K series mixture problem

[Simon Dart]

Help! My factory built 1996 1.4SS just failed the MOT on emissions. I know I could find another garage I try and blag the kit car thing with, but something is obviously wrong, it wont cold idle cleanly. It passed no problems last year.

 

The tester ran the fast idle test twice, HC at 254 and 407ppm (should be less than 200), lambda at 0.865 ( 0.95-1.09) The CO around 5% ( should be less than 0.3% and 0.5% repectively)on fast idle and natural idle. The car has no cat. The Haynes manual was useless for any pointers. Any help would be much appreciated.

 

Simon

[Blatman]

Sounds like a knackered IACV, especially if it won't idle when cold. The answer is a new one, as they generally aren't repairable (at least, I've never heard of one being repaired....).

[Simon Dart]

The car does idle, it just dies a little when you pull away a . The IACV does its little whirr thing still when you turn off the ignition. I wondered if anything other than this or the ECU would have that effect?

[Blatman]

The IACV is in almost constant motion during idle, as it regulates how much air gets into the engine. Whirring on shutdown doesn't mean it's working properly.

I interpreted ".....it wont cold idle cleanly." as it seems to hunt for an idle speed, constantly going up and down a few hundred revs. If that's the case, I'd still strongly suspect the IACV, especially if it improves when warm. The usual thing to do with IACV's is to wait until you have a stable warm idle, then disconnect them, "freezing" them at a known good idle setting.

I doubt the ECU is giving idle or MOT failing emission problems, unless you've been playing with the map recently, or there is another cause. Perhaps a duff lambda sensor (do you have onequestion.gif) or maybe the crank sensor is dirty, or even a loose wire somewhere, which is affecting the readings to the ECU, which is then erroneously altering the fuelling. The only other possibility I can think of is that you've picked up some duff fuel from somewhere. Try re-filling with fuel from a "known" brand (ie not supermarket fuel), and if you normally use unleaded, try some super instead.

[Swiss_Tony]

I assume your car has the mems ecu (Standard Rover)

The idle etc can be reset by pumping the throttle a few times (I forget how many but 7 or 8 rings a bell) with the ignition on and engine off. Someone will be along to confirm this soon no doubt!

This probably wont affect the emissions at a fast idle.

Has the cat been removed?

If so it wont pass a cat test!

A temp sensor or lambda sensor can cause this amongst other things. It might be worth finding a local garage with the necessary gear to do a few checks. It should be the same as most Rovers to diagnose.

 

James

 

[Simon Dart]

Thanks guys,

 

I found a vacuum hose off the IACV, popped it back on and reset the ECU, seems to have done the trick. The re-test will be the acid test!

 

Simon

[fastjedi]

I had something similar on my 1996 1.6K about two years ago.....

Irratic and high idle speed (around 1400 rpm)

Wouldn't rev from idle cleanly unless under load

Unburnt fuel in the exhaust on overrun

I suspect it was an intermittant water temperature sensor connection .... Causing it at always think the water was cold and the "choke" to be on. Messing with the water temp sensor returned the idle to normal.

 

 

[Simon Dart]

Yup that was it. A fresh MOT for me yipee! Why does MOT time promote anxiety? I'm not a natural worrier but sitting in the waiting area waiting for the sword of Damacles is horrible.