Idling issues
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Mountain Pass
Joined: Jul 2020
Posts: 153
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Idling issues
Hello, I’m having idling it is on my 1986 302 EFI Ford truck. symptoms:
On start up from cold it idles high at up to 2000 RPMs. After one minute it drops to about 1200 or so RPMs.
When I put it in gear the RPMs surge and it moves vehicle forward without giving it any gas.
Driving around it idles somewhat normal but still high.
When I put it in park the RPM surge again. High RPMs in park.
I have thoroughly cleaned the IAC and IAC solenoid plunger. I have thoroughly cleaned out the throttlebody. I have replaced the TPS.
Also, when I disconnect the IAC while it’s running it’s still idles exactly the same with no change.
Can you please give me some troubleshooting steps to continue trying to identify this problem? Thank you
On start up from cold it idles high at up to 2000 RPMs. After one minute it drops to about 1200 or so RPMs.
When I put it in gear the RPMs surge and it moves vehicle forward without giving it any gas.
Driving around it idles somewhat normal but still high.
When I put it in park the RPM surge again. High RPMs in park.
I have thoroughly cleaned the IAC and IAC solenoid plunger. I have thoroughly cleaned out the throttlebody. I have replaced the TPS.
Also, when I disconnect the IAC while it’s running it’s still idles exactly the same with no change.
Can you please give me some troubleshooting steps to continue trying to identify this problem? Thank you
Cargo Master
Joined: Sep 2006
Posts: 2,120
Likes: 390
From: Evansville, Indiana
Did you set the TPS correctly? Book gives a voltage range but .98 v is ideal. Did you erase the KAM (keep alive memory) after the IAC and TPS work were completed?
On the high idle upon cold starting, check the Thermactor Air Diverter valve located behind the upper manifold by disconnecting the vacuum line and plugging it. If the diaphragm has gone bad, it will be a vacuum leak that lasts for the duration of the TAD signal, 60-180 seconds.
Look thoroughly for vacuum leaks first. Do not adjust the throttle plate screw until you do. Also, don't adjust the screw without referencing exactly where it is now. It is impossible to set with other issues going on.
These engines have a weak gasket between upper and lower intake manifolds. I'd check that next. Check PVC.
If you are confident that you have no leak and want to give that screw a shot, again, be sure to reference where it is now. Write it down! With a warm engine, unplug the IAC then back off the screw a bit at a time and see if the idle drops. You are looking for maybe 500-550 rpm. Close to dying. Plug in the IAC and and with luck you'll settle out at 675-700 rpm. If you got the idle to come down it will still want to hunt. You would need to erase the computer KAM (keep alive memory) by disconnecting the ground lead to the battery and turning on the headlights. After five minutes, hook it back up and start engine. Let it run while the computer works out a new profile.
On the high idle upon cold starting, check the Thermactor Air Diverter valve located behind the upper manifold by disconnecting the vacuum line and plugging it. If the diaphragm has gone bad, it will be a vacuum leak that lasts for the duration of the TAD signal, 60-180 seconds.
Look thoroughly for vacuum leaks first. Do not adjust the throttle plate screw until you do. Also, don't adjust the screw without referencing exactly where it is now. It is impossible to set with other issues going on.
These engines have a weak gasket between upper and lower intake manifolds. I'd check that next. Check PVC.
If you are confident that you have no leak and want to give that screw a shot, again, be sure to reference where it is now. Write it down! With a warm engine, unplug the IAC then back off the screw a bit at a time and see if the idle drops. You are looking for maybe 500-550 rpm. Close to dying. Plug in the IAC and and with luck you'll settle out at 675-700 rpm. If you got the idle to come down it will still want to hunt. You would need to erase the computer KAM (keep alive memory) by disconnecting the ground lead to the battery and turning on the headlights. After five minutes, hook it back up and start engine. Let it run while the computer works out a new profile.
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Pull the codes first off, lots of info on the net how to do it just get a code reader.
https://www.innova.com/product/detai...ader-1981-1995
If nothing stands out get the old vacuum gauge out, if you have a vacuum leak that will identify it.
https://www.innova.com/product/detai...ader-1981-1995
If nothing stands out get the old vacuum gauge out, if you have a vacuum leak that will identify it.
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