High Idle, Pulsing Idle?

[SolidGoldCaddy]

just started idling at about 1200 , but only when i come to a stop, and it sometimes pulses at idle too....any guesses on what it could be, and possible troubleshooting so i know what part to buy, i was thinking a vacuum leak or idle air control......???? help please fellas

 

[MazdaGreg]

High Idle - Sounds like a vaccum leak. i'd start there...

 

[marragtop]

Check the connections at the vacuum tree located on the drivers side back by the firewall. It could also be the IAC.

 

[BuffaloXplorer]

Try cleaning the IAC and check the vacuum connections as previously stated.

Cleaning the IAC

 

[SolidGoldCaddy]

Try cleaning the IAC and check the vacuum connections as previously stated.

Cleaning the IAC

just cleaned the iac, and checked for vacuum leaks, and it still does it , but now its pulsing while accelerating and driving at constant speeds....wtf, im out of guesses? is my iac bad? anything else ignition wise that could be wrong? i checked the wires and connections and they are all good, but it also rins about 3k rpms in o.d. at about 70-75 mph....i do have it in 4wd but i didnt think it would hurt it...????

 

[MazdaGreg]

unplug the IAC and see if it still does it. When you unplug it, the idle should settle down to around 500 or so. If it doesnt settle down, it still sounds like a Vaccum leak. If it does settle down, Sounds like it could be the IAC, a leaky Air Snoot (Between the MAF Sensor and the INTAKE,) or possibly a MAF Sensor

 

[SolidGoldCaddy]

unplug the IAC and see if it still does it. When you unplug it, the idle should settle down to around 500 or so. If it doesnt settle down, it still sounds like a Vaccum leak. If it does settle down, Sounds like it could be the IAC, a leaky Air Snoot (Between the MAF Sensor and the INTAKE,) or possibly a MAF Sensor

ok so say i unplug it and it doesnt idle down, then should i replace the iac and maf? just to be safe? anything else it could be before i spend the $ to do that? by the way , thank you for your help, your very timely in your responses and i appreciate your help.....

 

[aldive]

Have you checked the fuel pressure?

 

[MazdaGreg]

Woah! I wouldnt start throwing parts at it. That will get expensive Quick!

If i were in your shoes. The first thing i'd do would be check for codes. I bet with an erratic idle that bad, you'll come up with something.

After you have pulled codes, i'd try unplugging the IAC when the engine is somewhat warm. It should settle down. If it does, then it shows you that either the computer is playing with the idle. if it doesnt, you realize that it has nothing to do with the computer system, and then it would be some kind of vaccum leak or something else.

check for codes first, and then come back to us. I would not start buying parts yet, you can diagnose this.

Just for kicks, when the engine is running, pull the pcv valve out of the valve cover, but do not unplug the vaccum line off of it. See if it's leaking. my idle was very erratic when my pcv valve failed. I had never had that happen before. The pcv should not allow any vaccum through when you pull it out of the valve cover.if you do, plug that line and see if your idle settles down.

 

[SolidGoldCaddy]

Have you checked the fuel pressure?

no...

 

[SolidGoldCaddy]

Woah! I wouldnt start throwing parts at it. That will get expensive Quick!

If i were in your shoes. The first thing i'd do would be check for codes. I bet with an erratic idle that bad, you'll come up with something.

After you have pulled codes, i'd try unplugging the IAC when the engine is somewhat warm. It should settle down. If it does, then it shows you that either the computer is playing with the idle. if it doesnt, you realize that it has nothing to do with the computer system, and then it would be some kind of vaccum leak or something else.

check for codes first, and then come back to us. I would not start buying parts yet, you can diagnose this.

Just for kicks, when the engine is running, pull the pcv valve out of the valve cover, but do not unplug the vaccum line off of it. See if it's leaking. my idle was very erratic when my pcv valve failed. I had never had that happen before. The pcv should not allow any vaccum through when you pull it out of the valve cover.if you do, plug that line and see if your idle settles down.

ok ill try that today, and see about codes on monday or if i go to autozone today

 

[MrShorty]

www.dalidesign.com/hbook/eectest.html under tests describes how to pull codes with a jumper wire (paper clip works) with the codes coming out as flashes of the CEL, if you don't want to go to autozone or wait until Mon.

