Passed MOT, But revs need revising.

gavin.starr · October 04, 2011, 08:06:37 AM

I have finaly finished my project and have got it on the road woop woop.

But im having a small issue with the revs.

Some times when i come up to a set of lights rolling up to them in gear, i depress the clutch when neering the line as you do in any car, but the revs will stick at 1500 rpm, if i give the throttle a blip it drops to around 800rpm which is normal, could this be to do with one of the small micro switches in the throttle body?

After it has then been sat for around 10 seconds at the lights the throttle will drop off to just below 500rpm and nearly cuts out, but then it realises and puts the revs back up to 800rpm and repeats and repeats and repeats until i set off again.

Its fine when it cold it only does this once its warmed up.

Can anyone shed some light on this for me.

Cheers in advance

Gav

ctothey · October 04, 2011, 08:40:11 AM

Mine did similiar to this a lot of the time.
turned out the closed throttle switch had excessive resistance/open circuit.
changed the switch. good as new.
its only a 3 pin plug on the tb, so relatively easy to diagnose.
cy x

gavin.starr · October 04, 2011, 09:01:27 AM

Can you provide any more info on how you tested it, unfortunately electronics is not my strong point.

samg40 · October 04, 2011, 09:26:08 AM

Have you tried adjusting the idle screw in the throttle body?

Well done on getting it on the road by the way.

hayesey · October 04, 2011, 09:37:51 AM

is it a standard throttle body or a bored out one?

Justin14100 · October 04, 2011, 09:38:24 AM

there is also a throttle stop screw / nut which it could be worth playing around with.

gavin.starr · October 04, 2011, 10:18:49 AM

I have fiddled with the stop screw but to no avail.

Where abouts is the idle screw inside the throttle body, have you any pics. Im relitivley now to G40's so pics speak a thousand words as im still learning.

As far as im aware the throttle body is standard although it has been de-wedged if that makes any diferrence to idling

gavin.starr · October 04, 2011, 01:02:08 PM

I know what you mean about the idle screw in the throttle body something has just jogged my memory, im at work at the moment so i cant fiddle with it until i get home.

which diresction opens the throttle, clockwise or anti-clockwise?

Cheers in advance

Gav

hayesey · October 04, 2011, 01:54:36 PM

clockwise closes the screw, anti-clock wise opens it. You need to put the ECU into service mode to do this by disconnecting the blue temp sensor while the engine is running. Then set the idle and plug the sensor back in again. All with the engine running.

It could be that your throttle plate is sticking open though which is common with bored out throttle bodies with aftermarket made throttle plates. If someone has de-wedged it they might have removed the plate and it's not quite located correctly or it needs a clean or something? But I'd try setting the idle screw before doing anything else.

gavin.starr · October 04, 2011, 02:09:46 PM

Cheers ill give it a try when i get in.

Is it safe to be plugging and un plugging connectors whilst the engine is running?

Im i to start the car and the unplug the temp sensor, or to unplug and then start the engine or does it not make any difference at what point its unplugged

Gav

hayesey · October 04, 2011, 03:07:28 PM

yes, that's what you have to do

Jezza-7 · October 04, 2011, 06:00:44 PM

Quote from: gavin.starr on October 04, 2011, 02:09:46 PM
Cheers ill give it a try when i get in.

Is it safe to be plugging and un plugging connectors whilst the engine is running?

Im i to start the car and the unplug the temp sensor, or to unplug and then start the engine or does it not make any difference at what point its unplugged

Gav

Just dont burn your hand when unplugging or reconnecting it as it hurts.

gavin.starr · October 05, 2011, 11:51:28 AM

I have sorted the idle out, but now instead of fluctuating between 500 and 800 rpm. Its now doing it between 800 and 1100 rpm.

the sticking throttle has sorted its self out but instead of sticking it revs from 800 to 1400 rpm until i blip the throttle, then it drops down to idle and after about 10 seconds starts the fluctuating from 800 to 1100 rpm as described above.

Is there some where else i should be taking a look at Ie fuel pressure regulator. Boost leaks etc...

Gav

samg40 · October 05, 2011, 12:25:38 PM

Mine used to do exactly that until I tweaked the idle screw on the throttle. Sounds like you might have done it a bit too much the other way.

jonathan g40 · October 05, 2011, 05:48:14 PM

Try the lambda sensor my g40 did that and the lambda sensor cured it idles perfect now