High Idle - IAC Valve
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High Idle - IAC Valve
Hello All,
I just replaced the TPS with the upgraded 'gold contacts' version with the hope of solving an off idle stumble when opening the throttle on a cold engine. To improve access to the TPS I removed the solenoid for the IAC. After reassembly I started the car and the idle speed was ~2000 RPM. I assumed it was the TPS - put the old one back, same high idle. So I focused on the IAC.
NOTE - I did not have an idle speed issue prior to swapping the TPS. Only the off idle stumble (came with the car).
A previous owner had replaced the IAC with p/n ABV0031 (Hitachi part), which is not listed as a part for the Scorpio. So I loosened the two Phillips head screws, started the car and found I could lower the idle speed by gently pulling the solenoid away from the valve assembly. This is when I discovered that the solenoid would 'pre-load' the valve assembly shaft when installed. This meant the valve assembly was 'leaking air' in its 'rest' state (no voltage applied to the solenoid). This struck me as strange. It may explain why the car would go into gear rather harshly - I expected the IAC to lower the idle speed slightly when moving from Park to Reverse or Drive. Maybe I was expecting too much from the early generation engine management systems.
I'm planning to replace the IAC with the correct Scorpio item (i.e. AC22). However, your feedback is appreciated as always.
I just replaced the TPS with the upgraded 'gold contacts' version with the hope of solving an off idle stumble when opening the throttle on a cold engine. To improve access to the TPS I removed the solenoid for the IAC. After reassembly I started the car and the idle speed was ~2000 RPM. I assumed it was the TPS - put the old one back, same high idle. So I focused on the IAC.
NOTE - I did not have an idle speed issue prior to swapping the TPS. Only the off idle stumble (came with the car).
A previous owner had replaced the IAC with p/n ABV0031 (Hitachi part), which is not listed as a part for the Scorpio. So I loosened the two Phillips head screws, started the car and found I could lower the idle speed by gently pulling the solenoid away from the valve assembly. This is when I discovered that the solenoid would 'pre-load' the valve assembly shaft when installed. This meant the valve assembly was 'leaking air' in its 'rest' state (no voltage applied to the solenoid). This struck me as strange. It may explain why the car would go into gear rather harshly - I expected the IAC to lower the idle speed slightly when moving from Park to Reverse or Drive. Maybe I was expecting too much from the early generation engine management systems.
I'm planning to replace the IAC with the correct Scorpio item (i.e. AC22). However, your feedback is appreciated as always.
Thank you and take care,
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
- andyofcolumbusmerkur
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Re: High Idle - IAC Valve
huh. Could you put a thin shim/spacer in there to fix the problem?
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Re: High Idle - IAC Valve
Original off-idle stumble on depressing accelerator is likely an EGR issue allowing some extra air into the intake.
High idle issue could be carbon deposits on IAC pintle and seat; or an error re soldering the new TPS pig tail to the harness (not sure how, but logic points to that action for diagnosis).
YMMV
High idle issue could be carbon deposits on IAC pintle and seat; or an error re soldering the new TPS pig tail to the harness (not sure how, but logic points to that action for diagnosis).
YMMV
Last edited by Ed Lijewski on Sat Feb 13, 2021 9:19 am, edited 1 time in total.
Descartes: "Cogito Ergo Sum"
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Re: High Idle - IAC Valve
Hello Andyofcolumbus,
Interesting workaround - a shim would be difficult but I could try a second O-ring. It would be worth experimenting with.
Hello Ed Lijewski,
The EGR was my original thought so I blocked all the vacuum lines except the feedback from the EGR to the transducer - no change. I won't be able to get back in the garage until Sun so I will clean the IAC pintle and seat plus check my soldering job. I did double check the wiring before solder but it can't hurt to check again.
If cleaning the pintle / seat and checking the wiring do not solve the issue I will experiment with a second O-ring. I don't see the latter as a solution but will confirm the basic testing I did today (Fri). In the meantime I'll order a new IAC from Rock Auto - I don't have a spare for testing so it will come in handy.
Interesting workaround - a shim would be difficult but I could try a second O-ring. It would be worth experimenting with.
Hello Ed Lijewski,
The EGR was my original thought so I blocked all the vacuum lines except the feedback from the EGR to the transducer - no change. I won't be able to get back in the garage until Sun so I will clean the IAC pintle and seat plus check my soldering job. I did double check the wiring before solder but it can't hurt to check again.
