Plugging the EVAP makes no difference. I replaced the TB gasket. No difference. The wires have pulses per the video. Attached is a picture of the pintle at about 10 counts. Almost fully seated. Seat and pintle are clean. No matter what I do (cracked open throttle plate, fully closed throttle plate) it idles at 900 rpm by adjusting the IAC counts. They've been at 0 when the throttle plate is slightly open and 20+ when the plate is fully closed. Rpms are always 900. I'm about sure the computer is commanding these rpms.

If I plug the IAC pintle hole, I can bring down the rpms, but I still have to let some air through or it will stall.

 

Since it seems that the computer is wanting the car to idle at 900 rpms no matter how far closed or open the the throttle plate is (within reason), I'm thinking it has to be something that is causing the computer to do what its doing. The truck is just a stock 2.2 and I think it unlikely that anyone had the computer "tuned" for a higher rpm at idle. I think maybe it has to be something providing a signal to the computer that is causing the to increase the idle. My thoughts include the following:

1. Map sensor. The reading at idle seems a little high. It has come down to 35 psi, but from what I read it should be around 27. I've ordered a replacement, but it is not here yet.
2. Weak alternator. I've looked back at screen shots of my OBDII scanner program and see that the highest "Vehicle Voltage Level" the program reads is 13.2v Its been 12.9v @ 902 rpm, 13.2 @ 2419 rpm, 13.2 @ 895 rpm, 13.2 @ 900 rpm. The program has the following parenthetical for this PID: "Usually the input voltage at the diagnostic connector." I'm going to take some readings at the battery with a DVM this evening to double check the software. If the alternator is weak and not putting out a charging voltage at idle, I figure it is possible the computer is commanding the truck to run a little faster so that the battery charges. Do you agree? I would also expect to see the charging voltage at at least 13.5v. And I would have expected it to put another volt above that at 2,400 rpms and certainly not the 12.9v reported. Again, this is what the software is showing, so it bears double checking.

 

It seams reasonable to assume that the computer wants this idle, I don’t think that the computer tries to compensate for low charging voltage with rpm. The MAP sensor could be involved, I can’t get an idle reading for you to compare because I have a 4.3. Does your engine temperature get up to 190 when driving, It was around 160 in one of your screen shots?


George

 

Yes, I've seen it up at 190 or so.

 

You have been through all the usual suspects and seem pretty thorough. I went back through the service manual to make sure that I am not missing something but nothing new except what I mentioned early on that a mainstay of proper diagnosis at the pro level is commanding different idle targets with a bi directional scanner which is beyond most diy’ers unfortunately.

George

 

Couple questions,
In the morning after an overnight cold soak KOEO have you compared IAT & ECT temps? Should be the same or within a few degrees degrees of each other.

When you first start engine do you get an rpm flare up for a quick second?

 

The temperatures at those two sensors are identical after the car's been sitting overnight. When I turn it on I do get RPMs up in the 1500 range but they go down very quickly.

I'm starting to think that I may have a vacuum leak at the injector o rings. I had to remove them to clean them, and I may have gotten some gunk on one or more of the sealing surfaces when I put them back in without removing the intake manifold. When I spray the accessable injectors with brake cleaner or propane, the RPMs do not change, but I can see the fuel trims change a little bit -- like as much as a 10% decrease (with brake cleaner, the propane doesn't seem to bring it down as much) wich seems to indicate pirate air is getting in. I'm not sure if any of what I'm spraying is getting into the intake, but I've got to have the plastic air intake off to do this so it is possible that's what I'm seeing with the trims changing. That may be just enough of a vacuum leak at an injector to be causing these problems and keeping the car at 900 RPMs despite the computer's efforts. Or not. I don't know. This seems to be more likely than someone tuning a four-banger to run at 900 RPMs. I hate to pull the injectors again, but I really like to get this resolved. This time I'm going to pull the whole intake.

 

Am I understanding correctly that you are saying you didn't have the high idle problem previous to the work you've been doing? I thought from your first post the high idle issue was one of the problems you were fixing in the first place, no? Don't go to far the rabbit hole of removing the intake yet. You might have a simpler answer to try first if this started after your other repairs. It involves the adaptive values stored in your PCM.

 

I bought the truck not running. I had to clean the injectors, replace fuel pump and a few other things to get it to run. This 900 rpm is what I got when it finally started. I don't know what it did before, but I think it sat for about 4 years.

By all means, let me know how to clear the adaptive values in the ecm. Thanks

 

If it sat for 4 years, I would say it has lost those values already.

How much did you drive the truck after you did both the TPS replacement and the IAC replacement? Did you get up to highway speeds, go up and down hills (with some long coasts on hills)?

Did you do the IAC reset when you installed the new one? (KOEO for 10 seconds, OFF for 5 seconds, then immediately start the truck)?

I have to admit…even though in the morning the ECT and IAT are reading the same in the morning…I’m wondering if the ECT/circuit is not reading correctly at higher temp. Could be wrong on that, but I would investigate personally.