That's getting gutted today. I seems to be flowing well. Even checked the temp before and after the cat and they are about the same. I pulled the IAC and the plunger moves just a little bit. How far is it supposed to move?

 

The PCM controls how much it moves. You saying you moved it by hand? If so, you most likely damaged it.

 

I didn't force it to move. It seems like it's spring loaded.

 

All I can say is, you really don't want to do that. There is a little motor inside that can be easily damaged.

 

The issue with using 3rd party sensors is that they are rejects that do not pass electrical tests that the dealer parts are subjected to. This is also one of the reasons some don't work properly such as the "new" TPS sensor your running.

I had a run in with that a while back and, I went and spoke to a technical resource about those 3rd party parts.

Most of them are made by a couple of suppliers and are shipped to the dealer only if they pass screening. This is why the dealer parts cost more- because they are pre-screened to TIGHTER tolerances and you pay for that level of screening.

The left over rejects that are not gross failures are then purchased dirt cheap and sold dirt cheap and, it's a perfect setup as the part stores all work a no refund on electrical because they know it may or may not work so, they buy them for 10-20 bucks and mark them up a bit but still way below dealer cost / wholesale and make out like bandits.

The waveform / sine output of many of the 3rd party sensors fall outside the range of dealer spec so, it is no surprise that you get surging. However, that may not even be the problem. Read on.

I've bought 3 IACs and only the dealer item worked 100% of the time. I now only use dealer or pre-screened / fully tested to be functional out of the box for I know it is going to work vs. 3rd party auto stores.

Now, in your case, theres a few different things that can cause surging and or stalling and, one of them is a bad coil- that is a possible failure mode cause and effect- same symptoms.

Faulty ECT will also cause erratic output of the TPS as will a faulty MAP. The MAP is the heart of the EFI system as it measures barometric pressure along with engine vacuum. All work together as a system so, if one is out of tolerence, guess what, you end up chasing it around because your not finding the root cause that is causing the other components to go out of whack.

The IAC will cause a loping in most cases and, you would end up feeling a constant up / down over time. It would pulse more than surge and, it surely would not cause it to stall out while driving under load.

While it would most certainly cause this when IDLING- not so much while driving. Surging- sure, if it's lost it's home position, it will open up, allow more air into the chamber thus leaning out the mix thus setting off a low voltage output at the O2 sensor input which will then immediately trip the PCM to dump more fuel into the mix.

THen, if the IAC now suddenly homes or closes the gap, you've now got a rich engine and not enough air thus choking it thus causing a stall like condition.

SO, in this case, you need to go through and start measuring voltages to see where the root cause for the error is or, you can simply replace one sensor at a time until your seeing normal results.

But, we can't just stop at the sensors for there's two other systems that also have the same failure mode and cause and affect symptoms and that is the fuel delivery system and the EVAP system as well.

Both will cause the same symptoms. Turning hard left or right,under acceleration, and a stall occurs, it could be the EVAP canister. Surging-while accelerating- could be the EVAP canister.

Surging and stalling: low or intermittent fuel pump output. Now your going to have to verify the output under load conditions by simply placing a guage off the rail into the cab while driving. Note fuel pressure. Should be 49 psi ± 5 psi. If it falls outside of that range, your fuel pump is most likely the cause.

Again, remember what I stated about the IAC motor causing the PCM to dump more fuel into the mix? Well, the fuel pump can also cause the same exact symptoms due to a change in the A/F mixture. Then once again, the O2 sensor detects a low or rich fuel condition and sends a high or low voltage at the O2 input at the PCM thus triggering another dump of fuel to balance it out. Then, when the pump kicks in again, now it goes the other way and runs way rich thus almost stalling out due to lack of oxygen.

So, your now looking at four systems to troubleshoot:

the ignition system (COIL)

the fuel system (PUMP)

the sensor / EFI system (MAP, ECT, IAC, TPS)

and the emissions system (EVAP)


My recommendation is if you have the time, do it all yourself. If not, have it scanned at the dealer on an DRB III rack rig and in less than ten minutes, if it's electrical, it will show up right there- done.