If cleaning the pintle / seat and checking the wiring do not solve the issue I will experiment with a second O-ring. I don't see the latter as a solution but will confirm the basic testing I did today (Fri). In the meantime I'll order a new IAC from Rock Auto - I don't have a spare for testing so it will come in handy.
Thank you and take care,
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
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Re: High Idle - IAC Valve
EGR is EEC controlled and doesn't actuate at/off idle. Disconnecting the EGR solenoid vaccum hose(s) has no effect under idle/low rpm conditions.
What's worth a (desperate...) try is to use a vaccum pump on the EGR nipple to work the diaphragm and pintle, while engine is cold and hot. Not more than ~15-20 lbs vaccum on the diaphragm.
Re the 2000 rpm high idle, for background do a search here. Your issue may be different, but you need to know what others have reported.
YMMV
What's worth a (desperate...) try is to use a vaccum pump on the EGR nipple to work the diaphragm and pintle, while engine is cold and hot. Not more than ~15-20 lbs vaccum on the diaphragm.
Re the 2000 rpm high idle, for background do a search here. Your issue may be different, but you need to know what others have reported.
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Lijewski: "Sum Ergo Drive-O. Mucho!
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Re: High Idle - IAC Valve
Forgot add above: did you install a new IAC gasket?
YMMV
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Lijewski: "Sum Ergo Drive-O. Mucho!
- brokencase
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Re: High Idle - IAC Valve
Replace with correct IAC. It should not "preload" and leak as you described.
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Re: High Idle - IAC Valve
Hello All,
Update Sun 14/02.
1. Checked the TPS wiring harness (I soldered in a new 'gold plated' Motorcraft TPS), and the colour coding was correct.
2. I did not replace the IAC gasket as during the TPS install I only removed the solenoid itself (O-ring only). However, after the idle issue I pulled the alloy casting to check movement of the valve in relation to the solenoid. The gasket was in very good condition and was not damaged in any way during disassembly. NOTE - the IAC is still the incorrect one (p/n ABV0031 installed by previous owner).
3. Next step is to replace the IAC with the proper one before proceeding with further testing. Unfortunately that will have to wait for a week until the part arrives.
I'll update this thread after the part has been installed and tested. Fingers crossed!
Update Sun 14/02.
1. Checked the TPS wiring harness (I soldered in a new 'gold plated' Motorcraft TPS), and the colour coding was correct.
2. I did not replace the IAC gasket as during the TPS install I only removed the solenoid itself (O-ring only). However, after the idle issue I pulled the alloy casting to check movement of the valve in relation to the solenoid. The gasket was in very good condition and was not damaged in any way during disassembly. NOTE - the IAC is still the incorrect one (p/n ABV0031 installed by previous owner).
3. Next step is to replace the IAC with the proper one before proceeding with further testing. Unfortunately that will have to wait for a week until the part arrives.
I'll update this thread after the part has been installed and tested. Fingers crossed!
Thank you and take care,
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
- brokencase
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Re: High Idle - IAC Valve
Sorry I just remembered the following...
I seem to recall that there was Tech Service Bulletin that talked about later Idle solenoids having a diode installed and that you need to verify that the polarity of the connection to the idle solenoid are correct.
Can anyone else attest to this? I'm looking through my TSB pdfs and I can't find it.
You should be able to test with a DMM your solenoid to determine if the diode is present or not.
Basically they added a diode later on to clamp the inductive spike of the coil de-energizing. As described here..
https://resources.altium.com/p/using-fl ... r-circuits
I seem to recall that there was Tech Service Bulletin that talked about later Idle solenoids having a diode installed and that you need to verify that the polarity of the connection to the idle solenoid are correct.
Can anyone else attest to this? I'm looking through my TSB pdfs and I can't find it.
You should be able to test with a DMM your solenoid to determine if the diode is present or not.
Basically they added a diode later on to clamp the inductive spike of the coil de-energizing. As described here..
https://resources.altium.com/p/using-fl ... r-circuits
Specialization is for Insects
- brokencase
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Re: High Idle - IAC Valve
Found it! What it came down to is some vehicles had the diode in the harness and they later migrated the diode to the solenoid.
Not sure if this is your issue but definitely worth mentioning.
Not sure if this is your issue but definitely worth mentioning.
Last edited by brokencase on Sun Feb 14, 2021 6:32 pm, edited 1 time in total.
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Re: High Idle - IAC Valve
...But the IAC harness connector is a one-way only plug, it can't be reversed.
