Rough Idle/Stalling After Rebuild
12-26-2014, 10:29 PM
#1
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Rough Idle/Stalling After Rebuild
1993 F150 302, S5-42. Just finished a rebuild a couple weeks ago.
After truck is warm if I'm driving and come to a stop, about 1/2 the time it will stall out. Idle also seems to "bounce" once the truck is warm (this is with AC off). I don't have a tach, but I notice the voltmeter fluctuating and can hear the idle go up and down ever 1-3 seconds or so. Strangely, the truck doesn't seem to stall out when stopped and I hit the brakes, only when slowing down or going around a corner and taking my foot off the gas and onto the brake. Could be a bad TPS? Not sure how that would manifest itself.
I've been up and down looking for a vacuum leak and can't find one, I did the starter fluid method at each vacuum connection and none seem to be affecting the idle. Can't see any breaks in the lines either.
After truck is warm if I'm driving and come to a stop, about 1/2 the time it will stall out. Idle also seems to "bounce" once the truck is warm (this is with AC off). I don't have a tach, but I notice the voltmeter fluctuating and can hear the idle go up and down ever 1-3 seconds or so. Strangely, the truck doesn't seem to stall out when stopped and I hit the brakes, only when slowing down or going around a corner and taking my foot off the gas and onto the brake. Could be a bad TPS? Not sure how that would manifest itself.
I've been up and down looking for a vacuum leak and can't find one, I did the starter fluid method at each vacuum connection and none seem to be affecting the idle. Can't see any breaks in the lines either.
12-27-2014, 08:51 AM
#2
1994 F150 XLT 5.8L 2wd
Combustible fluids can help find leaks but only vacuum gauge will completely eliminate the vac leak question.
TPS should read .9-.97 at closed throttle, then when throttle is opened it should increase at a steady pace up to (I believe) 5v at WOT. Check/clean IAC and throttle body blades, did you put a new gasket on the TB and IAC when you put everything back together? Did you remove the TPS from the TB during rebuild? if so did you follow the directions for re-installing it as there is a specific process that must be followed otherwise you will have issues.
Pull your codes, https://www.f150forum.com/f10/how-re...es-obdi-10907/, follow the directions especially for the KOER test and be sure to warm the truck up for a few minutes before starting the KOEO test, once again read and re-read the directions for KOER test. You may have to write the steps down, also will help to record the flashes with a video camera (phone) so you can watch it a few times, or post it here, to ensure proper code ID.
To erase the codes properly start the KOEO test again and pull the jumper wire (paperclip) out when the codes start flashing, this will clear the trouble codes without deleting any driving data stored in the ECU, pulling battery connections will delete the driving data and truck will have to relearn your driving style.
TPS should read .9-.97 at closed throttle, then when throttle is opened it should increase at a steady pace up to (I believe) 5v at WOT. Check/clean IAC and throttle body blades, did you put a new gasket on the TB and IAC when you put everything back together? Did you remove the TPS from the TB during rebuild? if so did you follow the directions for re-installing it as there is a specific process that must be followed otherwise you will have issues.
Pull your codes, https://www.f150forum.com/f10/how-re...es-obdi-10907/, follow the directions especially for the KOER test and be sure to warm the truck up for a few minutes before starting the KOEO test, once again read and re-read the directions for KOER test. You may have to write the steps down, also will help to record the flashes with a video camera (phone) so you can watch it a few times, or post it here, to ensure proper code ID.
To erase the codes properly start the KOEO test again and pull the jumper wire (paperclip) out when the codes start flashing, this will clear the trouble codes without deleting any driving data stored in the ECU, pulling battery connections will delete the driving data and truck will have to relearn your driving style.
Last edited by fltdriver; 12-27-2014 at 08:53 AM.