Coil and bosch sensor fitted, to no effect. Worth doing anyway though as I am slowly renewing the lot of it.

I've been dwelling on one thought- maybe someone with a better understanding of these ECUs can offer an opinion.

- Renewed IAC doesnt function
- Rev hang in P, N when revved from idle that slowly drops
- Occasional noticable rev hunting, hard to pinpoint exa t conditions
- Heavy fuel con. obviously
- Auto downshifting lurch just before coming to a stop

This leads me to suspect that I could have a bad throttle position sensor that is giving readings resulting in a rich condition and failing to give a signal that indicates a closed throttle position- hence the IAC and downshifting.

I have spare and spotless throttlebody and a younger TPS (condition unknown) to trial some time this week. Nevertheless I am interested to know A: does the idle circuit relay on TPS in this way? B: will a faulty TPS throw the shift (up AND down) significantly out?

Still enjoying the hunt. So close I can smell it! Smells like petrol

Andrew.

Have you checked for VAC leaks yet?

Wherever I can I have inspected hoses and fittings, theyre all pretty tight and have no visible cracks anywhere. but it'll be a while before I can get to the fittings behind the dash. I went over all the engine bay vac lines I could when I swapped the coil.

Couldnt hear anything from the brake booster shaft behind the pedal.

Still have to go crazy with some carby cleaner- but i assume this only really useful at the manifold right? At this point I cant afford vacuum pressure testing gear and I'm not too savvy with smoke testing..

Either way I will probably change the TB anyway. I havent had a chance to shine a torch into the manifold header yet to see how much is built up, when i pulled the airtemp sensor out it was like a sump plug, haha!

Andrew.

A) Yes

B) Yes

Thanks for the answers SWC.

As well as checking the Vac again with more carby cleaner I'll see what happens if i suss out the TPS. I'd call it an easy afternoons work anyway so its eell worth it.

I just remembered i havent looked at the heater tap closely yet. Could be worth checking interior duct controls as well as i dont really use the AC, ever.

Cheers, A.

Had some fun with carby cleaner today. Couldnt get any changes out of the idle quality, but its still behaving like there is a leak somewhere. A bit of shuddering and the occasional sudden drop.

I also changed to a spare throttlebody i had that was spotless with the position sensor that came with it. No evident changes, did the learn idle and throttle procedures and it was idling like rubbish afterwards so i screwed the adjusting screw back in and redid the throttle procedure. As it is now in Park/drive it still idles at 600/200 respectively.. at least, as indicated by the tach.

One interesting thing I found was the idle control solenoid I fitted a while back was still pretty damn clean inside. In fact it looked fairly new to be honest. That definitely makes me think that the idle control isnt operating at all..

I think I will need to have a good look at the idle control circuit and maybe see if the ECU is failing to give a signal. I had always assumed that ECUs dont usually fail though.. if it is screwing that up- maybe fuel trims too?

At this point, I am more tempted to find a workshop in sydney that is good with fault diagnosis and electrical work to deal with both my problems. Any suggestions there?

cheers, A.

Thought i might try and find an ecu to test before I give it to a mechanic. I had a quick search, but didnt find info on it.

i assume if I do get an XG or ED auto ecu it will be a matter of remove negative bat terminal, unplug and then plug in new one. If its the same catch code it should be smartlock compatible and should work fine once connected.

Is that right? Or will I run into smartlock module dramas if it doesnt recognise the one unique computer? That little red box still scared me!

A.

I know you said that you've checked all the vacuum hoses, but have you by any chance inspected the hose that runs from the map sensor to the intake manifold?

Its a pain in the a** to inspect properly, but mine had similar symptoms to yours and it was by chance that when I unplugged this hose from the map sensor there was no change to idle.

This made me jump under the car and look at the connection of the hose onto the intake manifold to discover it had a hairline crack in it.

Best of luck anyway!

For the Au at least (nfi on yours) you set the base idle speed with the idle adjust screw with the idle air unplugged.
You set it to 700 RPM (when the engine is super hot) then plug the IAC valve back in and it jumps up to 900 RPM idle.

I wonder if something similar would help you diagnose your IAC potentially, IE have the engine idle then pull the plug on the IAC, see if it changes.
Otherwise it'd probably be a scope job see if its getting power.

200RPM idle in drive sounds *super* low to me is that in spec for your engine?

No way! At startup it doesnt drop too much but once she gets warm it drops radically with T.C. load introduced, plus steering and electrical load etc. The problem I've found is if you dial the idle speed up into a better range without the solenoid working then the park or neutral idle ends up high enough to be over stall speed. Not really a good idea I think haha.

I have a replacement 3DDC Xg ecu to trial now