How can I test my LH ISV control circuit?
07-01-2018 | 01:35 PM
#31
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Joined: May 2014
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From: South Florida
I am pretty sure the two I got from Roger are "Loewe," and are made in Germany. If Roger supplies them, then I have confidence they have been working for him. That being said, something is causing this!
Two thoughts since I had problems with my ISV on my 86.5
1) The ISV is basically a motor of sorts with two sets of windings with a common ground. Give it voltage one way, and it rotates that way. Give it voltage the other way and it goes the other way. The problem in my case wasn't that it would move it was that it would move very jerkily in one direction when I tested it with a bit of load (my finger in the end) and low voltage (from my bench power supply).
Everyone should have a nice variable current limited bench power supply. When I tore the unit apart I found that one of the brushes had worn down a lot, and the commutator bar was going bad. That would cause the unit to stutter in one direction, the other was fine.
2) Cheap ISV's on Ebay are 14k garbage. I bought one and it turned out not to fit the plug on the car because the metal frame was so badly made. When I ripped it apart it was junk in construction compared to the original Bosch one. So I bought a genuine Bosch, and the car has been happy ever since.
1) The ISV is basically a motor of sorts with two sets of windings with a common ground. Give it voltage one way, and it rotates that way. Give it voltage the other way and it goes the other way. The problem in my case wasn't that it would move it was that it would move very jerkily in one direction when I tested it with a bit of load (my finger in the end) and low voltage (from my bench power supply).
Everyone should have a nice variable current limited bench power supply. When I tore the unit apart I found that one of the brushes had worn down a lot, and the commutator bar was going bad. That would cause the unit to stutter in one direction, the other was fine.
2) Cheap ISV's on Ebay are 14k garbage. I bought one and it turned out not to fit the plug on the car because the metal frame was so badly made. When I ripped it apart it was junk in construction compared to the original Bosch one. So I bought a genuine Bosch, and the car has been happy ever since.
07-08-2018 | 11:21 PM
#32
Thread Starter
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Joined: May 2014
Posts: 3,489
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From: South Florida
OK, so a minor update. I bought a cheap Ebay ISV to see if it makes any sort of difference. I noticed the valve can be easily moved by hand, as noted above (my original one is frozen shut, and the second one that contributed the the crazy high idle is frozen wide open). I measured the resistance across the two coils, and they were in the ballpark as described above. I did Greg's test, where I just plugged it in electrically and started the car, and I could see that the LH is controlling it. It resisted manual movement this way, and I could see it change when I revved the motor, turned on the AC, etc. So I swapped this with the one I had on there. Tbh it didn't make a huge difference. General behavior is still roughly the same, although idle seems to be about 100 RPM lower, so I guess that's good. But the one I took off also measures fine electrically, and the valve itself is not frozen in position. I'll keep it, especially since the Ebay valve may not last long. Fortunately, I've become rather adept at swapping these things while only removing the air box and MAF to get to it. A 6mm ratcheting gear wrench is key here, at least for the clamps I have on the ISV hoses, as is making sure you have the screws on those clamps clocked such that you can get to them.
Now that I've verified the LH is doing it's thing, and the ISV is generally working as it should, I will revisit the idle screw setting procedure. I don't expect that to fix anything, although it may lower idle a bit. I think I should take another look at the exhaust vapor recovery stuff, to make sure none of those valves are leaking. I checked them when I was having the 2K+ idle issue and they had no noticeable effect, but given the frozen open ISV at that time, I don't know that I would have noticed a small leak. Worth another look.
Now that I've verified the LH is doing it's thing, and the ISV is generally working as it should, I will revisit the idle screw setting procedure. I don't expect that to fix anything, although it may lower idle a bit. I think I should take another look at the exhaust vapor recovery stuff, to make sure none of those valves are leaking. I checked them when I was having the 2K+ idle issue and they had no noticeable effect, but given the frozen open ISV at that time, I don't know that I would have noticed a small leak. Worth another look.