Coolant temp sensor and ISC/IAC Operation

JMO · 29-04-2009, 10:22 PM

In trying to find the cause for my rough idle, I've worked my way through a looooong list of possible causes. I came across a thread on here that went a little bit into how the ISC operates and it mentioned that it relies on information detected by other various sensors.

The one that I am currently interested in is the coolant temperature sensor as, from what I can gather, helps to adjust the fuel flow, spray pattern etc. The reason it is of interest is that a fair while ago (just before my troubles started...I think?) I flushed the coolant system with washing soda and it did a fantastic job. I did however do a few fills with the stuff in there and I'm guessing I didn't flush it all out as it caused the aluminium radiator to leak a few days later.

I'm hoping (yes hoping :P) that the coolant temp sensor is also made of aluminium and has been attacked by the residue that was left over. To date I still find a slight buildup after I've removed and refitted the hoses for one reason or another and haven't tightened them enough.

So, can someone tell me if the coolant temp sensor is sitting in coolant, causing it to drain if it is removed? If so I'll wait until the next coolant flush before checking.

Also, what other sensors does the ISC rely on for info and whereabouts are they? (I know the A/C is one, but can't seem to find it.)

I did think that it might have been a mount issue, but after sitting and listening to what is going on I think I may be on the right track. A pulsing (starts strong and then fades, felt mostly in D and R but ever so slightly in P,N) every 5 or so seconds as the ECU recalculates? and every so often (rare occassion) the revs drop enough (400-500) to make you think the engine is about to stall (perhaps due to slight flooding of fuel or perhaps not enough air) then kicks into life again.

Sorry for the long post but again, can someone tell me if the coolant temp sensor is sitting in coolant, causing it to drain if it is removed? If so I'll wait until the next coolant flush before checking. Hopefully it isn't torqued to much because I'll most likely have to use a ring spanner to get at it.

Thanks

Foggy · 30-04-2009, 01:16 PM

Im pretty sure the only temp sensor in an AU is the 1 mounted in the back off the head and it doesnt go into the water jacket.

JMO · 30-04-2009, 01:30 PM

That's the one I was referring to. I pulled it out. It is made of copper/brass so no go on the aluminum idea. Would a build up of crud around the area it is measuring the temperature from cause any problems or am I clutching at straws?

I'm almost certain the symptoms I described only happened after I did the flush. Would a build up of crud in the cooling system cause anything like I mentioned? The car drives fine, it's only once it drops to about 600rpm that you can feel anything.

If not this sensor, any ideas on others that effect the fuel flow/spray pattern or ISC?