98 Freelander Erratic Idle / HDC Light

I own a 98 1.8 K Series Freelander which until 2 weeks ago was running perfectly.

I noticed while driving that the engine RPM was sometimes sticking and not returning to IDLE on demand ( initially this resolved it self ).

Then 2 weeks ago it started to stick on every drive and on occasions it was extremely erratic with un requested increases in engine RPM. Which required turning the ignition off to prevent redlining.
We have changed the IAC ( Idle air control valve ) and the electronic part of the Throttle switch. Checked the vacuum hoses etc and have started to check for any chaffing on the electrical wire side of things. The diagnostic kit returns faults with a temp sensor and the throttle switch which when we check appear to work fine. ( However she appears to only have one fan in place, the nearside is missing ??? - previous owner maybe )

When I have done the manual reset with IGN pos 2 and 6 applications of the throttle the idle datum seems perfect ( 850 - 925 RPM ) however when you drive her it loses the plot and returns to the situation above. When you we remove the vacuum hose from throttle body to the IAC and cover it she returns to idle perfectly again??

I think it’s a ECU fault??

How interchangeable are ECU’s?

Any clues suggestions appreciated

Regards

B.

Hi,
The engine ECU will be a MEMS unit and they are coded with the alarm ecu as a pair.
On my K series Rover they can be swapped out as a pair and you need either recoded or different alarm plips to match the new alarm unit. You can have another engine ECU unit recoded as a new pair but obtaining a second hand ECU pair is cheaper.
BUT :scratching_chin::scratching_chin:
The problem you describe seems more like a sticking throttle body?
If the throttle body allows the butterfly to close properly the revs available via the IACV will not let them get anywhere near the red line. No air = low revs.
Give it a good clean and check for crud around the pivots, oil up the pivots and springs and check the slack in the throttle cable when at idle (it's important).
That was what caused mine to do what you describe - frightening tho' innit when it don't slow down!

Hi
I have a similar aged 1.8 with, what looked like, IACV, TPS or coolent sensor issues. It turned out to be the connector at the ECU. When I had the ignition on (engine off) and moved the loom I could hear the IACV operating. Turned out to be a loose connection on pin 6 of the front row of connection at the connector. This is the pink & black wire that feeds the sensors. I used a small screwdriver to slightly bend the connector in the ECU connector (be careful or you will be in trouble) and all Ok for several weeks now.

But also check the throttle body as suggested – I once had a tight cable that buggered up the tickover on another old Freelander I care for.

Re the fan – I think cars with no AC only had one fitted