If it's the fuel pump, that's super easy to diagnose by testing with a pressure gage. That's a no brainer.

IF you need to test the coil, it's harder to verify without a good rig connected to it and running it on a dyno to simulate a load to see what the output (measured in KV) is. What you can do very easily is to measure the primary and secondary and compare to specs for the coil you have. But, the real test is to measure the high voltage (around 25 K-volts) at the output. This is where the DRB III rack rig comes in handy as you will be able to see this on the scope.

Good luck.

CM

 

It is not spring loaded and, here's how it functions. It's a motion controlled device that is opened and closed by means of a stepper motor.

This stepper motor is controlled by the feedback circuit at the PCM and, each movement of the pintle is recorded and stored in RAM at the PCM. Each motor step is logged and recorded for recall at next startup.

This is why it's essential that you never, EVER touch the pintle, move it or place a side load on it for, if you do, now you've just created a new issue and, that issue is, loss of home position as well as offsetting the MIN and MAX travel values set at the PCM.

Now, when this happens, there's no way to fix this. It's one thing to relearn the home position by clearing the PCM out and performing a new touch down to MAX position with a sensor assembly that has NOT had the the travel position of the pintle valve altered.

By pushing or pulling on the pintle assembly, what you've done is, you've created an offset between the relationship of actual pintle location and motor steps recored at the PCM. Aslo, if it's moved beyond the limit / range of motion, the offset is greater than the stepper motor can tolerate thus damaging the component.

The PCM recalls what's in RAM as the values to use based on history stored in the PCM memory. So, at startup, it accesses those stored values and ouputs x-amount of voltage which in turn, activates the stepper motor to drive the pintle assembly to a preset gap.

If you've pushed or pulled it, you've offset the relationship between the pintle valve and stepper motor. The PCM has no way of knowing this. The PCM will not be able to compensate for it either.

So, what you end up with is the PCM driver circuit drives the motor to say, 250 motor steps to achieve a preset gap amount of .1280 but, due to the offset, the reality here is that the gap may end up being .3000 thus allowing huge amounts of air to flow in at startup thus yielding poor starting, rough idle and other anomalies.

Now, when the ECT input reads around 160-180°F, the PCM now goes into closed loop mode. At this point, the PCM now adjusts the gap at the IAC by changing the voltage as - or + voltage. The stepper motor now adjusts the pintle valve to it's running position. Again, same thing applies here as the gap may be way off and, the PCM has no way of knowing or being able to compensate. In attempt, it will alter the A/F ratio by means of adjusting the fuel mix. It does not attempt to adjust the IAC too much based on the home position of the IAC motor steps, the PCM can only adjust it within the MIN and MAX values that reside in the PCM. It will not go beyond those values because of damage that would ensue if it were to keep driving the pintle valve into the TB or beyond it's MAX travel length.

So, as you can see now, it's definitely not spring loaded. The spring just helps keep a preload on the pintle assembly to prevent "slop" in the range of motion. In doing this, it helps in accuracy of pintle placement.

Now, if you've moved it then, chances are, you've damaged or gone beyond the limits of the IAC stepper motor thus requiring a new one. If the pintle assembly is bent or side loaded, it will jam inside the IAC body and not seat / align at the TB bore.

Hope this clarifies this component and how it functions in the system.

CM

 

it sure does. i've always heard that you can damage it by twisting/pushing/pulling the pintle and now i know why.

 

UPDATE: Torque Converter was toast. Getting new trans/tc/cooler as we speak.

 

what type of cooler? the tube and fin style isn't enough if it is a stand alone cooler. if you're setting it up with just the aftermarket cooler then you need the stacked plate style like the B&M brand.
don't forget to do a fluid/filter change on the transmission.

 

Thank you cmc. I just completed the Hughes plenum kit and go it all back together, as you said, I moved the pintle and now it seems like there is a massive amount of air being allowed into the port. In turn making it idle at about 1200rpm. Took it around the block and sounds like a massive vacuum leak. Shut it down until I can replace it. Any specific place have a sure fire way to get a GOOD IAC for a good price. I've heard it is common to buy a dud.