slightly higher than normal idle

[griston64]

Noticed this morning that my idle seems slightly higher than normal. Its closer t 900 than 750

When stopping at a junction it goes a little higher then settles to 900 ish

Any initial idea what could cause this ? Only started this morning

[griston64]

Just to clarify car is 1996 940 Engine is B230FK

[Laird Scooby]

Was the air-con running Mark? Also is it a while since you've used it? Got a couple of ideas but not sure which is the more likely without the answers to those two questions.

[griston64]

Originally Posted by Laird Scooby

Was the air-con running Mark? Also is it a while since you've used it? Got a couple of ideas but not sure which is the more likely without the answers to those two questions.

Hi Dave

Car has been used daily and doesn't have air-con

[Rversteeg]

Does it persist after a restart?
For correct idle speed setting the engine has to be warm and being allowed to run a few seconds with closed throttle and stationary car. Sometimes, if the ECU did not have a chance to set idle speed for a long time, my idle speed remains too high as well. If that happens, I can only force it to re-adjust by slightly choking the engine with the clutch to 500 rpm or so.

[griston64]

Originally Posted by Rversteeg

Does it persist after a restart?
For correct idle speed setting the engine has to be warm and being allowed to run a few seconds with closed throttle and stationary car. Sometimes, if the ECU did not have a chance to set idle speed for a long time, my idle speed remains too high as well. If that happens, I can only force it to re-adjust by slightly choking the engine with the clutch to 500 rpm or so.

Not restarted yet so will find out when I head home this afternoon

[Ian21401]

My engine is a B200F. No AC. The indicated idle is usually about 600rpm but when I checked with a handheld tach. whilst doing something else it indicated 750rpm. I checked TPS etc. and all was correct so I did not investigate further. Starting quite some time ago the car’s tach. would occasionally indicate about 900rpm at idle but after a few minutes of normal motoring would return to the normal 600rpm indication. I have attributed this to a minor intermittent fault in the tach. or it’s signal and as there does not appear to be any other problems I have not investigated any further.

[Rversteeg]

Same here, the RPM indicator sometimes jumps a few hunderd rpm down to indicate a lower speed than the engine is actually running. It is just the tacho and not the ignition, as you do not notice any difference in the actual engine speed. It has been doing this every now and then for many years now, so I am not too bothered about it.

[360beast]

Might be idle control valve needs a clean Mark, I really should do the one on my 940 while it is off the road. In mine if I set of after starting very quickly when coming to a standstill in drive the revs would be that high the car was being pulled along by the engine. If I dropped it in to N it would idle about 1200-1500rpm until I came to a complete standstill for about 5 seconds, then it would slowly come down. However if I start the car up and let it idle for about a minute before setting off it very rarely happens.

[griston64]

Originally Posted by 360beast

Might be idle control valve needs a clean Mark, I really should do the one on my 940 while it is off the road. In mine if I set of after starting very quickly when coming to a standstill in drive the revs would be that high the car was being pulled along by the engine. If I dropped it in to N it would idle about 1200-1500rpm until I came to a complete standstill for about 5 seconds, then it would slowly come down. However if I start the car up and let it idle for about a minute before setting off it very rarely happens.

Cleaned the valve really thoroughly a year ago. Mine is pretty much like that though so I will clean again. I also have a new gasket ready to clean the throttle body

I'll update after drive home