305tpi warm idle hunting. IAC counts at zero
12-31-2016, 09:05 AM
#1
305tpi warm idle hunting. IAC counts at zero
Hi All
I know I know, this has been covered extensively on these boards but often the threads end without a success story. Have a 91 305tpi T5 that's stock apart from headers and exhaust (incl. cat delete) that hunts/ surges on idle.
Have an ALDL scan tool and from what I see it cannot achieve the desired RPM. Goes down to about 800rpm (desired is around 600 or so) and the IAC counts are at Zero and then it starts hunting. By then its in closed loop.
I had a look for vacuum leaks and sprayed carb cleaner around the bay; because of the hunting idle its difficult to tell if I've found a leak.
I suppose my question is that with the IAC counts at zero and the idle not settling to what the computer is trying to achieve, does that mean without doubt its vacuum leak? I read about people changing spark plug wires, ignition modules etc. but I'd guess the IAC at zero is a tell-tale that extra air is getting in?
The minimum air on the TB hasn't been messed with (still has the cover) and so I haven't touched that yet. On a mostly stock car, I'm guessing I don't need to?
help welcome
I know I know, this has been covered extensively on these boards but often the threads end without a success story. Have a 91 305tpi T5 that's stock apart from headers and exhaust (incl. cat delete) that hunts/ surges on idle.
Have an ALDL scan tool and from what I see it cannot achieve the desired RPM. Goes down to about 800rpm (desired is around 600 or so) and the IAC counts are at Zero and then it starts hunting. By then its in closed loop.
I had a look for vacuum leaks and sprayed carb cleaner around the bay; because of the hunting idle its difficult to tell if I've found a leak.
I suppose my question is that with the IAC counts at zero and the idle not settling to what the computer is trying to achieve, does that mean without doubt its vacuum leak? I read about people changing spark plug wires, ignition modules etc. but I'd guess the IAC at zero is a tell-tale that extra air is getting in?
The minimum air on the TB hasn't been messed with (still has the cover) and so I haven't touched that yet. On a mostly stock car, I'm guessing I don't need to?
help welcome
02-19-2017, 09:52 AM
#2
Re: 305tpi warm idle hunting. IAC counts at zero
Incase of any use to people with similar problems:
I managed to get the idle down (to the commanded level) by adjusting the minimum air screw (at the back of the throttle body above the throttle cable).
Along the way I cleaned the TB (which did have a fair amount of carbon), removed the IAC valve and cleaned it and the IAC passage in the TB. I checked function of the IAC valve by putting the car in diagnostic mode (paperclip in pins A-B of ALDL connector which serves to extend the IAC pintle); with it removed IAC passage and in a plastic bag as it will fall apart when it extends fully.
The TB minimum air screw was capped (suggesting it hadn't been messed with) and so I was hesitant to adjust it but with the scanner tool I was able to easily see the improvement it made to the idle and bringing the IAC counts up the desired 20 range at full warm idle.
oh, wasn't completely out of the woods as the noticed the throttle would stick. Not with the engine off but when running (could tell with the scanner tool as the TPS % would not go back to zero). Cleaned the built up gunk on the spring and shot some WD40 on it and some teflon lube. Similarly added some lube to the shaft running through the TB that the blades are connected to (where the shaft met the TB body). I also noticed the cruise cable was pretty tight so have, for now, loosened this at the cruise control module end.
Anyway, long post but I just wanted to provide some closure (lol) for anyone with a similar issue. Lots of good info on TGO and what I did is nothing new but didn't see many posts with a followup saying how they managed to deal with the issue.
Hopefully this is of some use
I managed to get the idle down (to the commanded level) by adjusting the minimum air screw (at the back of the throttle body above the throttle cable).
Along the way I cleaned the TB (which did have a fair amount of carbon), removed the IAC valve and cleaned it and the IAC passage in the TB. I checked function of the IAC valve by putting the car in diagnostic mode (paperclip in pins A-B of ALDL connector which serves to extend the IAC pintle); with it removed IAC passage and in a plastic bag as it will fall apart when it extends fully.
The TB minimum air screw was capped (suggesting it hadn't been messed with) and so I was hesitant to adjust it but with the scanner tool I was able to easily see the improvement it made to the idle and bringing the IAC counts up the desired 20 range at full warm idle.
oh, wasn't completely out of the woods as the noticed the throttle would stick. Not with the engine off but when running (could tell with the scanner tool as the TPS % would not go back to zero). Cleaned the built up gunk on the spring and shot some WD40 on it and some teflon lube. Similarly added some lube to the shaft running through the TB that the blades are connected to (where the shaft met the TB body). I also noticed the cruise cable was pretty tight so have, for now, loosened this at the cruise control module end.
Anyway, long post but I just wanted to provide some closure (lol) for anyone with a similar issue. Lots of good info on TGO and what I did is nothing new but didn't see many posts with a followup saying how they managed to deal with the issue.
Hopefully this is of some use
02-19-2017, 12:58 PM
#3
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Re: 305tpi warm idle hunting. IAC counts at zero
Good to hear the follow-up! Glad you're going again.