Hi all,

2007 Hawk STi
Been having this issue for about a week...
On cold startup, the idle goes straight to 1800 - 2000 rpm, which is high, certainly for this car anyway, never seen that before. It then drops to around 1100 rpm, after about 20 seconds I drive off, and as soon as I touch the throttle, it goes back up to 2000 rpm, and rev hangs about 1500rpm through the lower gears. It seems to improve as the car warms up a bit.

No codes, no CEL. No battery light.

Thinking it was perhaps stuck open slightly, I tried cleaning the DBW throttle body (so no IACV)
I've also tried two ECU resets via my PSI3 data monitor - nothing changed. Then did a hard reset by disconnecting the battery for about 45 mins - this helped on the first drive and thought it was fixed, but tonight on stone cold it behaved the same.

I've sometimes (not all the time) noticed a fuel smell at hot idle at the tailpipe after a run, I'm pretty sure it's running rich. The idle can hunt a bit on a hot start too. I think the CAT was pretty toasty a few days ago because I could smell a faint eggy smell.

I did notice that when I re-connected the negative terminal last night and fired it up, the battery voltage on the PSI3 was on or around 12v whilst running...usually should be 14.2v or therabouts.
Also tonight, the BV once warmed up seemed to wander between 13.5v and 13.9v whilst driving, lights on, heater fan on etc. Is my battery perhaps toast and is causing poor running?

It's perhaps 18 months old the battery, Yuasa, but has gone proper flat 3 or 4 times from just not being driven. The green ball in the window has dropped a few inches, it looks like it's sitting at the bottom of a tube - whereas I think this should be floating at the top? Or are these floating ***** a load of nonsense, they only show you one cell anyway?

I've now connected my Ctek and using the recondition setting in the hope to perhaps rescue the battery, but would a knackered battery cause something like a fast cold idle, use a lot more fuel and generally run "off beat" ?
If my battery is indeed toast, I guess it wouldn't power sensors enough for the ECU to make much sense from?

There's no slow crank just to mention, it cranks normal speed as far as I can tell, not a sluggish crank by any means.
The alternator belt seems tight enough, no screeching when damp etc. The main terminal is tight.

 

I recommissioned my 2 year old Yuasa ( a record age for me) this week, after going flat once, with a Ctek. The green ball came back, but under load it was toast at 10.8V. Had to go to MOT with jump pack.
I sure you know, but A/C makes idle jump about a bit too.
Currently waiting new one from gsf ( jamjarcars) but not hopeful of its arrival due to Evri being courier.

 

Was that 10.8v without the engine running and just stereo / lights on etc?

 

10.8 after it was hitched up, no lights just ignition, being over 12 after charge. Once they're gone they're gone!

 

Thing is though, it cranks totally fine, surely a duff battery would crank slow....plus alarm chirp etc - things I've had before from a dying battery.

 

CTS. Coolant temp sensor.

 

Have you seen CTS cause this?
Wouldn't that give me a code?

 

Also clean you Idle control valve

 

Thanks Rig.
I don't think DBW has that, I can't see it on the throttle body - I know the part you mean, but mine doesn't have it...

 

Id still be cleaning the actual throttle body butterfly inside the TB as its clearly sticking/stuck at delivering the higher rpm at cold start

 

Just did a cold battery test, engine off it read 12.7v so it's holding a charge, then cranked it and it showed for a millisecond 10.6v then straight to 14.2v
I wonder if this voltage drop of 2.1 volts is momentarily "wiping" the ECU memory for throttle / MAF settings so it makes the fast cold idle to keep everything safe? No codes, no CEL.

Any suggestions if the battery is past it's best?
Another observation, hot idle dips if I pull the window switch up if the window is already closed, yes a very slight dip is expected and normal, but this feels more pronounced than normal, like the battery has no buffering to cover the extra load. Starts the car fine, but perhaps no real steady voltage depth in the actual plates of the battery?

 

don't forget you have smart charging alternator so a slight dip in voltage is expected hence it then detects and starts charging

looks like you want it to be the battery lol so buy 1 and see if it is ha

 

I've already done that, now spotless, but has made zero difference....
ECU resets, hard reset by disconnecting the negative terminal on the battery for 45 mins, hasn't helped.

 

Or connect battery to Yours from other running car ,than start Your car and check.

 

I've already done that, now spotless, but has made zero difference....
ECU resets, hard reset by disconnecting the negative terminal on the battery for 45 mins, hasn't helped.

 

All that job instead of connecting battery from other car,wow

 

I don't have easy acecss to other batteries.

 

Put another earth wire on , straight from the battery negative to the engine block , could be a bad earth , I've had that at least twice on cars , so all my scoobies have an extra earth wire