Idle Speed MOT Failure

Post by **robster01** » Mon Apr 04, 2022 3:08 pm

Hi all,

Probe's gone in for its MOT today and failed with the only fault being a high normal idle speed. Called the garage and they've said its not dropping back to 550-750 rpm following the fast idle, so the machine won't let them continue with the second fast idle test. Tested and recreated it myself, the normal idle level is fine around 500rpm but bringing it up to 3000 rpm then dropping it back down leaves it idling at what they tested at 824 rpm. Anything I can do outside of flushing the coolant system through?

Also saw on a previous MOT that the range it needed to hit was much wider at 400-1500rpm, do different testers have different machines?

Thanks for your help,
Rob

Post by **Micron** » Mon Apr 04, 2022 3:23 pm

how's the water level, is it a 24v? if it is check the level on the cap on the left. It should be full.

Post by **robster01** » Mon Apr 04, 2022 3:28 pm

Micron wrote: ↑
Mon Apr 04, 2022 3:23 pm
how's the water level, is it a 24v? if it is check the level on the cap on the left. It should be full.

Topped it up, will give it a run tonight to see if that does it. The whole system has quite a lot of rusty sediment in so definitely going to flush it out too if just the level doesn't fix it

Post by **Micron** » Mon Apr 04, 2022 3:30 pm

robster01 wrote: ↑
Mon Apr 04, 2022 3:28 pm

Micron wrote: ↑
Mon Apr 04, 2022 3:23 pm
how's the water level, is it a 24v? if it is check the level on the cap on the left. It should be full.
Topped it up, will give it a run tonight to see if that does it. The whole system has quite a lot of rusty sediment in so definitely going to flush it out too if just the level doesn't fix it

Was it low, did you have to put much in it and if you did, did you bleed the air out afterwards?

Post by **robster01** » Mon Apr 04, 2022 3:50 pm

Micron wrote: ↑
Mon Apr 04, 2022 3:30 pm

robster01 wrote: ↑
Mon Apr 04, 2022 3:28 pm

Micron wrote: ↑
Mon Apr 04, 2022 3:23 pm
how's the water level, is it a 24v? if it is check the level on the cap on the left. It should be full.
Topped it up, will give it a run tonight to see if that does it. The whole system has quite a lot of rusty sediment in so definitely going to flush it out too if just the level doesn't fix it
Was it low, did you have to put much in it and if you did, did you bleed the air out afterwards?

Yep followed the guide in another thread. Didn't have to put much in but know they can be tempermental when not full. It's Dorset Dave's old blue 24v and got through the rest of the MOT with a completely clean bill of health. Got 10 days to get this sorted for the retest

Post by **Micron** » Mon Apr 04, 2022 3:51 pm

give it a try when you can and see how you get on? A flush may not be a bad idea?

Post by **cpt black** » Mon Apr 04, 2022 4:20 pm

Tick over should be appx 700/750 (+ - )50 rpm check your base idle and check throttle cable
returns back to its stop

Post by **robster01** » Mon Apr 04, 2022 4:55 pm

Both seem to be fine, idle on start up (warm engine) is around 650-700, then when it comes back down after a fast idle it sits at around 850. I'll take some videos tonight and upload. Found a garage that will let me do a free emissions test before I go for the MOT retest so that's a good option once I get it down

Post by **robster01** » Mon Apr 04, 2022 6:58 pm

The car is failing the initial Basic Emissions Test as the CO level at fast idle is over 0.2%, so it moves onto the extended emissions test, which requires the levels detailed in the annex in the MOT test guidelines. The idle speed they need it to be for the test is a bit lower than what's recommended on the owners forum and it's also going to be nigh on impossible to set the idle between 600 and 700 rpm given the dial we have isn't super accurate. I think I'm therefore better off trying to get the CO emissions down for now.

Post by **Micron** » Mon Apr 04, 2022 10:06 pm

Do you have a copy of the actual emissions test that you can post?

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