Mot Idle Speed

[daveyboyblack 1]

Evening all,

 

I failed the MOT test a while ago on "idle speed to high". I've since changed the icv/temp sender/afm and the car is running a whole lot better, and settles down to a nice steady idle once warm.

 

However... the rev counter won't go down to zero, and sits at 400rpm when the engine off. It'll now idle at an indicated 12-1300 so am I right in thinking that this is actually 8-900 or does the rev counter's initial position has no bearing on the reading once the engine is turning over?

 

Finally, how do they measure the idle speed itself during the test, i presumed it was just using the counter but my failure sheet had some very specific readings on it? It failed for being 1239rpm, but didn't state the actual range that they're looking to see?

 

Cheers

Dave

[welshpug 1,666]

I think often enough they will use a pickup that plugs in the fag lighter socket, if the signal is strong enough they will use that, I think some use inductive pickups directly on plug lead.

[Matt Holley 11]

Evening all,

 

I failed the MOT test a while ago on "idle speed to high". I've since changed the icv/temp sender/afm and the car is running a whole lot better, and settles down to a nice steady idle once warm.

 

However... the rev counter won't go down to zero, and sits at 400rpm when the engine off. It'll now idle at an indicated 12-1300 so am I right in thinking that this is actually 8-900 or does the rev counter's initial position has no bearing on the reading once the engine is turning over?

 

Finally, how do they measure the idle speed itself during the test, i presumed it was just using the counter but my failure sheet had some very specific readings on it? It failed for being 1239rpm, but didn't state the actual range that they're looking to see?

 

Cheers

Dave

 

Thay may have put a rpm pick up lead on your h.t lead, although there are several speeds they can take from this,its to do with the amount of cylinders you have but they normal flick through till they get a speed that matches your rev counter or sounds about right.

 

I say point out that your rev counter is clearly out and go from there, I can't remember off hand what speed thay want but I would think any thing fro 700rpm to 1100 would be acceptable.

[Miles 331 1 Cars]

You are allowed to turn the Idle up on older cars to pass the test, not sure what the top limit is thou

[welshpug 1,666]

I believe the computer will tell the operator based on the vehicles details (i.e he enters the reg and up comes the data to test to)