1994 Pickup Surging Idle
09-07-2014, 06:42 PM
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1994 Pickup Surging Idle
I have a 1994 Toyota Pickup that the idle surges on; howeverit only does it when the AC is on and the break is pressed. When you crank it cold it will not do it butafter a few minutes it will start idling up and down. If I don’t have the AC on it will not surgewith the break depressed. It is my 16yrolds truck. Also it has a terribleexhaust smell all the time.
09-07-2014, 08:24 PM
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6cyl or 4cyl? What rpm is your warm idle? Idle issues are associated with vacuum leaks, and malfunctioning sensors and idle-affecting devices.
As well, how recently have you done a tune-up? If it's been a while, it might be worth it to go ahead and replace the spark plugs, wires, distributor cap & rotor, and air filter.
As well, how recently have you done a tune-up? If it's been a while, it might be worth it to go ahead and replace the spark plugs, wires, distributor cap & rotor, and air filter.
09-08-2014, 08:51 AM
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Sorry it is a 4cyl, not sure on RPM’sbecause it doesn’t have a gage and I don’t have any way of telling. I checked for vacuum leaks by spraying breakcleaner around hoses with motor running and didn’t find any. It has new spark plugs, wires, distributor,cap, and air filter. I also cleaned theintake. One thing I didn’t mention is itis difficult to set the idle. I will setit “by ear” when warm and it sounds correct, but when driving and coming to astop sometimes it sounds a bit high and other times it is so low it will barelystay running this of course is without the AC on. With the AC on it idles up and down almostevery time you touch the breaks. Sometimes it won’t do it for a minute but it will after a minute, othertimes it does it immediately when the brake is pushed.
09-08-2014, 08:52 AM
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Sorry it is a 4cyl, not sure on RPM’sbecause it doesn’t have a gage and I don’t have any way of telling. I checked for vacuum leaks by spraying breakcleaner around hoses with motor running and didn’t find any. It has new spark plugs, wires, distributor,cap, and air filter. I also cleaned theintake. One thing I didn’t mention is itis difficult to set the idle. I will setit “by ear” when warm and it sounds correct, but when driving and coming to astop sometimes it sounds a bit high and other times it is so low it will barelystay running this of course is without the AC on. With the AC on it idles up and down almostevery time you touch the breaks. Sometimes it won’t do it for a minute but it will after a minute, othertimes it does it immediately when the brake is pushed.
09-08-2014, 08:52 AM
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Sorry it is a 4cyl, not sure on RPM’sbecause it doesn’t have a gage and I don’t have any way of telling. I checked for vacuum leaks by spraying breakcleaner around hoses with motor running and didn’t find any. It has new spark plugs, wires, distributor,cap, and air filter. I also cleaned theintake. One thing I didn’t mention is itis difficult to set the idle. I will setit “by ear” when warm and it sounds correct, but when driving and coming to astop sometimes it sounds a bit high and other times it is so low it will barelystay running this of course is without the AC on. With the AC on it idles up and down almostevery time you touch the breaks. Sometimes it won’t do it for a minute but it will after a minute, othertimes it does it immediately when the brake is pushed.
09-08-2014, 05:40 PM
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Not sure why my text is not showing. truck is a 4cly. I unplugged the TPS and it idles high but it doesn't rev up and down with the AC on and brake pushed. Does that mean it is the problem or am I bypassing something by unplugging it?
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09-09-2014, 07:16 PM
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I don't know much about the EFI system in our trucks, but I've heard that unplugging the TPS probably forces the ecu into a closed loop regarding fuel delivery...
To answer your question, probably not(?) But I'm no expert. If your truck is idling high, pressing the brake causes the ecu to cut fuel to aid in braking, which will cause the idle to jump up and down.
To answer your question, probably not(?) But I'm no expert. If your truck is idling high, pressing the brake causes the ecu to cut fuel to aid in braking, which will cause the idle to jump up and down.
09-25-2014, 11:15 AM
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It doesn't do it while the engine is cold. I can crank it up and turn on the AC with the brake depressed and it acts normal. Once it warms up (a couple miles down the road), if I push the brakes with the AC on it will idle up and down. I have turned the idle down so low it bearly runs but it still idles up and down with the motor warm, AC on and brake depressed.
09-25-2014, 11:27 AM
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My truck had similar issue, it was a vacuum line coming off my power steering pump. I just plugged the line and it worked fine
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09-29-2014, 09:09 AM
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The problem is fixed or at least not anoying me any more. Not sure if it was a fix. There is a screw with a spring on it that looks like it goes to the vacuum lines. "Not the idle screw" I turned it to close it about 3 turns and it isn't doing it any more. It didn't seem to effect my idle at all.
10-01-2014, 05:42 AM
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Get your motor into the loping idle condition; then do this:
(only 1 guy ever did it right after I posted it, for 8 - 9 years, and found his leak (on a vette motor) )
YELLOW applies to some GM emissions routing...
(only 1 guy ever did it right after I posted it, for 8 - 9 years, and found his leak (on a vette motor) )
Schrade wrote:
Loping idle can be a vacuum leak. Try this:
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Loping idle can be a vacuum leak. Try this:
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Last edited by Schrade; 10-01-2014 at 05:43 AM.
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