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idles at 2500 RPM

G

GinisKratos

NAXJA Forum User
Location
Centralia, WA (Olymipa)
So my new fuel pump went out and i replaced it, again. fired it up, ran good, shut it off, restarted it, ran fine.

Few hours later i went to take it for a drive. it fired up and sometimes jumps up the first few second like all cars do but settles down to 750-1000rpms... but now its going up to 2250 and staying there for about 5-6 seconds, then going up to 2500-2600 and stays there, the peddel feels funny also, like its already pushed in, used my foot and tried to pull it back but nothing.

I pulled off the air filter hose to see what was going on in the throttle body but everything looks normal. flap is shut nothing extra should be going in there. TPS, MAP, all that was replaced back in march.

Any ideas would be super. this is getting old fast heh. :cool:

PS its a 1989 4.0 heh guess you all might need that to help lol
 
I got some cleaner, made sure nothing was gumming up the throttly body. but didnt fix it. disconected the batt to reset the computer, maybe something was fubar'ed when i was testing the fuel pump power and all that. I'll give it a bit and see if that helps.

Ed
 
IAC, Idle Air Controller, also called an idle stepper motor, is probably dirty and sticking. Many good threads on the beast here. It is next to the TPS on the throttle body.

Did you calibrate the new TPS and check the TPS ground quality, less than 1 ohm, with an ohm meter?
 
no i didnt check the TPS but i did find that the IAC seems like it was stuck or something. its sucking in alot more air then it should. I took it off and cleaned it, but didnt seem to work, ill try again tomorrow.
 
GinisKratos said:
no i didnt check the TPS but i did find that the IAC seems like it was stuck or something. its sucking in alot more air then it should. I took it off and cleaned it, but didnt seem to work, ill try again tomorrow.
Click to expand...

ALL of the idle and starting air supply goes through the IAC inlet port, the small opening in the top of the throttle body. Don't know how you could tell if it feeding too much air? Unless you partially blocked it with a thick metal plate (don't use your hand to block it, if you value it!) and saw the idle drop? IF that happened you have either no power to the IAC (bad relay, wire, or connection?) or the IAC is damaged. IAC's do get damaged!
 
you can just hear the amount of air going in there. sounds like a turbine starting up heh, i covered it with a glove so that some air could still go though and it droped down to normal idol... even enough for me to be able to drive it into the shop lol.

The IAC was new 9 months ago, was the first thing replaced when i bought it, the prev owner said it was bad and had te part right there, it ended up not being the prob but the MAP insted.

I checked the power going to the IAC, not sure what should be there but there was 10.7v across 2 pins and 5v across another.

I dont really understand how the IAC works, when power is applied should the plunger go into the TB and close the hole to let less air in? or should it start out extended? I have no idea what a good one looks like so i dont know if this one looks broken or not heh
 
I've had lots of problems with my iac's. Everytime i reset the comp or unplug the battery, i have to manualy set the iac. my iac is only held in by the top bolt now, for over a year, no leaks ever. This is how i set mine: take it out leave it pluged in with the ignition off, pull the sleeve back and unscrew the pintle (valve) a little and test fit it. if you unscrew it to far it wont fit, the sleeve does not turn, just pulls in and out, when i set mine a half turn before contacting the valve seat. then install it. mine will usally idle around 500 at first but then correct itself to around 800. hope this works for you....
 
GinisKratos said:
you can just hear the amount of air going in there. sounds like a turbine starting up heh, i covered it with a glove so that some air could still go though and it droped down to normal idol... even enough for me to be able to drive it into the shop lol.

The IAC was new 9 months ago, was the first thing replaced when i bought it, the prev owner said it was bad and had te part right there, it ended up not being the prob but the MAP insted.

I checked the power going to the IAC, not sure what should be there but there was 10.7v across 2 pins and 5v across another.

I dont really understand how the IAC works, when power is applied should the plunger go into the TB and close the hole to let less air in? or should it start out extended? I have no idea what a good one looks like so i dont know if this one looks broken or not heh
Click to expand...

Do you still have the old IAC? Might retry it if you do.

Have you checked every where for a vacuum leak to the intake manifold? Try blocking the IAC inlet with a hard steel plate, if the engine continues to run, or ties to run at say 20 to 330 rpm you have a vacuum leak somewhere else!
 
i blocked it with my palm and it died, but if i put my glove on there and leave a little gap, it idols just fine, so i know its the IAC. second part thats been replaced in the last 9 months or so thats gone bad again. Lame...
 
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