Strange fast idle

[cameron]

Went to do the emmissions test the other day, so gave her a good old warming up, at least a half hour motorway drive.

Got back to the garage and went straight on the tester, put all the details of my car in, all the while the cars still running, the computer asks me to raise the revs to between 2500 - and 3k which i do but then the revs start dropping back off by about 250 and then coming back up by them selves :confused:

The emissions are going to pass until this starts to happen and then when its coming back up the revs by itself its going over and failing :cry:

I had emmissions troubles last year and i could really do without it this year, on an up beat note the lambda reading is spot on so my 2nd hand cat off Gary ( siamblue ) is still working brill :B_thumb:

Any ideas as to what can be happening with the revs ?

Cheers guys :D

[Jamest5r]

That rpm is when your turbo starts spooling up i had similar probs in dec with my auto they could'nt hold the revs at 3000 but they are v understanding and sorted it :wink: i changed the maf and and it stopped later on

[cameron]

I thought of that Jim so dropped it to 2k then just under maybe about 1750rpm but it was still doing it :doh:

It doesnt do it at natural idle and it cant be my foot as im using a thing that i can only describe as the same sort of mechanism that you have in a silicone gun thingy ?

You know the thing, it hooks under the bottom of the steering wheel and onto the accelerator pedal, pull the trigger to set it and it stays there until you release it, so theres no change in the accelerator position.

[Volvostorm]

Alot of cars seem to do this, most testers find ways to get around it, and most emmission testers wait a few seconds if the revs creep outside the limits, with a bit of juggle of the throttle you can get them through ;)

Also, have a check for air leaks

[cameron]

First thing i checked Paul :B_thumb: Great minds think a like.

Strange thing is though if i start the car from cold and hold it at 2k on my foot it stays there for a good 30 seconds then it starts its up and down carry on :cry:

I dont think the lambda would go through from cold as it was pretty close whilst it was boiling hot.

[nobananas]

We often get this with vehicles whilst doing emissions testing at work. Sometimes simply keying the vehicle off then restarting can cure it, sometimes loading the alternator up by turning on lights and rear screen demister can also settle it down. I'm assuming you don't have any air leaks ?. Also sorry to be a nit picker but the condition of the cat doesn't usually affect the Lambda readings, you could remove the cat altogether and the Lambda readings would still pass but the CO readings would fail,.....can you tell I do this everyday and am thoroughly fed up with it !

[Volvostorm]

Lambda isn't used from cold, it uses the ecu map, thats why you have to warm the engine up before testing