Low temp & high idle

[enzomorales]

Hi, I've noticed that my '91 rev 1 n/a MR2 is taking longer to warm up and the temperature gauge is staying very slightly below what was previously normal. Also, the idle speed is slightly higher at around 900-1000rpm instead of previous norm of 800rpm.

Any ideas what this could be and whether this higher idle speed would effect an MOT emmissions test, which my car recently failed....

Thanks.

[MartG]

Sounds like it could need a new thermostat

[raptor95GTS]

Sounds like it could need a new thermostat

aye good bet. How warm are the heater / radiator pipes

[enzomorales]

Just been out driving the car again and the only difference from normal is that the car takes longer to fully warm up (a tad over 10 minutes normal driving) and idles higher until its up to temperature - heaters and everything appear to be operating OK. Car previously warmed up much quicker - say 5 minutes or less of driving, maybe this is not a big issue ? but wondered if it might have anything to do with high emissionins during MOT test. Cheers

[matt_mr2t]

When the water temps are cold the car will idle high (about 1,250rpm to begin with) and the cold start injector will add even more fuel.

This applies to rev1 and rev2 turbo's but as yours is of the same age and probably has an AFM it may be the same.

Did you own the car last winter - the temps are dropping a bit and it would be normal for the car to take a little longer to warm through. If it doesnt warm up after about 15 minutes of being driven then look to changing the thermo.

[Turbo-G]

Sounds to me like the thermostat is beginning to get slightly stuck open. Change the thermostat, and I guarantee your car will warm up much quicker than you have ever seen it, and you will also notice that the car will come off cold idle much earlier too. Tried and tested last weekend by myself.

HTH..

[enzomorales]

Thanks for feedback everyone. Was buggin me a bit that it might be a temperature sensor but I agree with advice here and will look at replacing the thermostat.

I understand there's two temperature sensors (one for ECU and one for dashboard guage). My logic in thinking it's not a temperature sensor was that if they are both showing similar symptoms of low temperature (ie. high idle 'cos of low temp on ECU sensor and low reading on dash gauge 'cos of guage sensor) then they are likely to be reading correctly and the cause of low temperature is thermostat stuck open in some manner....

....then the doubts started again when I though my heater was rather warm for the temperature gauge only having just got to the "C" mark....think this is just paranoia though.....

Finally (and this has only happened once) the car was stationary and almost at normal temperature (still never quite gets there), when I put the heaters on full blast, the temperature gauge dropped from half way to about the quarter mark... it only done this once and I couldn't recreate it again although I occasionally see a fractional drop on the temp. gauge when I'm travelling at speed. I guess these are other pointers to a failing thermostat. Cheers

[Canopus]

After start up and normal driving for a few mins if the heater is put on its normal for the temperature guage to drop as the heat in the engine is being used in the heater matrix. The engine temperature should then quite quickly climb back to normal as the thermostat is registering a drop in coolant temperature in the engine and closing until the coolant heats up again and the status quo is restored. I would suggest this is showing the thermostat is working okay.

Mine has done this ever since I bought it nearly 4 years ago. In terms of general cooling as the temperature drops it does take a lot longer for the radiator to get warm as there is a lot of coolant in an MR2 compared to a normal car. My car has always idled high, typically about 1000 unless its a very very hot day in which case it drops to about 800. On cold start up the ide speed is about 2000.

Hope this helps.

[Turbo-G]

Yep, still sounds exactly like a stuck open thermostat to me, get it changed mate

[Leon.]

typically about 1000 unless its a very very hot day in which case it drops to about 800. On cold start up the ide speed is about 2000.

These are a bit high tbh, when warm you should be idling around 800-850rpm. Your cold start up seems very high, mines never much above 1250, unless its super cold then maybe 1400.

Your profile doesn't say which model you own.

[Canopus]

I agree the idle speed seems high, particularly when starting from cold at about 2000 but its always been that way ever since I bought it. Its a MK 2 version one (Jan 1992) 2.0 GT NA T-Bar.

Its always passed the MOT so far so the emissions are okay. but is there a way to reduce the idle speed? - Sorry if I'm hijacking the thread - not intended.

Geoff

[Leon.]

Sounds like sensors need looking at, and maybe your thermostat. How are you iggy components, plugs etc?

[mr2ster]

i fitted a blueprint thermostat to mine last week , it cured my tick over problems. mine was not stuck open , its was just opening too soon so the coolant never ever got to a temperature high enough to lower tick over revs.


also if you look on the top of the throttle body , you should see a small black rubber bung, under it is a screw , if you screw it in your revs will die down , turn it when the engine is hot though.