On my 2001 XKR I have been noticing lately that when starting from cold with ambient temperatures in the region of 17-18°C the car first revs up to an indicated 1400RPM approx, for 20 seconds or so, before dropping back down to a normal idle speed.

I've seen the TSB that states that in the 20°C range normal RPM is increased by 220 RPM for 20 seconds, which makes 1150rpm. Even allowing for my rev counter to be over reading, it does seem quite high.

There are no codes on the engine, long term fuel trims aren't particulary high, the car has had new spark plugs, the throttle body has been cleaned, the MAF sensor has been cleaned and so on, so does anyone have any suggestions as to what could be causing this, as I really don't like the car reving so high from a cold start?

TIA

 

Mine idles high for about 20 seconds when cold, perfectly normal, i use that time to let it warm up a bit. I guess I could drive away, but I prefer to wait till idle drops, usually 1200-1400 or so rpm

 

I've been working on my car a lot recently and disconnected the battery each time for safety. After an extended work session, I noticed that when I reconnect the battery and start the car from cold, the initial engine rev is a lot higher than normal, then settles down quickly to around 1400rpm and then down to idle. However the next time I start the car, the initial rev is only 1400 for approx. 15sec and then settles down to idle.

I never start driving the car until the idle rpm speed is reached which isn't long in Bahrain as it's quite warm.

 

 

 

+1

It's relearning -- battery off clears the learned values.

 

+2 Zray

@dibbit OP -- what you are observing is most often caused by dripping injectors. try some Techron fuel cleaner 2 or 3 times before your next oil change, one in each tank of fuel before filling, run the tank to 1/8 before next. this might make a difference. otherwise, having the injectors serviced is not very costly and they are easy to remove.

 

I'm pretty certain the throttle is correctly adjusted, but I will check the value just in case. This is only happening now due to the winter temperatures - during the rest of the year the ambient temperature is high enough not to be in the elevated idle range, so I'm not sure if anything else has changed since last winter.


I did try a can of BG44K last year, which made a difference to the smoothness of the engine - do you think it's worth trying more cleaner?

 

Also, some have reported that after disconnecting the instrument cluster, some gauges were reading off (needle offset somehow). I believe a "hard reset" cures these problems. Maybe a weak battery is somehow making your tach a bit off. If you are OK dealing with OBD monitors needing to set again, try the said "Hard Reset" and see what happens.

Separately, the real rpm value should be available over OBDII for confirmation A cheap ELM327 will read this.

Best of luck, keep us posted.

 

Thanks for the suggestions - I might try a hard reset tomorrow just to see what happens. The rev counter is reading accurately - it's showing the same value as over OBD.

I've attached a screen grab from Dash Commander at idle when warm for info (short term trims around 0%). The throttle position was reported as 2.7%.

 

LTFTs are quite big. If they drop when revved you've an air leak.

 

yes, try the Chevron product, the large bottle. then check for air leaks, VVT seals, oil cap, etc. using an unlit propane torch once the engine is at idle is an old trick.

 

Reiterating what others said above, if you're disconnecting the battery, the ecm is having to relearn when you start it the first time. That initial high idle is absolutely what you would expect to see each time.

If you continue to have that problem every time you start afterwards without having disconnected the battery again, then you perhaps have an issue.

A slight leak in the intake system will cause an initial high idle until the trims correct it.

 

I'm thinking I will definitely try a few tanks of injector cleaner. The car is an XKR, so to remove the injectors the supercharger will have to come off, which isn't something I really want to have to do.

Thanks, but I'm not disconnecting the battery, that is someone else on the thread. The battery is new, so I don't think this is somehow being caused by a weak battery, although the symptoms do match.

 

Do you mean the actual LTFT values should drop, or the STFTs should go negative? When I rev the engine, there is little change in long or short term values.

 

If the LTFTs stay at such big numbers you're looking for some other issue than an air leak.

Could be a fuel supply problem or an exhaust restriction (blocked cat), for example.

 

Thanks. Today both LTFTs were at about 5% after driving the car. I changed the fuel filter last year - I intend to check the fuel pressure once I've got myself a gauge that fits the schrader valve - its on the to do list.

 

I'm suffering the same issue on my XK8 4.2 and i assume it developed over the years. Now it takes about 40 secs till the idle speed drops from initial 1400 to first 1100 and then 900 and 650 when warmed up. I dont like to shift the gear in as long as the engine revs at 1400.

I don't think that it is caused by leaking injectors or false air because if so you would recognize other issues as unstable idle or warm start problems. i've checked the coolant and the intake air temperature sensors by resistance measuring and found them in good working order. my clue is now that the EMC is supposed to elevate the idle speed in order to get better emission results by warming up the catalysts faster. maybe this is an result of worn lambda sensors.
​​​​​​I have a lack of phantasy to see other input signals that could cause the EMC to lift up idle after cold start.

Fritz

 

Someone suggested to me that this could be an early symptom that the valve in the EVAP Purge canister could be on the way out. Error code P0445 on the OBD when it goes. Access is easy via the front left wheel well liner and simple to replace. Part is inexpensive as well.

It's better/cheaper than replacing the CATS which needs dismantling the exhaust.

 

one variable that might be relatively easy to check is how long before the car enters closed loop. my pc based scanner does this. regardless of the ambient temperature or how long since the engine was last run my car enters closed loop very quickly. have not timed it, but seems less than fifteen seconds. i tested this on another XK8 and it was the same. if yours stays in open loop longer, we might better know how to escalate.