high idle problem

[tigercat]

my idle is sometimes around 1500-2000 rpm when driving around some times and then puting it in neutral or park but sometimes it is perfectly fine it usually hapens after long trips. but the wierd thing is the check engine light doesent always come on when it happens. any help of what it could be is appreciated.

 

[tigercat]

please

 

[boggs1227]

first thing would be to get the codes read ....that alone may tell you .

but if i were to guess ....check for vac leaks .when i got my transmission back in the truck and was driveing it for the first time from ammco i notice the idle was way to high and took for ever to drop back down to idle when stopped ...took it back and they adjusted something ( so i'm thinking that when they rebuilt the transmission ) they installed a new modulator most likelly a adjustable one so maybe that what they did cause after i got it back the second time it was perfect like the day i took it in to have the work done.


just a few ideas .

 

[tigercat]

i dont hear any hissing could it be something else? like the o2 sensor

 

[tigercat]

please

 

[tigercat]

please i need to know so i can get what i need

 

[boggs1227]

i don't think that a bad o2 sensor could be the cause of a high idle condition .the o/2 sensor is whats at the end of the fuel management line ...it's gives data back to the computer to let it know how to curve the fuel metering to the engine for best mpg .

.....you really need to get the codes check if the cel has or is going off .


i don't think the 92's had egr .... but when my dpfe module was bad and it threw a code 327 . while being bad the engine would surge and power would be on and off while going down the road .idle would be at around 400 rpm's then shoot up to 1100-1200 then back again .

i know you said you can not hear any vac leaks ( can't always hear them over a loud motor )

when you say :
"my idle is sometimes around 1500-2000 rpm when driving around some times and then puting it in neutral or park "
does this mean that after you drive at say 55 mph and your rpms are at 1500-1600 that when you stop they stay the same ?? then at other times it does not do it and is ok ???

try this, unhook the metal/rubber vac line where it goes to the vac tree and see if you see red fluid in it .if you do then the modulator is shot and that in it's self is a "vac" leak .takes only seconds to investigate .

also another thing you may want to try is looking at the tps sensor ...if going bad it may be telling the computer that the throttle body is opened and tells the fuel injectors to send more fuel ....this could be giveing you a vac leak like condition ( engine rpm wise) .and also to check all the wire harness to the main engine management systems ...yes they can go bad i have first hand knowledge about this from mine .......

plus look at the throttel cable for sticking and make sure the linkage on the tb is lubed and working smoothly .... and make sure the iac is clean ( just thought i throw that one in there as a possible cause as well )

but like i said before .....

get the codes read and then we'll go from there ........

 

[Willard]

boggs has given some good advice, it will say a lot once the codes are read.


But you need to give more than a half an hour before bumping your thread. The general rule around here is to give it 24 hours. This is a forum, not a chat room. There are a lot of threads and they aren't always replied to immediately.

 

[tzilla356]

I had the same problem. My check engine light finally came on and I got the codes, but I don't remember what thery were. I had replaced the idle control valve that is hanging off the right side of the intake if you are standing in front of the truck. I also replace the manifold air temperature sensor that is behind the idle control valve on the right side of the intake. My truck runs really good after doing this. Maybe this is your problem as well.

 

[tigercat]

when i drive it and then come to a light everythings normal but if i were to put it in neutral or park it would rev up to 1000-1500 rpm. there is no tranny fluid in the metal to rubber hose. i got the codes read and the guy said it was maybe a loose wire or something

 

[tigercat]

bump

 

[boggs1227]

back to your first post ...you said that not always the cel would come on but sometimes it would...and you got the codes read ,and they did not tell you anything "code # number wise " ??? kinda strange , either it goes on or off it trip the first time...and that generated a code of somesort .

may want to goto another place to have the codes read ...before i got my code reader i called around and i was told that some auto part store will do obd-1 systems but either if the cel light was on or what or if they did not have a way of running the codes they told me sorry ...can't do it . so i was sol till i got my reader.

give this a shot , start the truck and let it be in it's high idle state and then go under the hood and look for any harness you can see with your eye and look for any wires in that harness connector that look like they are really doing a " bad angle...> " and wiggle that one and see if your idle or engine rpms fluctuate any . i had to redo my dpfe connector because the bottom wire that was on the connector had developed a tiny short (plus the keeper tab was broke as well) the wire was doing a 90' degree bend as it went into the plastic of the harness .

if that don't work then try to see if you can check your tps sensor ( voltage wise ) if you got a haynes manual it can tell you how to do this .


other than that blank out the computer and double check all off you engine sensors ( connector wise) and let it sit for a hour with the battery dis-connected ( just to be safe... 20 min is ok but i would just let it sit maybe a hour to make sure it is good and powered down ) then reconnect the battery....then start it up and don't put it in drive just let it sit running for 10-20 minutes and see what it does rpm wise.

maybe a good time to clean that iac while the battery is undone .

 

[tigercat]

i got the codes read and the guy said ther is something with wiring or sensors. i also checked and cleaned the iac and that sensor that screws in after the iac and it had gunk all over it and smelled like a gassy oily smell.

 

[tigercat]

okay i unplugged the iac and the idle was back to normal does this mean it is the iac or could it still be the wiring? and if it is the iac what are the effects of not having it plugged in?