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Well – it finally looks like my high-idle problem has been solved. As I mentioned in my last post, I was beginning to suspect that though the IAS opened-fully and closed-shut just fine, maybe the commutator was dirty/worn in the partially-open area that is important for fine-tuning idle speed. The last time I’d cleaned it, I tried opening it by prying open the 4 pairs of claws – but could feel something holding it back when I pulled, so I ended up just cleaning the valve-section. That cleanup was sufficient to allow the valve-window to open and close fairly easily at the time.
This time around I decided to pull it apart firmly, as I’d read posts that indicated the resistance was on account of the magnets. With that in mind, I was able to pull it apart quite easily. The commutator had tracks on it form the brushes (which were more like a contact-terminal on a spring) but was not very dirty – which was surprising since the motor is not completely isolated from the valve-area of the IAC. Considering the valve-end gets so dirty you would expect some of that dirt to make it’s way down to the commutator. Odd it was designed this way…
It’s SO much more easy to clean the IAC when it’s opened up. I think it’s also better as you can direct the cleaner at all of the valve-section without worrying about it travelling down to the motor (which it will). When I removed the cir-clip which holds the motor-armature to the shaft (and which it spins on), I noticed that the shaft had gummed-up oil on it that was probably on account of the cleaner mixing with the oil and drying it out. After cleaning it out, oiling the shaft, polishing the commutator with fine sand-paper, and flexing the contact-springs in a bit more towards the commutator - I was ready for the final step that was supposed to be the most problematic: inserting the armature back in without bending the contact-springs while fighting with the magnets. At the end of the shaft – on the commutator, there is a thick tapered plastic-washer that acts as a ramp for the contact-springs to get onto the commutator. This makes the task very easy. The trick is to hold the armature tight and steady while inserting it into the IAC body. Was anti-climatic for me actually, because it worked first shot. Took about 10 secs to fit it in.
One VERY important thing to remember when re-assembling the IAC, is that there are two ways to position the valve-end (the section with the valve that is attached to the armature) into the IAC body. These 2 positions are 180 degrees apart. The correct way will allow each contact (there are 3) to only track on one commutator-section over it’s complete 60 degree swing (the commutator is broken up into 3 copper-wedges – each with it’s own contact brush). The wrong way would allow each contact to cover 2 commutator sections during it’s 60 degree travel which would confuse the heck out of the ECU and of course, play havoc with your idle. More seriously, at one point in it’s travel – the 3 contacts would bridge all 3 commutator sections causing a total short in the IAC that would most likely fry the ECU transistors. So – make sure you mark the 2 sections before opening it up or check the armature orientation w.r.t the contacts before installing.
SO – after installing the fully-serviced IAC I took one additional step before starting the engine: I unplugged the computer, and left it unpowered for an hour. I could have also disconnected a battery terminal, but the ECU was easier for me as I had the cover off. I did this after reading Abe Crombie’s post on ECU ‘memory’ (see link below).
http://brickboard.com/ARCHIVES/1998JUN/10001844.shtml
Granted mine is an 85-era ECU and he’s referring to a much-more recent one, but what the heck. I didn’t have anything to lose (I’d actually unplugged the ECU before fitting the IAC in so I didn’t even have to wait).
After starting her up the idle immediately rose to around 1500 and then settled to a nice 700. The black idle-bypass screw was all the way in (since my butterfly-valve doesn’t completely seal the TB and lets in a tiny-amount of air I thought I’d avoid the bypass when trying it). So did this powering-down of the ECU help reset any memory it may have had of settings resulting from previously clogged TB, IAC, injectors etc ? Dont know - but it's something I'll do after every major cleanup in the future.
I still have a problem where grounding the Base-Idle test point does not affect engine speed at all to allow me to adjust the Idle-Bypass screw. But I could get around that by closing the IAC manually while I use the bypass-screw (right ?)
Hope my idle stays low now. I’m thankful that my ECU seems to function fine, and most of all – thankful to all you helpful folks out there !
Next mini-project is setting the CO level. My current test LED-light on the CO point is always on. AMM resistance is about 380 ohms which I believe is correct. Will try setting this using my spare AMM and see if I can get it to blink. Anyone else have a problem setting their CO where the test LEDs never really blink ?
Thanks everyone !
Noel
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