Hi my 92 eunos 1.6 only idles at 900 rpm when it’s warm and temp gauge is near half way . I known it’s going to idle fast when cold but on a cold day the temp struggles to get near half way so it always ticks over at 1500 rpm .can owt be adjusted so it idles lower when cold . Regards Bob
New thermostat needed by the sound of that
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The thermostat point is clearly worth looking into. However, isn’t it usual for the normal (warmed through) idle speed to be achieved well before the thermostat comes in to play? Presumably there are people on here that will know that? Is it purely driven by a certain coolant temp having been reached, or are there other conditions that play a part? For example, on my 1980s BMW I’m pretty sure the normal idle speed is achieved after a set time interval rather than by reference to temperature, or maybe a combination of the two?
Find out exactly what the trigger(s) is(are) and that will then lead you to the solution.
The thermostat prevents water circulating through the radiator until the water reaches the set temperature and it will continue to restrict that flow until it opens fully.
If the engine then cools again the thermostat will close and open accordingly.
If the thermostat is stuck open the coolant will not warm up to full operating temperature in cold weather, so the sensors will enrichen the mixture etc accordingly.
It was commonplace to blank off sections of the radiator in winter back in the day
Maybe 80s BMWs had injection in the 80s but ordinary cars had carbs I think.
but a normal temp in the engine will not be reached if the thermostat is sending the coolant to the radiator before it needs to
Exactly
Fuel injection on mass produced cars was relatively commonplace from the late 60s onwards.
The key question is what triggers the transition from fast to normal idle. On early MX5s it may well be down to measured coolant temps having passed a certain threshold. But can someone definitely confirm that? And if that is the case, at what temperature?
Replacing a permanently stuck open thermostat may well be the solution in this instance, but maybe it’s a faulty temp sensor either instead or as well?
It’s pretty simple to determine if the thermostat is stuck open - do I need to spell out how to do that?
If it was a faulty temp sensor the problem wouldn’t only occur on cold days (See original post)
If I leave it to tick over stationary the idle speed drops to 900 rpm before mid temp is reached but as soon as its driven the idle increases again to 1500 and whilst driving stays at 1500 until mid temp is reached so I don’t think it’s purely coolant temp sensed.
On the NC (the only version I have any familiarity with) the idle speed will increase when the clutch is depressed. Is the same true on earlier models? If so, could the activation switch be kicking in when it shouldn’t?
Please just change the thermostat!! It’s not expensive
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I put a new stat in left it to idle after a few mins it was at 1000 rpm with temp gauge at a quarter way up , as soon as I pressed clutch in revs were back up to 1500 and stopped there while it got to half temp ? Why would a clutch switch have such an effect on fast idle , can it just be disconnected ?
Hi Bob, I’m also running a 1.6 '92 Eunos and (although I’ve only had it about 6 months) its always had a cold idle of about 1500rpm when I first start it up and until its warm (especially if I’m also running the lights / heater on) and I had just assumed that was how it was meant to warm up (as my motorbike does a similar thing). We may both have the same problem or it might be normal, I am now questioning my own car!
It does make it easy to drive from cold Nathern but seems to fast idle for for a long time . If it’s correct and working as it should I might just get a grill to reduce air flow so perhaps it will warm up faster . My wife had a mk2.5 years ago and that definitely didn’t fast idle for so long but that was a 2005 so may have a better cold running system
The original 1.6 model has the thermal “wax” valve on the side of the inlet manifold to let in extra idle air while the engine is cold. It has small coolant hoses going to it so it warms up as the coolant does and that should make the valve close up. Yours may not be closing properly and a stuck-open thermostat may be making that problem worse.
I had a similar problem with my first 1.8 (in that model the wax valve is relocated to under the throttle). In my case I think I strained the valve by exposing it to supercharger boost pressure but the result was a very high idle that only diminished when the car got fully hot.
Tried it today, just left it idle on the drive after a few mins the idle goes down to 900 rpm so cold idle system seems ok , but as soon as clutch is pressed down its back to 1500 rpm . Is it ok just to disconnect clutch switch ?
Before you try this have you reset the base idle?
What does the car idle at without the ecu? You need to pin out the ecu by putting a wire between GND and TEN in the diag plug box. Then set the idle
I wouldn’t fiddle with the clutch switch. That would be a bodge to hide a symptom instead of fixing the actual problem.
If I understand correctly the car was idling okay around 900 rpm but simply pressing the clutch pedal made the revs jump to 1500 and they stayed high when you released the clutch again? If so then I think the problem is not with the wax valve but with the Idle Speed Control valve. The ISC valve is under the throttle and it’s driven by a solenoid controlled by the ECU. That’s the only thing I can think of that could make the revs jump up like that. My guess is the valve is a bit gummed up so it tends to stick open. You can clean these with a bit of carb cleaner spray or similar. It’s dead easy on the Mk.1 1.8 version though I’m less familiar with the 1.6.
I’ve had this on my old 91, it was caused by a leaky radiator. There is a valve in the intake system that allows more air through when cold via an open duct (sorry can’t remember it’s name off the top of my head). It is controlled by coolant temp and when the coolant level dropped, it filled with air and wouldn’t shut the additional duct when the engine was hot resulting in a very high idle (approx 1800rpm). If your coolant isn’t getting up to temp because your thermostat is permanently open, this valve may not be closing. It’s just a thought. If the engine is getting up to temp in warm weather or when sitting in traffic, then cools down at speed its likely to be the thermostat. They’re quite inexpensive and easy to replace on an NA. This is all from memory so apologies for being vague, but there is a chance that the thermostat replacement will solve the problem.
I’ll try these fixes thanks for all your reply’s much appreciated