High Idle Puzzle
Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 208
Likes: 1
From: Oregon
High Idle Puzzle
HI FTE,
1989 V8 302 5.0 engine here
I have a high idle. the engine starts high to warm up and then stays high. right when it starts to get warm sometimes it would slow down for a bit to a point where the engine almost dies for a quick second, then it ramps it right back up and keeps it high. this is about 5 min after the turn of the key. Idle speed on flat ground is around 20mph.
Normally on my friends truck, when you separate the connection plugs for the air bypass valve, the engine speed slows way down. On this engine when i pull the plug on the air by pass valve during the engine running, nothing changes and the idle speed doesnt drop.
I have adjusted the idle screw down, nothing changed. i used a throttle body cleaner on the inside, nothing changed. i replaced the o2 sensor, nothing changed. i had replaced the idle air bypass valve, nothing changed. i dont know what to do next. any help is appreciated
thanks
matt
1989 V8 302 5.0 engine here
I have a high idle. the engine starts high to warm up and then stays high. right when it starts to get warm sometimes it would slow down for a bit to a point where the engine almost dies for a quick second, then it ramps it right back up and keeps it high. this is about 5 min after the turn of the key. Idle speed on flat ground is around 20mph.
Normally on my friends truck, when you separate the connection plugs for the air bypass valve, the engine speed slows way down. On this engine when i pull the plug on the air by pass valve during the engine running, nothing changes and the idle speed doesnt drop.
I have adjusted the idle screw down, nothing changed. i used a throttle body cleaner on the inside, nothing changed. i replaced the o2 sensor, nothing changed. i had replaced the idle air bypass valve, nothing changed. i dont know what to do next. any help is appreciated
thanks
matt
Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 363
From: Candy Mountain
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
HI FTE,
1989 V8 302 5.0 engine here
I have a high idle. the engine starts high to warm up and then stays high. right when it starts to get warm sometimes it would slow down for a bit to a point where the engine almost dies for a quick second, then it ramps it right back up and keeps it high. this is about 5 min after the turn of the key. Idle speed on flat ground is around 20mph.
Normally on my friends truck, when you separate the connection plugs for the air bypass valve, the engine speed slows way down. On this engine when i pull the plug on the air by pass valve during the engine running, nothing changes and the idle speed doesnt drop.
I have adjusted the idle screw down, nothing changed. i used a throttle body cleaner on the inside, nothing changed. i replaced the o2 sensor, nothing changed. i had replaced the idle air bypass valve, nothing changed. i dont know what to do next. any help is appreciated
thanks
matt
1989 V8 302 5.0 engine here
I have a high idle. the engine starts high to warm up and then stays high. right when it starts to get warm sometimes it would slow down for a bit to a point where the engine almost dies for a quick second, then it ramps it right back up and keeps it high. this is about 5 min after the turn of the key. Idle speed on flat ground is around 20mph.
Normally on my friends truck, when you separate the connection plugs for the air bypass valve, the engine speed slows way down. On this engine when i pull the plug on the air by pass valve during the engine running, nothing changes and the idle speed doesnt drop.
I have adjusted the idle screw down, nothing changed. i used a throttle body cleaner on the inside, nothing changed. i replaced the o2 sensor, nothing changed. i had replaced the idle air bypass valve, nothing changed. i dont know what to do next. any help is appreciated
thanks
matt
Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 363
From: Candy Mountain
You won't be able to reset the stop screw properly until all the vacuum leaks have been addressed.
Pulling codes is a good idea, but don't start replacing parts because of codes. A simple survey for mechanical problems including tune up parts, ignition timing, vacuum leaks, etc. will be a good place to start.
All that said, pulling power off the IAC with no change in idle is a dead give away for vacuum leaks.
Pulling codes is a good idea, but don't start replacing parts because of codes. A simple survey for mechanical problems including tune up parts, ignition timing, vacuum leaks, etc. will be a good place to start.
All that said, pulling power off the IAC with no change in idle is a dead give away for vacuum leaks.
Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 208
Likes: 1
From: Oregon
Matt, return the Idle screw back to where it was if it is marked like most are. That screw is not for idle adjustment and is factory set. If it is set wrong it can mess up your diagnostic process. Many discussions about it. You should check your diagnostic codes to try and isolate the problem area. I am including a video in case you are unfamiliar with the process. You can use a paper clip instead of the jumper wire he uses. Let us know what codes you get and get the truck to operating temp before testing. Just do the KOEO test first. Also you should follow the advice above and check all vacuum lines first. Sandy
Thanks for the input.
While driving the engine would throw a code briefly when driving. If you weren't looking, you would miss it and it wouldn't stay on. So I decided to pull the OBD1 codes from the van by using the jump wire technique.
I got codes:
21: engine coolant temp "ECT" out of self-test range
24: air change temp "ACT" out of self-test range
32: EGR sensor below the closed limit.
these are the codes i have got before. i dont drive it much. so they should be the same as i havent changed really anything during this time gap.
I have posted about this before. here is the link https://www.ford-trucks.com/forums/1...ors-oh-my.html
Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 208
Likes: 1
From: Oregon
Matt
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Hi Sandymane,
Thanks for the input.
While driving the engine would throw a code briefly when driving. If you weren't looking, you would miss it and it wouldn't stay on. So I decided to pull the OBD1 codes from the van by using the jump wire technique.
I got codes:
21: engine coolant temp "ECT" out of self-test range
24: air change temp "ACT" out of self-test range
32: EGR sensor below the closed limit.
these are the codes i have got before. i dont drive it much. so they should be the same as i havent changed really anything during this time gap.
I have posted about this before. here is the link https://www.ford-trucks.com/forums/1...ors-oh-my.html
Thanks for the input.
While driving the engine would throw a code briefly when driving. If you weren't looking, you would miss it and it wouldn't stay on. So I decided to pull the OBD1 codes from the van by using the jump wire technique.
I got codes:
21: engine coolant temp "ECT" out of self-test range
24: air change temp "ACT" out of self-test range
32: EGR sensor below the closed limit.
these are the codes i have got before. i dont drive it much. so they should be the same as i havent changed really anything during this time gap.
I have posted about this before. here is the link https://www.ford-trucks.com/forums/1...ors-oh-my.html
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Your code 21 and 24 could also have been triggered if your truck was not up to operating temp when you did your test. If you ran the codes with a cold engine, It would be good if you did it again at temp.
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Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 208
Likes: 1
From: Oregon
Matt
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
the truck was not at operating temp when checked. Thanks for the help. I was having some trouble with these codes before. now i think ill try to trace my vacuum line and check for the leaks with a cigar or the car cleaner and replace the lines needed. would it be a good idea to start around the egr sensor? since thats the code that popped up?
Matt
Matt
Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 208
Likes: 1
From: Oregon
you think that would cause it to turn the check engine light on only a flash here and there during riving conditions? Thats what im seeing as mentioned in the linked post above
Elder User
Joined: Sep 2012
Posts: 505
Likes: 7
Yes, if the EGR position sensor doesn't see the correct position. My CEL flashed intermittently when the electrical connector to the vacuum solenoid was rattling loose in my truck. What I'm getting at is EGR doesn't have to set a constant CEL, it can be interimittent.