1500rpm idle and dodgy temperature gauge

[Bogalog]

Hi all,
Just purchased my first MR2 (coming from a Eunos) and I love it, but it has some things to work on.

The current job is to fix the coolant temperature gauge, which does move off the bottom, but only to the cold position (i've never seen it go above 1/4). The engine does seem to warm up fine
Possibly related is my high idle, which varies between 1400 and 1600, though it's nice and smooth running

 The previous owner had the throttle body cleaned out 3 months ago so my next guess is the engine coolant temperature sensor, or the sender. Is there a way to check the gauge functions normally?

Thanks

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The fix ended up being a new temperature sensor. Thanks all

[Joesson]

My first thought was a faulty/ sticking thermostat.
If you search for "thermostat position" you will find references to similar symptoms to yours.
Mr Zwei says to remove thermostat and check it in a bucket with some boiling water, if it opens when hot and closes when cold then it is OK and you need to look elsewhere.

[Bogalog]

I had the belt go and the engine start to overheat, and even then the gauge was not showing a problem. Also, the idle seems completely unaffected by the engine temperature - it is the same after a long journey
I will look into replacing the thermostat as it may be contributing to the problem?

[jonbill]

The idle problem might well be your idle air control valve sticking or maybe the throttle isn't closing completely - possibly not put back right when cleaned.
If you have an obd app like torque or dash command you can see what coolant temp sensor is reporting, that might help determine if there's a gauge problem or not.

[Carolyn]

+1 on the idle air control valve.  Just 'cos the throttle body has had attention, it doesn't mean it's been done properly....

Jonbill just went through this one and he sorted it with a good go at the throttle body.

[Bogalog]

So far I've:
Taken apart and cleaned the IAC, you were right that it hadn't been done
Attempted to get it back together, only to realise the rubber gasket is too big now - anyone know where I can get a new one? Eurocarparts had nothing as far as I could tell
Attempted to use gasket sealant to fill the gap (coolant leak)
And now I'm waiting for another sealant attempt to cure

In the meantime I was checking the lack of a CEL and found that a previous owner stuck a load of black tape in there! Hope I haven't bought a lemon

[Carolyn]

The gasket has swollen because of the carb cleaner.  Leave it overnight, it will shrink back.

CEL?

[Bogalog]

Check engine light. Happily enough it didn't come on when I started it up, but the second attempt at the gasket failed so I'll try again tomorrow.

Thanks for all your help everyone

[spit]

If you can't wait and you still have that fragile gasket...... Last time we experienced a swollen IAC gasket, we cut a small piece out with a blade and blobbed the join with a little sealant. Works well if the rubber doesn't shrink back fully on its own, and if you pick a less critical point for the join it does no harm.

Reseal should be easy enough but you need to ensure that any old sealant and crusted coolant is removed from the gasket seat or it'll carry on seeping.

[Bogalog]

About to try for the 4th time. The old gasket is a perfect fit now, but in 3 pieces. I've been cleaning it out every time and it's taken up most of my day. If that doesn't work I plan to just bypass it for now. Not ideal but hey, it's my only car and I need it running asap

Update:
Well it has a very small leak still. But I think it's driveable, it made it to the local b&q and back (about 3 miles each way). The check engine light came on, but it was probably on before judging by how it was blacked out previously. The code is P0141 which I see is 02 sensor bank malfunction. Am i in need of a new O2 sensor?

[cabbydave]

Try changing the temp sensor as it controls the tickover in the ecu as well

[Bogalog]

Update:
Got an obd2 reader with wifi, it seems my coolant temp doesn't break 120F, so I assume a new thermostat is in order

[Carolyn]

Or your sensor is no longer accurate.

A used throttle body might help with the gasket issue.

[Bogalog]

Just wanted to say thanks for all the help, fitted a new coolant sensor and the idle is dropping down nicely as it warms up.
Luckily the gauge works fine, as does the thermostat. I didn't want to replace either!