b.mcdaniel.2009

I've try to do alittle research about this problem and I've found it to be common, but no one posted what they have done to fix it. My Jeep is a 99' Classic Auto with only 89,000 miles....Anyone have any thoughts or suggestions?

tjwalker

The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is 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 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

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: -

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

• 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 with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

89Laredo

Just by the nature of things, the trans will shift a little harder when its cold...

b.mcdaniel.2009

Going to test the voltage right now, thanks so much for the info. If the TPS reads bad Advanced Auto has to different one's instock, Elderbrock and BWD. Any suggestions on which one to buy?

b.mcdaniel.2009

Bought a new T.P.S., Accel tune up kit, and Ram air intake and it runs smoother, faster acceleration but the transmission still shifts hard when its cold. Only for about the first 5-8 minutes. Is there anything else to check before I start looking for a new tranny????

brutalxj

How long do you let it warm up? I wouldn't get a new trans over a hard shift just a lack of one.

b.mcdaniel.2009

It gets parked in my heated garage but before I drive it I let it warm up for about 8-10 minutes while I put my coat and boots. Engine temp gets to full operating temp 200*.....

Also It was parked outside for about 8 hours today, I had to move it real quick, cold engine and it took about 5-10 sec after I shifted it into reverse for the transmission to go into gear???? Weird. It acts like a pump that has to prime itself.

blinkbears

My 88 started doing the same thing. No clue why.

tjwalker

The test that may tell the story would be to take it to a tranny shop and park it there overnight. First thing in the morning, have them hook up the gauge and check the line pressure and monitor it as it warms up. That may tell the story.....a marginal tranny with internal issues may have marginal line pressure out of the gate.

b.mcdaniel.2009

Hey tjwalker, do you think this is a mojor issue or should I really not worry about it unill it gets worse? After it "warms up" it shifts like butter.

jonw

I have a 99 jgc, and it seems to be doing the same thing. I asked a mechanic about the issue and he said something about internal seals in the transmission breaking down. He called it "morning sickness": he said once the seals warm up, they expand and that is why the issues stop. Is there any validity to this claim? Can the seals be replaced alone or does the whole transmission need to be replaced?

tjwalker

There are a few things that can cause low internal line pressure in a transmission.

But don't get ahead of yourself. Get a line pressure test done on a stone cold engine and then you'll know for sure. It won't cost you much.

Good data = Good decisions

Trev1006

Sea foam trans tune, you can get it at auto zone. It works wonders, just dump in on top of the fluid in there and leave it in there. I've had it fix ones that wouldn't even shift ! The sea foam washes the varnish off internal parts and can bring internal seals Back to life a little. When I bought my most rescent mj it wouldn't even shift up or down from second, sea foam in it, that was 150,000 mj ago. Keep your trans serviced too, Ibe seen too many trans filters from these jeeps completely clogged! The thing with it not moving in reverse sounds like a clogged filter or low pressure.

ZINGGG

I've never heard of anyone seafoaming a trans... Doesn't sound like the greatest idea... I'd definitely consult a professional before doing something like that

tjwalker

Seafoam makes a special additive which is designed specifically for the transmission. Trans Tune. Not to be confused with Seafoam Motor Treatment, which is a totally different product.

http://www.seafoamsales.com/trans-tune.html

I have seen people have some luck with their Trans Tune product, but I have two friends in the transmission business and when an additive is required (rarely), they recommend LubeGard in the red bottle. I'm not a big additive guy, but I've seen LubeGard do some miraculous things, especially for a transmission that has not had reasonable fluid change intervals.

This all being said, there isn't any harm in trying either of these products, but if the problem is internal to the transmission, an additive is not going to help.