So, yesterday I noticed the idle was higher than normal. In drive I'm at 950 to 1000 rpm and in park it's about 1150 to 1200. It's kind of like a cold start but never backs off and does this when things are warmed up also.

I replaced the IAC Valve about a month ago cause I got tired or cleaning it. The condition was a low idle and fluctuation when I came to a stop.

To test for the new conditions I have been reading that if I pull the plug on the IAC that the idle should drop if it's working?

If there is no drop in RPM then it could be the TPS?

 

A gas motor runs on airflow through to the cylinders with a small amount of gas injected for expansion just before ignition occurs.
Think on those terms.
.
If the idle does not drop with the connector removed, either the IAC is stuck open or there is another source of air getting into the motor's intake tract..
.
The TPS is only a 'position' sensor. It does nothing for airflow or idle speed unless it is jamming the throttle shaft from mechanically going closed..
.
Remove the IAC connector first to see the result, then go from there.
Good luck.

 

Bluegrass,

I got the info from a few of your responses and wanted to make sure I understood it correctly. If the idle drops when I pull the connector then that means it is something electrical?

 

Were trying to diagnose before you pull the connector.
Remove it first to see what reaction you get.
At this point you can't tell if it's normal or a held open.
If the idle is high and above normal and drops when connector removed, it's not the IAC.
If the idle drops from a normal idle, the IAC is doing it's job and there is no problem at that moment.
You must get to this dividing line first.
Good luck.

 

I'll give it check when I get home and go from there.

Thanks!

 

I pulled the connector and the idle dropped from the 1000-1100 down to below normal so it sounds like IAC is not stuck in position.

I looked around and couldn't find any deteriorated vacuum line either. The only line I couldn't get at is the one from the PCV to the back by the IAC. Things were still kind of hot. Started the truck back up (after about 15 minutes) while still warm and the idle was normal again. After a minute or so the idle climbed back up into the 1000-1100 range again.

I didn't stop anywhere to get a read of any codes.

 

Ok. you just proved the IAC is not the problem and it's not anything to do with the TPS.
Something else is faulty and signaling the PCM to keep the idle raised by opening the IAC beyond what it should be.
Your at a point that the use of a Scanner to look at live data to determine what is out of normal order.
It could be the cylinder head temperature sensor, a stuck open thermostat or a harness issue.
.
Here is how the idle is "normally" controlled.
In program, the idle table is loaded with a value of 750 rpm +/- 50 for hot idle. The idle feed back for correction comes from the crank sensor.
This table is shift-able to include cold starts and other control functions such as A/C, power steering load changes and electrical loads to keep the idle stable and stall free.
As you see, something is causing the idle to be out of spec.
Your done guessing until some one takes a technical look at the live data and sees where the problem likely stems from or a code is set that leads to the fault.
Good luck..

 

Thanks,

I'll bring it to autozone or one of those guys at lunch and see if there are any codes showing. If not I'll have to bring the truck in for a scan.

At this point in my trucks life I should invest in a scanner.

 

I now have a serious problem!

I got to work today and noticed that wipers and windows were working real slow.

I parked and let it sit for a minute and got nothing when I tried to start the engine in park. Put in neutral and got a little crank but then just got the clicking. Gauges maxed out twice and then went back to zero. Now nothing (lights, locks, windows, radio, heater fan....) electrical is even working. I'm dead in the water now 20 miles from my tools.

Battery is less than 6 months old and terminals are clean. I don't recall the gages reading anything out of the ordinary. I had no check engine lights or stuff come on either.

CRAP!!!

 

okay, so being dead in the water I looked around the floor of the pickup and found an 8 and a 10mm socket and ratchet. I pulled the alternator and went back in to work. At the end of the day a took a work truck to the zone and the battery was down to 11 volts and the alternator failed a diode and regulator test but passed the rectifier test.

Charged the battery and installed the new alternator and the idle is back down to normal (600-650RPM in gear).

Truck ran fine but I did notice the IAC acting up at 65-70 when I took my foot of the gas when people came into my lane.

I'll have to keep an eye on things for a while but I think the IAC is loaded up from driving with the idle up. I-287 in Jersey at rush hour is bumper to bumper and stop & go everyday.