You said it is "jerky" when driving, and you are using 4WD. Is it possible the jerking is the drivetrain binding up from running on pavement?

 

[SolidGoldCaddy]

www.dalidesign.com/hbook/eectest.html under tests describes how to pull codes with a jumper wire (paper clip works) with the codes coming out as flashes of the CEL, if you don't want to go to autozone or wait until Mon.

You said it is "jerky" when driving, and you are using 4WD. Is it possible the jerking is the drivetrain binding up from running on pavement?

not so much jerky as it was running like it was missing, like solid constant rpms, then a quick abrupt dip about 300 less than what it was running at, and then right back at it....i have no idea, and i just went out to start it and warm it up to try the iac thing, and its not idleing high anymore, ill have to see when it does it later i guess....this thing just loves screwing with me...

 

[south59]

I'm having the exact same problem. I unplugged the IAC connecter while it was idling, and the RPM's dropped to about 500, and then the engine died shortly after. What does this mean?

 

[south59]

Just to follow up.. I did a KOER test and got a 411 code - Idle speed system not controlling idle properly (generally idle too high) - ISC.

 

[homerbundy]

I'd try to swap the IAC and maybe also the MAF Sensor for some used parts first. You can get them for little money at any junkyard. Or maybe you know somebody in your neighborhood with a 91 - 94 Exlporer who lets you try his...

If the problem still occurrs you might want to check for dirt in the throttle-body. Even only a dirty air-filter can already cause symptoms like that. All this doesn't mean much work and no big $ for parts but it helps to line out some possible causes...

 

[SolidGoldCaddy]

ok so i unplugged my iac and it dropped the rpms about 500 or so, but it still runs a little rough with iac unplugged. then, while i had the iac unplugged i also unplugged the maf, and it dropped it even more....i think i will try to replace the iac, and see what happens, anyone else have a better idea??? thanks to everyone for taking time out of your weekend, to pick your brains...it is greatly appreciated!

 

[MazdaGreg]

That sounds like a plan to me. I'd probably pick up a can of electrical parts cleaner, and clean the MAF while you were under there, just to be safe. See what happens...

 

[SolidGoldCaddy]

well it just keeps getting better, today i went and got...

A) idle air control, and installed it......NO CHANGE

then i went and got

B) Mass air flow sensor, and installed it.....NO CHANGE

now i have a few theories about whats going on now that those things are replaced..

1)water pump is shot; heres why i think so
A)when start up and drive to work the gauge indicates the temp on the hot side of the normal bracket, almost out of the "normal" area...and stays there, or drops very little....upon stopping and acceleration to get it up to speed of around 35-40 mph, the truck gets a little jerky, but slowly and gradualy evens out....i believe the pump is being turned and spun at the higher rpm on acceleration and is pumping a small amount, then when the r's drop when i get to speed it isnt pumping as much and the jerky motion fades out.

2)electrical sensor other than what i replaced?
A) i have no more guesses what other sensor could cause this...throttle position sensor possibly?

any other guesses or advice would also be appreciated...heres the problems as of today

A)running hotter than normal but technically not overheating
B)shimmy or jerky motion on acceleration
C)rpms have dropped somewhat to normal(as far as i can tell) ranges,its at about 2500 @ 65 mph
D)thermostat IS opening as the upper hose is hot
E)checked ALL vacuum connections under the hood, and all were tight and sealed
F)Replaced parts listed above, IAC = 58.00, MAF 105.00

ill check this in the morning, but now that i noticed the temp running hot, it think a new water pump might lower the rpms to actual normal idle by putting the "load" back on the engine and making it work. i dont drive it over 65 cause im afraid of overheating it and i dont want to have to stop and wait for it to come down, plus its winter and i think thats the only reason im not overheating.....any input on how to confirm that its the pump would be great...thanks

thanks again fellas! you guys know what your doing...

 

[SolidGoldCaddy]

That sounds like a plan to me. I'd probably pick up a can of electrical parts cleaner, and clean the MAF while you were under there, just to be safe. See what happens...

p.s. did everything that you listed before i bought anything!