Am I missing a Thermactor/AIR Part? 94 351 High Idle.
#1
07-23-2017, 11:09 AM
Am I missing a Thermactor/AIR Part? 94 351 High Idle.
Posting a new thread for this since it got buried in another. I'll try to contain all relevant info in the first post.
Truck: 1994 F-250 XL
351 5-Speed Manual
No Cruise Control
8800 GVWR
There are no codes since I fixed the EGR. Never had, or currently have, codes for anything else
Background: Been struggling with a high idle issue since I bought the truck. 2 Theories: 1) Previous owner stupidity (IAC was unplugged, throttle stop screw messed with, crankcase vent in the drivers side valve cover was routed to the round plastic hole for the A.I.R system
) 2) General broken parts that you'd expect on a 94 with 192k miles.
Items Replaced:
- IAC - It was unplugged so I assumed it was bad. Could be right or wrong.
- TPS - Replacing this and tuning it in seemed to make a positive change. No more super-high idle surging.
- EGR Valve and Line (from manifold) - Line was broken. Seemed to make a positive change as well.
- Throttle cable, plastic piece was broken causing binding.
- Little ancillary things like the air filter (including the one for the crankcase vent), throttle body gasket, some questionable vacuum lines, etc.
Current situation:
Using yesterday as an example, this is very typical. Drive truck for 25 minutes. Should be warmed up. Park for a half hour. Restart, it's still fairly warm. Idle appears normal, see below:
Attachment 287728
Begin driving, come to a stop sign in 2 minutes and make a complete stop. Idle is around 1000RPM, see pic below. The next stop sign it could be a little higher (around 1100), a little lower (around 900), or still around 1000. It varies, but its high regardless.
Attachment 287729
The fact that it CAN idle normally, as shown in the first picture, leads me to believe it could be something electronic and/or related to the A.I.R/Thermactor system. As opposed to a bad intake gasket, worn throttle body shaft, or some other standard vacuum leak. Nor do I think it's something internal to the motor. It's extremely strong, no misfiring, no smoke, no oil use, and it runs super smooth especially right after a warm start.
Now the big question:
Here's something I just noticed today. One of the two A.I.R solenoids is not there, and there is a connector not plugged into anything. I think this is the TAD?
Could this be another previous owner hack? Or did the higher GVWR trucks only have one solenoid? If the TAD was there wouldn't it have a vacuum line? There are no disconnected vacuum lines.
Attachment 287730
If I understand the thermactor system correctly, it needs to "divert" air when at idle. If I'm missing the solenoid that does the diverting, then it's just giving the motor extra air at idle - thus high idle. Am I wrong?
Can someone tell me if I'm missing a part, and possibly point me to a part number? Does anyone have photos of a truck that's as close as possible in year/spec to this one, showing what it should look like (including vacuum line routing)? Any good vacuum diagrams for this year/spec?
I know this is tough since there are seemingly 10000 variations of these trucks
A few other pics, if they help. I can get additional pics if needed:
Truck: 1994 F-250 XL
351 5-Speed Manual
No Cruise Control
8800 GVWR
There are no codes since I fixed the EGR. Never had, or currently have, codes for anything else
Background: Been struggling with a high idle issue since I bought the truck. 2 Theories: 1) Previous owner stupidity (IAC was unplugged, throttle stop screw messed with, crankcase vent in the drivers side valve cover was routed to the round plastic hole for the A.I.R system
) 2) General broken parts that you'd expect on a 94 with 192k miles.Items Replaced:
- IAC - It was unplugged so I assumed it was bad. Could be right or wrong.
- TPS - Replacing this and tuning it in seemed to make a positive change. No more super-high idle surging.
- EGR Valve and Line (from manifold) - Line was broken. Seemed to make a positive change as well.
- Throttle cable, plastic piece was broken causing binding.
- Little ancillary things like the air filter (including the one for the crankcase vent), throttle body gasket, some questionable vacuum lines, etc.
Current situation:
Using yesterday as an example, this is very typical. Drive truck for 25 minutes. Should be warmed up. Park for a half hour. Restart, it's still fairly warm. Idle appears normal, see below:
Attachment 287728
Begin driving, come to a stop sign in 2 minutes and make a complete stop. Idle is around 1000RPM, see pic below. The next stop sign it could be a little higher (around 1100), a little lower (around 900), or still around 1000. It varies, but its high regardless.
Attachment 287729
The fact that it CAN idle normally, as shown in the first picture, leads me to believe it could be something electronic and/or related to the A.I.R/Thermactor system. As opposed to a bad intake gasket, worn throttle body shaft, or some other standard vacuum leak. Nor do I think it's something internal to the motor. It's extremely strong, no misfiring, no smoke, no oil use, and it runs super smooth especially right after a warm start.
Now the big question:
Here's something I just noticed today. One of the two A.I.R solenoids is not there, and there is a connector not plugged into anything. I think this is the TAD?
Could this be another previous owner hack? Or did the higher GVWR trucks only have one solenoid? If the TAD was there wouldn't it have a vacuum line? There are no disconnected vacuum lines.
Attachment 287730
If I understand the thermactor system correctly, it needs to "divert" air when at idle. If I'm missing the solenoid that does the diverting, then it's just giving the motor extra air at idle - thus high idle. Am I wrong?
Can someone tell me if I'm missing a part, and possibly point me to a part number? Does anyone have photos of a truck that's as close as possible in year/spec to this one, showing what it should look like (including vacuum line routing)? Any good vacuum diagrams for this year/spec?
I know this is tough since there are seemingly 10000 variations of these trucks
A few other pics, if they help. I can get additional pics if needed:
#2
07-23-2017, 07:27 PM
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#3
07-23-2017, 07:47 PM
Not necessarally, on HD trucks there was only 1 thermactor valve so only 1 control solenoid was needed.. that is the part next to the coil. If there aren't any open vacuum lines in that area then there was never a control solenoid there. This system injects air into the exhaust to help the cats burn off excess hydrocarbons so it is unlikely it is the source of your high idle problem.
#4
07-24-2017, 12:06 PM
Thanks for the replies. The fact that there are 2 different opinions just indicates how many damn variations there are on these trucks 
Understood the point about the vacuum lines, but due to the previous owner hackery I can't trust the presence (or absence) of disconnected vacuum lines as an indicator that something is missing. Could simply be mis-routed.
Does anyone else with an as-similar-as-possible truck also just have an empty electrical connector just floating around there?
Understood the point about the vacuum lines, but due to the previous owner hackery I can't trust the presence (or absence) of disconnected vacuum lines as an indicator that something is missing. Could simply be mis-routed.
Does anyone else with an as-similar-as-possible truck also just have an empty electrical connector just floating around there?
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