Jumping Revs

[thom1983]

Evening all, noticed occasionally the old girl's revs seem to fluctuate by 200rpm, jumping up and down. Also seems to sit around 2000rpm when it's cold for first few mins...could it be o2 sensor?

Sent from my iPhone using Tapatalk

[sp3n5]

I`ve got the same issue.Does anyone have an idea , where could be the problem ?

[mikey-t]

The high revs on start up is due to the car trying to get to optimal running temp as quick as possible and is completely normal.

[+robster+]

petrol car idle revs up and down point to the common idle air control valve ( but could be a number of other things)

idle air control valves can become dirty with breathed engine oil vapour or can just fail

try removing for a clean. it costs you a can of brake cleaner or whatever you want to use.

[Cwp]

The same happens to mine. Cleaning the egr helps alot.

[mikey-t]

1 minute ago, +robster+ said:

petrol car idle revs up and down point to the common idle air control valve ( but could be a number of other things)

idle air control valves can become dirty with breathed engine oil vapour or can just fail

try removing for a clean. it costs you a can of brake cleaner or whatever you want to use.

Correct me if I'm wrong but the T25 doesn't have an IAC valve does it? When I took my throttle body off the only part to it was the motor and gearing to control the butterfly valve.

[+robster+]

thanks for input I'm just guessing on the hop here.

if so then that is later generation of same principle and acts as its own iacv and can still become gummed up or fail

this type ( that I work on) self calibrate every start up and do a full sweep and feedback the position range and if lazy or sticking then flag up mil

 

could be a vacuum leak drawing air ( as petrol engines rev governed by air input) as apposed to diesel governed by fuel input and matched by air)

[mikey-t]

2 minutes ago, +robster+ said:

then that is later generation of same principle and acts as its own iacv and can still become gummed up or fail

this type ( that I work on) self calibrate every start up and do a full sweep and feedback the position range and if lazy or sticking then flag up mil

Hmmmm very interesting. When I cleaned mine I noticed what felt like wear in the gears that translated slightly to the butterfly valve, is this normal?

[+robster+]

not wear in the gears with butterfly play no. it has to be rather precise holding idle rather than have any play.

 

but I'm just giving off the head answers I may be leading you wrongly. could also be maf but they usually just stutter and !Removed! up the first half of rev range

[+robster+]

nanny bot removed F&RT