IAC issue 1993 X 4WD 125K runs too good?

[woknap]

Hi
I would like to start by saying thanks for this web site.
I have read posts about IAC so now I am slightly smarter than before.

I cleaned my IAC because my RPMs are too high at 1500 to start, 1100 at idle, and goes up by 500 to 1600 when I put car into reverse; wasting gas and trans not down shifting down soon enough because high rpms.
Gave up on cleaning so I bought new one, thought it helped in the first test drive, but next day everything is same as before.

I am now driving with disconnected IAC to test what happens; so far 1100 rpm start up, 750 idle in park, and 600 in drive with foot on brake, and no reving of rpm when shifted into reverse.

My next project was throttle sensor, but would like to finish one thing at a time.
thanks
greg

 

[natenkiki2004]

I could easily be wrong but I believe if you disconnect the IAC and get better performance, that means you have too much fuel being pumped in and then the computer opens the IAC to compensate for the extra fuel and boom, high revs.

How are your spark plugs? What kind of color?

I know this doesn't help, I'm more thinking out loud on this one.

 

[woknap]

I need "outloud", even yelling is ok...lol
I know I need to plug the IAC back in, but it just seems like an out of control choke.

original plugs were in when I bought it a few hundred miles ago...mostly carbon, ash deposits, moist, and a plug looked worn but "clean"
I changed plugs, wires, rods, rockers, fan, fan clutch, cleaned radiator in and out, rad hoses, heater hoses, trans pan drop and filter, and cleaned IAC and MAF.
I want to do Throttle position sensor next(voltage) and check fuel pressure next.
I have been recording miles and gallons used and seem to get about 14+ mpg.
I just found out it is hard to start without IAC plugged in; have to push gas pedal till it has run 10 to 15 seconds.
You recommend gas pressure check next or u thinking injectors?
oh, I do have seafoam in gas, but this high rpm has been since before that
thanks
g

 

[natenkiki2004]

While it's running, pull the vacuum line to the fuel pressure regulator. If you see gas dribble out, that thing is toast and needs to be replaced. It could be leaking badly and sucking extra fuel into the upper intake manifold.

If that's bone dry, that's probably not your suspect. Test the intake air temp (air charge temp) sensor and the engine coolant temp sensor. Your computer might think the engine is always cold and put more fuel in.

If all that's good, maybe the O2 sensor? There's ways of testing it but you have to run the engine while backprobing the sensor. That's too much of a hassle to me, especially around burning hot exhaust pipe, I just replaced mine.

Also, check for vacuum leaks. The plastic lines like to rub against things and chew a hole in them. I got tired of chasing mine and replacing boots, I just went with some silicone hose. Absolutely love it.

 

[the_don]

+1 for a vacuum leak, check all the lines,intake mani, throttle body gasket,brake booster, and transmission modulator