Over revving 1998 1.8i XU7JB

[SIIVION]

Good day.

At my whits end...

3 weeks ago I went to start my car, it revved extremely high, tried it a few times and exactly the same thing. Had a look at engine and found the air box bolted underneath the throttle housing was cracked. Taped it, didn't work, glued it didn't work and finally fibre glassed it which did work so no air leak there now. I did scour the internet for another box but impossible to buy , comes with the complete manifold.
All was ok for a day or so.

Every time I drive after about 20 mins the revs become erratic, particularly when clutching they go wild.
I have changed the throttle position sensor, the idle sensor.
I had it checked with a diagnostic machine resulting in no fault codes.

I have a coolant temperature sensor to fit now but do not know where it is!! I really don't want to interfere with other sensors just in case I muck them up.
Went to Wilco to buy the Haynes but it does not cover the 1.8i engine!

Does anybody know where the coolant temp sensor is located please?

Also, is it a likely cure?

[Johny555]

Maybe idle control valve,had the same with my old vectra years ago,at idle it was up down,up down,

[SIIVION]

Hi. Thanks. I said it was the idle sensor but It was the Idle control valve I changed so it's not that.

I am only attempting to change the coolant temperature sensor as it seems to happen when it has warmed up.

[Pdamo]

Hi will dig it out for you

[Col]

I would be looking at the previuosly repaired plenum personally.

[SIIVION]

thankyou. i will triple check it in the morning but do believe it is airtight

[Pdamo]

just out of interest did you remove and clean out the full emission system .If it has been drawing air then I would thing it could be well clogged up with Oily gunk. Just did my brothers and ended up taking the whole thing off Cleaning it with Gunk and jet washing it was full of Crud

[SIIVION]

Col: Thankyou, I did check the plenum(box) and it still had two 1mm air leaks, now with another layer of fibreglass the engine is running smoothly.
Pdamo: Not necessary now, thanks anyway

A number of lessons learnt.
Each time I had 'repaired' the plenum after a short use on the vehicle it would have the same problem, I had previously not known the importance of it being absolutely airtight, two 1mm holes made the difference.
I certainly went too far in the wrong direction by changing parts unnecessarily.

Still searching the web for a new box :-)