Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Should I change ecu?

My 1994 plus 4 has a persistent fast idle issue. It idles at about 1050 rpm. I’ve changed the temperature sensor - no difference, checked all hoses etc. By way of this forum I know that the baseidle is set in the ecu but have no means of connecting to it. Is an ecu a straight swap! Should I take it to a dealer or just change the ecu? I should add that other than the idle the car runs and starts fine. What does the collective think?

Hi, I should check how the system is handling the idle: potentiometer on the throttle body ? Electronic air valve ?
And check first those components: position, move free or without play, use a multimeter to check that the potentiometer is well giving a value on all the range of movement, etc ...
Also check the cabling form the temp sensor to the ECU.
If nothing found then back to dealer to verify the idle value set in the ECU and if correct check the ECU
Unfortunately without ECU reader you cannot do much more

Check for air leaks the ECU on the T16 & I guess the M16 reads inlet manifold pressure after the throttle body. Mine had a pipe from the manifold to the ecu. Check it's condition.

If you do swap the ECU then you need to either repair it with the immobiliser of bypass it. I got an ECU where the immobilier connections were by passed

Changing the ECU will unlikely change anything, though who knows? Do you have a diagnostic reader?

The Rover T16 idle is controlled by the throttle plate and a stepper motor, working together. For example, if the throttle plate is dirty and cannot move freely it will not allow the stepper motor to reset itself. Stepper motor problems alone usually will cause wrong cold idle speeds aka too fast. So start by cleaning the throttle plate (aka the butterfly).

You can also buy a spray bottle of ether https://www.amazon.co.uk/Holts-Bradex-Easy-Start-300ml/dp/B000X2CR4W/ref=sr_1_1?crid=1WR3FCE1SIOVA&keywords=ether+start+spray&qid=1696862898&sprefix=ether+start+spray%2Caps%2C235&sr=8-1 Use it to spray around your engine hoses while idling. If your idle changes, you have fond your culprit. BTW, ether spray is a great brake and fueling part cleaner as it completely evaporates after a few moments.

L.

Ether ...... If you're spraying it about under the bonnet (rather than into the intake) ... the stuff is very inflammable ... which is why it's such a useful diagnostic tool 🙂 .... you can also get woozy on it (it was used as an anaesthetic back in the day after all) ... outside on the drive is a good precaution and the ventilation solves the major part of both the above observations.

K

It is used by most practiced mechanics and it is sold EVERYWHERE under different names. I have used it for 25 years, though I admit, before using it I had your fears. But there is no simpler way of diagnosing vacuum leaks and I do not want him to waste lots of money and time on a pressure testing for a diagnose technique he only needs once in a blue moon. He will be fine. And if he wants to test the ether, he can try a tiny bit first on his air intake.

But thank you for the tip on its human effects when breathed in. There are so many wonderful surprises that can be had when working with automobile fluids!! :cheers :

Gomog .... I'm never without a can in my workshop (OK, several cans 🙂) ..... as I said, a really useful diagnostic tool .... with a public forum you never know know how much 'bushcraft' other members have ... the OP may be well versed in ether sprays and I'm teaching my granny to suck eggs... but also might not be and spraying it onto a source of ignition would be a surprising learning experience out of the blue! 😄

K

Yes be careful with aerosols the propellent these days is normally butane so very flammable.

Thanks all. It really is an odd one everything is running fine other than a slightly fast tickover. No evidence to support this but it doesn’t seem like a stepper motor or throttle plate issue? Unplugging the temp sensor increases the revs at about 2000 rpm dropping immediately to 150 on reconnecting. I’ll try the east start recommendation as there’s some in the garage (thanks for the H&S advice!). It “feels” like an incorrect ECU setting. It’s feeling like a trip to the dealer hopefully before its SORN kicks in

Thanks again

Thank you.
Yes I am trying to address that. Uphill battle. But I love the cars.

L.