High idle, hesitancy and dying after replacing TPS? ('96)

Doing a tune-up on a newly acquired '96 4.0 AW4/2WD. Got the P0122 code after pressure washing the motor, bought a new TPS along with spark plugs and air/oil/fuel filter.

While installing the new TPS (a $52 BWD unit from O'Reilly's), I disconnected the upstream O2 sensor, IAC, TPS and a fourth connector (a ceramic looking one that ties into the same loom) and sprayed them with WD-40.

Now, the thing runs like a pile of steaming pooh.

It immediately revs up to 2-3K upon starting, and gradually comes down to settle @ 1300 RPM. It’s somewhat boggy/hesitant upon revving and dies instantly when you put it in gear. Also, the cooling fan kick in regardless of temp. I haven't been able to read the code properly, but the CEL is flashing 34 or 322 – none of which makes much sense?

Please advice?

I wish I could help more, but I did read the other day its not too uncommon for TPS's to be bad right out of the box. If its not too much trouble you could probably get it checked at the parts store.
AutoZone offered to check mine.

WD-40 is a poor choice. It may work well on high voltage spark, maybe even 12-14 volts, but it has some resistance and is IMO a very poor choice for sensor circuits that may operate from 0.1-5 volts.

Try a simple test, clean your Ohm meter leads off with some solvent, then touch them together on the 1 ohm scale. Then spray a lead with WD-40 and try it again. With the WD-40 chances are you will have some measurable resistance.

Any kind of oil is IMO bad news in any low voltage (sensor) circuit, "garbage in and garbage out" is an old computer axiom. Bad or inaccurate readings from your sensors into the PCM are unlikely to give satisfactory results. Even the oil from your finger tips can affect the resistance reading on your meter. Any oil on the sensor connectors is likely to affect the output readings to the PCM.

What you're saying has struck you my mind, could the lube itself create resistance and erroneous current paths within the connectors? But on the other hand this has been standard procedure on numerous previous vehicles with no similar effects.

And it doesn't explain the cooler fan whose connector I haven't touched?

I had very similar hesitancy problems on my 92 w/ 230K but without the dying. My problems were the 2 pcv intakes under the valve cover. They were completely clogged giving the computer a false reading and fattening the motor. Cleaned them and now it runs like a top. Pull the PCV elbow off and look down in. If it looks like there's a bunch gunk in there I would pull cover and check.
As far as the high idle I took mine to a mech 2 weeks ago. He said comp controls all idle functions and he could not get it to read with OB2 reader. He said in his experience when this happens comp is shorted out. Mine still has wild erratic idle swings from 0 to 1500rpm. Went to pull comp from salvage yesterday but the ones with #'s close to mine are already gone. Hope this helps

Unlikely the WD-40 created any shorts. but it does/can cause extra resistance in my tests.

On some models when the temperature sensor is unplugged, the aux fan comes on. Leads me to believe you may have an open circuit in the engine temperature circuit, either a bent pin, maybe the WD-40 or for whatever reason an open circuit.

May also be a short in the engine temperature circuit. Which kind of fits in with what BLK Cherry was suggesting, except the PCM short may not be internal but external. A sensor short can also have a cascade effect, in my experience, one sensor shorts out and messes up other sensor PCM inputs or values.

I'd clean the engine temp. connector, ohm the engine temp. sender and ohm the engine temperature sender ground (which is likely to be the same ground as the TPS).

I Usually clean the connectors with a quality contact spray. Contact spray usually helps remove oxidation on the connector pins, displaces moisture and is designed for this application. I'd ask the guy at the local electronics store what he recommends. Like most things there are good brands and not so good brands. The stuff I use is years old (a little goes a long ways) and works really well.

Thanks for the advice, but I'm fairly certain this is a sensor/engine management issue. Motor was running like a clock before I replaced the TPS.

I'll go over all connectors again. Maybe give them a whiff with a gas duster and then apply whatever recommended electronics spray (won't this also contain some amount of oil?)?

How do I proceed if there is a short, external or otherwise? Also, not having an ohm meter, how can try to pinpoint the source through elimination? Motor shuts off when you unplug the TPS connector and will rev up when you unplug the O2.

I ordered an OBD2 reader adapter so should be able to confirm the codes fairly soon.

Mine was running like a top. I filled up with gas, fired it off and all the problems began.

1996 is OBD-II, and self diagnostic. Download the CEL trouble codes and use them to help focus your troubleshooting.

Use electrical contact cleaner, not WD-40, which is neither a cleaner nor a lubricant.

Buy a genuine Jeep TPS. Cheap crappy "Lifetime Warranty" parts are often out of specification or even failed right out of the box. Many times they have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors.

TPS failure may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

The TPS is mounted on the throttle body. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the
position of the throttle blade changes, the resistance of the TPS changes. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5volts. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction witha slow engine return to idle speed symptom.

I've found contact spray to work better than generic electronics spray. Contact spray tends to do a better job of removing oxidation on connector pins, most electronics spray is just a cleaner.

I usually troubleshoot from easy, then hard, then spend money. In my experience better than 60% of the time it is something simple and not a component failure.

You really need an Ohm/Volt meter to eliminate most of the simple possibilities. Along with a good visual inspection. I use a flashlight, even in the daylight, it helps me focus, narrows my inspection (tunnel vision) and almost forces me to work in a systematic approach.

Swapping out components on a hunch can get really expensive very quickly. Code readers tell you a sub system or sensor is out of value, not why it is out of value. It may be the sensor, it may be the wiring or a connector, the only way to know for sure is to test. When you run out of tests, then is the time for best guess parts swapping (desperation).

96 is a hard year to troubleshoot, the FSM is hard to find and it is a transition year. It may be mostly a 97 or mostly a 95 or a combination of both.

A fairly common problem is when a mechanic builds in a problem, trying to find or correct another problem. Like pressure washing a motor to find an oil leak, then having electronic issues. Or swapping out a part and tearing a wire loose or bending a connector pin. I've done it, I imagine most mechanics have also.

Best guess is your TPS/engine temperature sensor ground is open or really bad. Just a guess. Why it is open or very bad can be for numerous reasons, oil covered connector, pin backed out of a connector (it happens), some wire just barely making contact and gets broken completely and/or a wire pulled loose while moving the harness around etc. I may be wrong, but that is where I'd start.

I second the 60% simple and don't throw money at it.

I did the latter and it ended up being simple.

Thanks for valuable input, guys.

Here's an update:

Went through and dried out/cleaned out the aforementioned connections, plus adjusted the TV cable (had forgotten that I played with it). Now the vehicle works tons better, responsive and tranny is silky smooth through all gears. However, there is still a few quirks. The idle is now constant at 1250 RPM and the cooling fan will cycle every 10 second (with defrost/AC on). Additionally, I suspect it's running somewhat rich (judging by the MPG).

And I've also realized that 1996 is kind of a difficult year. I originally got the wrong TPS from RockAuto and had to go to O'Reilly's and get one for a 1997.