YMMV
YMMV
Descartes: "Cogito Ergo Sum"
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- brokencase
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Re: High Idle - IAC Valve
Yes - but you may have to cut/swap the wires.
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Re: High Idle - IAC Valve
I wonder if a mismatched (P/Ns) IAC is involved in the Sudden High Idle Syndrome. The TSB doesn't mention sudden high idle, but the fly back issue makes sense as causing that.
YMMB
YMMB
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
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Re: High Idle - IAC Valve??
Hello All,
Recap; Car (~80K mi. / 125K km), has been running well other than a stumble coming off idle (i.e. accelerating away from a stop), until the engine has been running for a few minutes and occasionally difficulty starting when warmed up - throttle half open while turning the key is the workaround. Replaced plugs, wires, cap, rotor, fuel filter and air filter - ran much smoother but stumble still existed. I removed the solenoid only from the original IAC installed in the car (wrong part by the way), to make installing the new TPS (gold plated one), easier. Upon reassembly the car had a very high idle; ~2K RPM. Reinstalled the original TPS, no difference. Decided to order new IAC. No Check Engine Light (CEL), at any time.
=============================================================================================================================
Finally received my new IAC valve (Standard p/n AC22), shipment was delayed due to the snow storm in the US northeast.
Installed it today and guess what, same high idle (2K RPM). Difficult to start, have to hold throttle about half open for the car to start. No CEL at any time. Trouble shooting steps as follows;
1. Attached a vacuum gauge and the reading was ~16" at 2K RPM.
2. Because I had replaced all the vacuum hoses I disconnected them and plugged all the ports - same 2K RPM idle and ~16" of vacuum.
3. Unplugged the IAC while the engine was running - stalled immediately.
4. Reversed the IAC installation (electrical connector pointing towards the passenger fender) - no change.
5. Removed the IAC, covered the ports with duct tape and poked a ~4mm hole over the hole on the side intake - idle speed dropped to ~800 RPM, vacuum slightly better at ~17".
6. With the 'duct tape' IAC in place I reconnected the vacuum lines one at a time - same result as point 5 above.
This is the first time in over 50 years of tinkering with cars that I am truly stumped. I'm sure it is going to be something stupid. Hopefully someone can put me out of my misery.
Recap; Car (~80K mi. / 125K km), has been running well other than a stumble coming off idle (i.e. accelerating away from a stop), until the engine has been running for a few minutes and occasionally difficulty starting when warmed up - throttle half open while turning the key is the workaround. Replaced plugs, wires, cap, rotor, fuel filter and air filter - ran much smoother but stumble still existed. I removed the solenoid only from the original IAC installed in the car (wrong part by the way), to make installing the new TPS (gold plated one), easier. Upon reassembly the car had a very high idle; ~2K RPM. Reinstalled the original TPS, no difference. Decided to order new IAC. No Check Engine Light (CEL), at any time.
=============================================================================================================================
Finally received my new IAC valve (Standard p/n AC22), shipment was delayed due to the snow storm in the US northeast.
Installed it today and guess what, same high idle (2K RPM). Difficult to start, have to hold throttle about half open for the car to start. No CEL at any time. Trouble shooting steps as follows;
1. Attached a vacuum gauge and the reading was ~16" at 2K RPM.
2. Because I had replaced all the vacuum hoses I disconnected them and plugged all the ports - same 2K RPM idle and ~16" of vacuum.
3. Unplugged the IAC while the engine was running - stalled immediately.
4. Reversed the IAC installation (electrical connector pointing towards the passenger fender) - no change.
5. Removed the IAC, covered the ports with duct tape and poked a ~4mm hole over the hole on the side intake - idle speed dropped to ~800 RPM, vacuum slightly better at ~17".
6. With the 'duct tape' IAC in place I reconnected the vacuum lines one at a time - same result as point 5 above.
This is the first time in over 50 years of tinkering with cars that I am truly stumped. I'm sure it is going to be something stupid. Hopefully someone can put me out of my misery.
Thank you and take care,
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
Peter
1988 Merkur Scorpio, 1988 Plymouth Caravelle (police package), 1994 Volvo 940 Turbo Wagon, 2011 Hyundai Elantra GLS Touring
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Re: High Idle - IAC Valve
No one has found an answer to the intermittent Scorpio High Idle Syndrome (do a search here).
YMMV
YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!
Lijewski: "Sum Ergo Drive-O. Mucho!