Idle Hunting

[meeko]

My 97 Chim 400 has always used to tickover between 900-1000rpm. It was pretty smooth too. It's just started to "hunt" where the revs drop down to almost stalling and then it springs back into life. This happens whenever it's left to idle for a few seconds. It seems to drive the same though.

Not sure if it's relevant, but we had the heaviest storm I've ever driven in the other day and it was the next morning that I noticed the problem. The car seems to be bone dry inside though.

Help!!

[Big Al.]

I know it's a classic response, you have obviously cleaned the Stepper?

Give the engine bay a good spray around with WD40 I found it helped immensely.

[Paul (93 Chim)]

Have you had a flat battery or been disconnected? as this would set the ECU to the default values and would take a while to settle down.
If not Steppa Motor may need cleaning as previous thread.

Regards,

Paul.

[raw-sewedge]

Inclided to agree with Al on this one. It would be my first port of call.

[Mad Mitch]

I know this should be obvious but for those to which it is not, only apply wd40 when engine is cold.!!! Burns very nicely on hot manifolds.

[JonathanT]

Mine was eventually traced to corroded contacts to the ECU.

[meeko]

Thanks for the tips guys. It was only serviced about 2000 miles ago and they did clean the stepper. Would it soot up that quickly? Also this happened straight after heavy rain. It now idles perfectly sometimes and others it hunts so badly it stalls.

I'll clean the stepper and check the ECU contacts. BTW the battery is good and I have't disconnected the ECU. Will let you know who it goes...

[meeko]

Ok, touch wood, have sorted the Chim. I filled it with a whole tank of Esso 97 (which I always have used) and within a mile of leaving the station it seemed to behave itself a bit better. Still running a little rough, but at least it didn't stall.

I then cleaned the stepper (which was pretty clean anyway), cleaned the butterfly (which was almost spotless) and checked the HT fittings. One of the leads wasn't completely clipped on a plug. Also sprayed a nice amount of WD40 on leads etc.

It started beautifully this morning. Within 30 seconds of tickover from cold I pulled away and it didn't miss a beat. Wasn't lumpy like it was even before this fault developed! Very pleased.

Only only get about 180miles absolute maximum on 48 litres of fuel - which is 17mpg. Does that sound about right for a 4ltr Chim? Even when I drive it carefully and never floor it I don't get more then 17mpg. My driving profile is 60 % A road and no stop-starting with 40% around town.

Cheers,

[meeko]

I must have spoken too soon. I managed to cover about 90 miles since fiddling with the engine and it behaved perfectly. Got in to work this morning and it was ticking over at about 200rpm (quite smoothly though) and then hunting up to 1500rpm etc again.

I wonder whether thd stepper is faulty and the cleaning of it was enough to get the mechanism working temporarily. Can it be tested by removing the connector plug when tickover is high - i.e. will this keep valve open?

[lig]

Hi Meeko,

I have had this problem for a while now on my Griff. It seemed that I could reset the ECU and it would be fine for about 3 journeys and then start to act up.

I then checked the throttle pot and the voltage was out, it read 0.55 volts when it should have been 0.33 volts. I corrected this and this helped but the problem then came back. I then checked the AFM setting and this was out at 0.5v when it should be 1.5v.

It has been fine since (about a month and lots of journeys). But I am not holding my breath!!

So....It would be worth checking these values before shelling out on a new stepper or anything.

drop me a mail if you want more info on setting the AFM and TP.

Regards,
Lig.


>> Edited by lig on Tuesday 25th October 10:48

[meeko]

Thanks for the tips. I'll fish out my multi-meter and check these components.

Cheers,

Steve

[lig]

Hi Steve,

Keep me posted on how you get on. And if you find the ultimate fix!!!

Lig.