Gary Lewis Posted September 14, 2017 Share Posted September 14, 2017 Basically, it's a LED test light that lights up green for ground (hooked to battery +) and red for power (hooked to battery -). Any other body ground lights up nice and bright green, while this IAC ground is very dim. At least it was after that long drive. The IAC is probably pulsed, so the ground is going on and off. And your test light thingee is pulsing, but so fast you can't see the pulses. Link to comment Share on other sites More sharing options...
mp470 Posted September 14, 2017 Author Share Posted September 14, 2017 The IAC is probably pulsed, so the ground is going on and off. And your test light thingee is pulsing, but so fast you can't see the pulses. Was KOEO as I've got nothing to backprobe it with at the moment without damaging the connector. Link to comment Share on other sites More sharing options...
myrl883 Posted March 6, 2018 Share Posted March 6, 2018 Was KOEO as I've got nothing to backprobe it with at the moment without damaging the connector. My '86 302 does exactly the same thing. I've been thinking IAC, but don't really know how to test one. My guess is that they get sticky with age and the goo buildup that seems to happen with them. Is the problem usually electrical, or the valve itself? If it makes a difference, my truck has been sitting the better part of the last 8 years. It's only accumulated about 6000 miles during that time. Link to comment Share on other sites More sharing options...
mp470 Posted March 6, 2018 Author Share Posted March 6, 2018 My '86 302 does exactly the same thing. I've been thinking IAC, but don't really know how to test one. My guess is that they get sticky with age and the goo buildup that seems to happen with them. Is the problem usually electrical, or the valve itself? If it makes a difference, my truck has been sitting the better part of the last 8 years. It's only accumulated about 6000 miles during that time. I thought it was the IAC too and I fired the parts cannon at it (replaced without testing - mechnical anyway - basic electrical OK, ie power and ground), but it was not to be. I cleaned the existing IAC extensively before replacing. Also sat for long periods as best as I know its history. I've had it parked for our 6 months of winter so soon it will be back to the drawing board. Link to comment Share on other sites More sharing options...
mp470 Posted April 22, 2018 Author Share Posted April 22, 2018 My '86 302 does exactly the same thing. I've been thinking IAC, but don't really know how to test one. My guess is that they get sticky with age and the goo buildup that seems to happen with them. Is the problem usually electrical, or the valve itself? If it makes a difference, my truck has been sitting the better part of the last 8 years. It's only accumulated about 6000 miles during that time. If you're still around, I just resolved it by adjusting the idle screw. I was trying to do a KOER test and it would stall out. However even after the stall and the engine type output, out came code 12 for idle RPM too high - tipped me off. Link to comment Share on other sites More sharing options...
vjsimone Posted April 25, 2018 Share Posted April 25, 2018 If you're still around, I just resolved it by adjusting the idle screw. I was trying to do a KOER test and it would stall out. However even after the stall and the engine type output, out came code 12 for idle RPM too high - tipped me off. Just FYI - It is not the Idle Screw, it is the Throttle Valve Stop Screw. The computer controls the Idle. Adjusting this screw changes the electrical characteristics of the TPS. The Stop screw adjustment is to keep the valves from sticking to the Throttle Body due to the engine vacuum. Basically, it is adjusted at the factory barely against the Stop Arm connected to the throttle plate rod. This screw should never be adjusted from the factory, unfortunately old school lads attempt to adjust an Idle by turning this screw in and out. Link to comment Share on other sites More sharing options...
mp470 Posted April 25, 2018 Author Share Posted April 25, 2018 Just FYI - It is not the Idle Screw, it is the Throttle Valve Stop Screw. The computer controls the Idle. Adjusting this screw changes the electrical characteristics of the TPS. The Stop screw adjustment is to keep the valves from sticking to the Throttle Body due to the engine vacuum. Basically, it is adjusted at the factory barely against the Stop Arm connected to the throttle plate rod. This screw should never be adjusted from the factory, unfortunately old school lads attempt to adjust an Idle by turning this screw in and out. Thanks for the insights. I'm not sure what was done to it before I got it, but I'm slowly learning its quirks thanks to this forum. Link to comment Share on other sites More sharing options...
85lebaront2 Posted April 25, 2018 Share Posted April 25, 2018 Just FYI - It is not the Idle Screw, it is the Throttle Valve Stop Screw. The computer controls the Idle. Adjusting this screw changes the electrical characteristics of the TPS. The Stop screw adjustment is to keep the valves from sticking to the Throttle Body due to the engine vacuum. Basically, it is adjusted at the factory barely against the Stop Arm connected to the throttle plate rod. This screw should never be adjusted from the factory, unfortunately old school lads attempt to adjust an Idle by turning this screw in and out. Vinny, if it is a 1985.5 or 1986 the screw is adjusted for as close to 1.0 volts at closed throttle as possible, much more and it starts trying to open the EGR valve. Link to comment Share on other sites More sharing options...
vjsimone Posted April 25, 2018 Share Posted April 25, 2018 Vinny, if it is a 1985.5 or 1986 the screw is adjusted for as close to 1.0 volts at closed throttle as possible, much more and it starts trying to open the EGR valve. I don't believe the intent was to use that screw to adjust the TPS voltage, although you can. The early TPS had a slotted hole to adjust the TPS voltage. Link to comment Share on other sites More sharing options...
vjsimone Posted April 25, 2018 Share Posted April 25, 2018 I don't believe the intent was to use that screw to adjust the TPS voltage, although you can. The early TPS had a slotted hole to adjust the TPS voltage. This procedure can be used to fix a maladjusted Throttle Stop Screw. But I would first back the screw out so that it is not putting pressure on the Stop Arm. Then adjust the screw inward so that it just makes contact, slight pressure with the Stop Arm. This takes it back to close to the factory adjustment. Then I would measure the voltage output of the TPS, adjust the TPS (if adjustable) to 0.6 to 0.9 V. closed throttle. New TPSs don’t have the slots for adjustment, you can add slots by drilling/reaming the existing holes. Check the idle rpm, If the idle is not as specified, I would try this procedure; http://www.garysgaragemahal.com/efi-idle-speed-adjustment.html Page F168 Re-check TPS voltage. You may have to adjust this prosses a bit. I have used it and have been successful, others have as well, and some have not. Link to comment Share on other sites More sharing options...
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