Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Idle hunting on restart – 1990 Plus 4, Rover M16i

Car: 1990 Morgan Plus 4, Rover M16i engine, 1994cc, DOHC 16V, indirect injection, Lucas 14 CU electronics.

Situation 1 – Cold start, then driving outside: the engine runs smoothly and stable.

Situation 2 – Cold start, drive outside briefly, switch off the ignition, close my garage door (only a minute or two), then restart the engine (still essentially cold). At this point the idle speed rises to around 1700 rpm, then drops to around 1000 rpm, then back up to 1700, then down to 1000 again — repeating this cycle back and forth.

Has anyone experienced this same pattern, and if so, what turned out to be the cause?

Check al the air hoses. There is a vacuum line sizzed hose from the inlet to the ECU (at least on a T16) that easily perishes.
It could be the start of ECU failure , mine would idle fine, not at all or at 5,000 rpm.

I have had this sort of issue for 14 years with my 93 T16. the high tick over can be cured by re-starting or switching off the red battery isolator.
Unable to buy the correct ECU I am resigned to living with it. If you can buy the correct ECU it would be worth doing that to eliminate that, if its not that, at least you have a rare spare.

Thanks for replay! If you have problems with your ECU. The most sensitive components in an ECU are the capacitors. An old-school radio and TV technician can measure and replace them. This was actually a line of thought for my problem as well. But I wanted to inquire whether there are any known issues with the sensors or other mechanical malfunctions.

Yes MogPat, you are of course correct, however I am reluctant to entrust my ECU to a repairer as I do not have a spare. It works ok when running so until I can find/ buy a spare to send for repair I will live with the intermittent tick over.
What I am suggesting is due to the age of the ECU buy a spare, you may have more luck than me sourcing one.

My ECU is Motorola MKC100034 E if anyone out there has one even if it needs repair.
It would appear it comes from a Rover 820 around 92/3 most of which were exported to Spain it seems.

Hi John V6

I know absolutely nothing about this Rover engine or its ECU but I am intrigued to know. Do I understand correctly that this ECU has a physical hose connection presumably with some type of pressure sensor built inside ?



Tony