, and ISV was recently checked to be clean.

Can anyone say if this could actually be related to the DME? Seems if the DME was bad, it would just shut off fuel and stall.

Danz C4

DaveK

That was one of the reasons I doubted mine - the smell suggested that burning the fuel was the issue, not supplying it.

But, the relay definitely was hot - to the point you wouldn't want to hold it for too long. So it does seem like a probable culprit.

Edit : Just opened the relay up - and inside it looks pretty good. As good as new in fact.
I'll have to see whether the car misbehaves again in future.

CraigyB

FWIW, in my experience, hot relays are normal when they are in the energised state. That is you have electricity passing through a coil (which gives off heat) in order to keep a contact closed. This is different the heat generated by a juddering relay, which only happens briefly, as failure of the relay is typically very quick once the contacts go bad.