[philcrombie]

Having finally started my '96 Aero after 3months non-use and a great pile of new parts for my GT3071r build - started on the button but idle isnt happy.

Starts fine, but immeditately idles too high from cold.

Pinch the IAC hose going to intake after throttle body (on the top) and the revs drop to normalish. Let go and the idle stays at 1k.... Might drift again.

Take car for a drive for 15mins and get it hot.

At idle Engine now cycling between 1500 and 2000 rpm every second. Then it will suddenly cut to 3k and hold it steady. Again squeezing the IAC hose drops the revs but they go straight back up again and it's really fighting it when you squeeze it.

I gave the IAC a really good clean during the rebuild but it hasnt been run for 3months so could have expired....

Could this be something completely different though? There's what I think is the brake booster hose on the back of the manifold. This used to pop off and gave very similar. It's OK this time.

Just to add: engine is smoothy smooth. No misfires or grumbles. (just to cover that potential)

Phil

 

[mark e]

Dodgy connection to or failed throttle position sensor?

Could also be a sticky AIC valve. If you have access to a bench power supply, applying a variable voltagel between about 4 and 12V will see the valve rotate. If it doesn't, it's still gunked up.

 

[Ryan_W]

Potential air leak on the inlet side of things?

I had a massive 'hunting' issue on my old CR-X. I'd changed the inlet manifold gasket, TB gasket, adjusted the Fast Idle Thermal Valve, the Idle Air Control Valve, PCV valve and played around lots. Ended up being the TPS being out.... I hate stupid idling! lol.....

 

[philcrombie]

Thanks Gents!

This intake manifold side of the car wasnt really touched so I have only done:

1) Took the IAC off to clean it about 2 months ago. Will check connection on the back ok and maybe take it out to test it - didnt know it's rating - tks mark. I might buy a spare too - At least I'll have a comparison part.

2) Had throttle delivery pipe take off throttle body - shouldnt affect idle. To me , this must either be a sensor OR air getting in after the throttle body. In theory I could draw air straight into throttle body with nothing in front and it should still idle.

3) TPS connector has been off too... this is one I didnt think would have this impact but I'll reseat it a few times to be sure it's connecting ok.

Hopefully will get a look tonight although I've overcooked my car antics of late!

 

[Ryan_W]

My monies on the TPS voltage being off... Remember to test on a closed and open throttle.

Since I know sod all about Saabs, I can't give you the correct figure off the top of my head, nor can I find one via google....

On a b16 (Honda engine) it should read 0.4-0.5v closed and 4-5v open throttle haha

 

[philcrombie]

Just update: AIC was sticking so I cleaned it again (even though it hasnt been driven since last clean!)

I put 12v across it and it flicked back and forth nicely. Started car and idle was 100% perfect so proof that issue is close to AIC

Once hot, it started cycling again 1500-2000. Returning throttle to idle whilst moving is jerky / harsh after a delay.

Key point: I nipped the AIC to manifold pipe whilst it cycled to dip the revs. Let go and they stayed down at 800 odd. This means there are no other leaks and the AIC is still not happy.

Either - there is something that keeps coming out inside to stick the AIC - or even when clean it is misbehaving / worn out. Thinking back - it always had it's little moments and needed cleaned more often than should be required (and it was never that dirty).

Maybe it's got 'weak' - I've ordered another 2nd hand. New I can get for £90 but I'm skint!

 

[mark e]

I used to have a very troublesome one- I think sometimes they get clogged on the shaft such that a squirt of carb cleaner isn't good enough to shift it. I actually ended up applying a 6hz AC signal to it whilst immersed in a bath of engine oil for several hours to free the shaft from all muck. That was more effective.

 

[philcrombie]

Sounds like this one tbh. I like your bath idea! ha. Can't believe I've done all this work only to have the AIC being the biggest setback... could be worse I guess....

Maybe I'll get a super fresh one from M5 saabcentre.... you never know.