[Mk2] [NA] High idle (1500-2000rpm) - Can't work out what is causing this.

[RobPhoboS]

Hey guys,

I've been consistently getting a high idle speed after my car has warmed up a bit (15-20mins), with a bad mix of fuel it seems. Last night I replaced the ECU Water Temperature Sensor.
This has made the car run a lot nicer but the problem still comes after some time.

I previously checked for an air leak but really couldn't see or hear anything, I tried spraying the pipes with WD40 to see if the idle made a little change but it didn't. (this was done both cold and warm engine)
Now obviously it could be an air leak which only happens once the engine bay is hot, and the pipe flexes a bit or something.

No ECU error codes either.

[toxo]

Could be sticky ISCV? They usually stick shut but I don't see why one couldn't stick open...

[RobPhoboS]

Forgot to add, I did take it off and clean it up as a precaution but didn't do anything.

It's only when it's warm.
Very odd.

Anything else I can do with the pipes to test ?

[RyanRs]

check all your small vacuum lines. a leak in any of them will raise the idle.

Also i found that when i cleaned up my ICV, i had to make a new gasket up for it. Get a can of carb cleaner and spray it about the ICV. if the engine starts coughing then thats where the leak is

[black gts]

i get high idle when hot .
tried most things ,leaks,icv replaced , carb cleaner on every thing, no air leaks,oxy sensor,checked timing ,even but oem bov back on.
put my apexi pfc on and the idle is spot on, here is my thoughts on it,
1 oem ecu has been tweaked/altered
2 oem ecu is set up for different cliamte
3 decat /custom intake pipe and the breathers on the engine have been changed
other than that my idle problem can stay

[RyanRs]

no it wont be any of them.

1, is impossible 2, you car is from japan right? like most of everyone else's turbo mr2 in the uk. that would also suggest that your idle would change as you drove to different locations! 3, this does not effect your revs.

Ok This is an idea, consider this...

When the engine is cold, on a perfect working engine the ICV is around 90% open so the ecu can hold an idle of 'about' 1200 rpm. when the engine is hot, the ICV is only open about 20% enough to keep the revs at around 900.

If you have a vacuum leak, while the engine is cold, the ecu will not open the ICV to 90% like it should as it will detect the high idle rpm as being too high, instead it will open just enough to make 1200rpm 10% say? Therefore you will not notice that you have a vacuum leak while its cold. But when the engine warms up and wants to set the ICV back to 20% (its warm open state,which will usually drop the idle from 1200 to 900) the revs then actually Increase instead of drop.

hard to explain but do you see what im saying?

Your PFC's may be setup to control the ICV differently, or it may have been calibrated on there while you had the vacuum leak.

Therefore my verdict is. Vacuum leak.

[RobPhoboS]

Is it possible to just buy a replacement hose kit for my N/A then ?
I'd rather do that and have new hoses anyway.

[ashley]

Your PFC may have been calibrated on there while you had the vacuum leak.

Therefore my verdict is. Vacuum leak.

+1

[RobPhoboS]

I've just come back from T.GT did a few quick things but still not resolved:
A clip wasn't quite on for the brake servo.
Sprayed some maintenance spray into the pipe that connects to the air intake tube, and also covered it so it stalled the engine (I guess to check the ISCV).

Any other thoughts as I can't get through to them on the phone at the moment ?

[toxo]

Has your car got air conditioning?

[RobPhoboS]

Has your car got air conditioning?

Yep, it an import.
I use the AC every so often but rarely.

[toxo]

The aircon system has an idle up VSV which raises the idle when the aircon is in use. I'm clutching at straws now though

[RobPhoboS]

The aircon system has an idle up VSV which raises the idle when the aircon is in use. I'm clutching at straws now though

Would that on affect the idle when the AC is on ?
I did read that on another thread with a similar situation but not sure what the resolve was on his car.
The hoses on my car seem fine, aren't perished or looking bad.

[toxo]

It's supposed to affect the idle when the aircon is on when it works properly. If it had stuck open it would have the same effect as the ISCV sticking open... ie letting in more air than is intended and thus raising the idle. Easy way to tell would be to engage the aircon and see if the idle raises even higher.

[RobPhoboS]

I'll give it a check later for that

Let's just say for now, that it's not going to be that
One of the chaps at T.GT said that if the intake throttle body had been taken off, just be careful that the gasket had gone on flush, and hadn't kinked.
I'm fairly sure that when I had taken it off, there wasn't an issue with the gasket bit.

[toxo]

FWIW I don't think it will be the aircon VSV, it's not big enough to raise the idle as high as you are reporting. Like I said, clutching at straws!

[Ozmondo]

i had a high idle, as a previous owner sped it up to pass MOT emissions. so just turned it down with an allen key. might be completely unrelated to your idling problem but just thought id mention it.

[RobPhoboS]

Right, I went up to Pacific Works today, my TPS wasn't working quite right, so put a new one on and cleaned up the throttle body & gaskets.

BUT


When I got back to London -
It did it again - noooooooooooo

[alan wheeldon]

My advice is dont worry about it... it works dont it

[black gts]

just a thought
is the butterfly fully closed. because i had taken the slack out of my throttle cable and when doing mataince on the car i moved the cable out of the clip its in and that had opened the butterfly , only a very small amount but it went upto 1900rpm
just incase mate