Idle control problem - help needed

[munter]

Hi,

I have an import Supercharger. The first ten minutes of driving the car idles at around 1300 rpm before dropping to 800 rpm when warmed up. It's my daily drive right now and my commute is ten minutes through town. The car is noticeably burning the fuel at a crazy rate until warmed up and it's costing a fortune!

I've located the idle control screw but it's fully turned clockwise. Turning anti-clockwise has the opposite to intended effect of increasing idle revs!

What can I do to get cold start idle to 800 rpm from the get go?

Thanks
Paul

[boondougal]

this has surely got manual choke conversion written all over it...

search for it and you should get the answer.

As with alot of things though these roads will lead back to woodsport!

[PW@Woodsport]

Paul, our manual choke kits won't work on the SC, but just leave it for now, i'll take your idle speed control valve apart when the car is here and sort it out for you.

[Lauren]

this has surely got manual choke conversion written all over it...

SC doesn't have a waxtstat, it has proper idle control.

Paul, what your car is doing is absolutely correct. Be thankful you don't have an NA where the initial idle is around 2000rpm!

You can't have a cold idle of 800rpm, it just won't do it.

[munter]

Thanks for the feedback. So what you're saying Lauren is straight off the production line the SC's all idled at 1200-1400 cold? That seems pretty bad even for the 80's!

There is a little bit of a surge in revs as well when you come to a stop and
put the car in neutral. I'm not convinced it was designed to do that.

Any other tips for fuel saving on short trips much appreicated!

P

[SuperRedMR2]

I've only just found out recently that when you come to a stop and put your foot on the brake, the revs increase which is perfectly normal. Electrical activity will increase the revs, i'm assuming that happens with the superchargers as well as the n/as

You're lucky yours doesn't rev at 2500 RPM when its cold like mine!

[elbon50]

Thanks for the feedback. So what you're saying Lauren is straight off the production line the SC's all idled at 1200-1400 cold? That seems pretty bad even for the 80's!

the N/A idles a around 2K till the waxstat warms

[010on1986]

My sc cold idles at around 1200-1300 for a couple of minutes, I usually put the heater on cold and it warms up alot faster, guess it has less water to circulate and heat up intially with heater on cold.

[Lauren]

Thanks for the feedback. So what you're saying Lauren is straight off the production line the SC's all idled at 1200-1400 cold? That seems pretty bad even for the 80's!

There is a little bit of a surge in revs as well when you come to a stop and
put the car in neutral. I'm not convinced it was designed to do that.

Any other tips for fuel saving on short trips much appreicated!

P

Yes. Honestly you need to go in an NA car. Mine idles at 2100rpm for the first few minutes. It's not bad at all. 1200rpm or so really is nothing in comparison.

I can't get my idle below 1100rpm as it gets too lumpy with my cams, so think yourself lucky!

As you have an auto and no engine braking you'll use the brakes more. Pushing the brake pedal will momentarily increase the idle. You can see this by pumping the brake when the engine is running.

I think probably best to accept that it's not going to match the figures of today's cars. I use my car daily. I get around 35mpg or so with a mix of motorway and A-roads commuting daily. I only get good figures though because I do a bit of a motorway driving when I sit behind the trucks doing 87kmh which equates to 3000rpm in 5th

The auto has intergalactic gearing in over drive, so any long journey you can stick it in over drive and do minimal revs which makes for comfy cruising.

[Lauren]

I've only just found out recently that when you come to a stop and put your foot on the brake, the revs increase which is perfectly normal. Electrical activity will increase the revs, i'm assuming that happens with the superchargers as well as the n/as

Always thought the revs increase as a result of the servo being connected to the inlet, so pumping the brake may pump air into the inlet.

[PW@Woodsport]

I've only just found out recently that when you come to a stop and put your foot on the brake, the revs increase which is perfectly normal. Electrical activity will increase the revs, i'm assuming that happens with the superchargers as well as the n/as

Always thought the revs increase as a result of the servo being connected to the inlet, so pumping the brake may pump air into the inlet.

No it's due to the idle-up VSV supplying more air to the inlet, if you think about it the brake servo cannot do that, there is nothing going to atmosphere at the servo end, it's sealed. The ECU has a STP input, so knows when the brake pedal is being pressed and opens the idle-up VSV.

[Lauren]

You may improve the idle somewhat by cleaning up the ICV. Always worth a try.

[PW@Woodsport]

Paul if you actually do want a lower cold start idle then that is something i can do for you, it's not impossible at all, leave it with me.

[munter]

Thanks Paul,

Yes if something can be done to lower the cold idle that would be great. Most of my driving will be short 10 minute journeys and if I can improve fuel consumption a bit then it will be more cash for long country drives at the weekend!!

cheers

[PW@Woodsport]

Not a problem, i can do that.

[JMR_AW11]

I've only just found out recently that when you come to a stop and put your foot on the brake, the revs increase which is perfectly normal. Electrical activity will increase the revs, i'm assuming that happens with the superchargers as well as the n/as

Always thought the revs increase as a result of the servo being connected to the inlet, so pumping the brake may pump air into the inlet.

No it's due to the idle-up VSV supplying more air to the inlet, if you think about it the brake servo cannot do that, there is nothing going to atmosphere at the servo end, it's sealed. The ECU has a STP input, so knows when the brake pedal is being pressed and opens the idle-up VSV.

Hi Paul
I can't remember for sure because I haven't looked at the UK mk1 ECU pinouts for years and years but I didn't think the UK ECU knew when the brake was being pressed.

I no longer have the ECU stuff on this PC so I can't check but I didn't think the UK ECUs had the STP connection from the brakes.


I think the car does the brake controlled idle up control directly via a diode from the brake light wiring?

However, I'm only about 80% certain

[JMR_AW11]

Don't take this as gospel but I thought the idle up valve had multiple inputs from the wiring harness.

Each via a diode so if you turn on the heater fan or the lights or press the brakes the idle up will be enabled via the respective diode connection.

It also has a control line from the ECU and from memory (on the late model mk1b) the ECU holds the idle up valve ON for a few seconds after startup.

[JMR_AW11]

The UK mk1 ECUs also have an auxilliary 'idle up' control written into the program code that achieves idle up through adding controlled bursts of ignition timing advance.

This must have been added by concerned Toyota/Denso engineers when the development TCCS kept stalling at junctions if there was a load on the engine like turning on the lights at idle with a hot engine.

The ECU can sense a sudden drop in engine revs at idle and tries to stop the stall by giving a sharp shot of ignition timing advance

[jimi]

I think the car does the brake controlled idle up control directly via a diode from the brake light wiring?

That's the way I thought it worked and according to the diagrams I have it is the way it works.

[coverco]

Steady on chaps, Paul Woods knows everything about Mk1 MR2s and is never wrong