99 T&C 3.8L Erractic RPM

SlimJimRD · 09-19-2008, 10:34 PM

The engine will have erractic idle going from the normal 700 to 2000 rpm. This does not happen all the time but will come and go. Also will die at times. I also notice it can do the same thing while driving where the engine rpm can fluctuate, this does seem to happen while a constant speed.
I have changed the Throttle Position Sensor a couple times and it will help for awhile but then the symptoms will come back after a month or two.
The CEL does not come on when this occurs.
Any thoughts of what is going on and how to fix this permanently?

Thanks
Steve

RIP · 09-20-2008, 11:57 AM

Inspect the PCM connector. Make sure the contacts are in good shape, especially those for the TPS sensor. (61 is 5 vdc power, 35 sensor input, and 43 is ground). Disconect the battery before you disconnect the PCM.

Maybe a vacuum leak? Inspect all the vacuum hoses especially the connections for cracks. Spray brake cleaner (no film) around the base of the intake at the gasket. If the idle smooths or jumps as you spray you may need a new intake gasket. Whatever you use for a spray make sure it doesn't have silicone in it. It will kill the cat converter.

Maybe an Engine Coolant Temperature (ECT) sensor or it's wire harness or connection? It's a main input for setting the idle. Only real way to know for sure is to change it.

The Idle Air Control (IAC) valve/motor is the primary device that controls idle. It is controlled by the Powertrain Control Module (PCM). Trouble is once you open the throttle it's out of the picture.

EDIT

angus10 · 09-20-2008, 12:27 PM

What brand TPS are you getting? The cheap ones are garbage and are know for going bad.

RIP · 09-20-2008, 12:43 PM

Quote:

Originally Posted by angus10

What brand TPS are you getting? The cheap ones are garbage and are know for going bad.

Very good point. I'm on the fence on aftermarket parts but, in your case it may be time to try an OEM part if you haven't.

angus10 · 09-20-2008, 01:09 PM

I have had good luck with Standard Motor Products, but the cheap ones from Autozone and the like are junk.

SlimJimRD · 09-20-2008, 05:02 PM

I have been getting the TPS from Autozone.
Would seem from the posts that I should purchase one from the dealer before going on to other issues? Any reason not to go that route first?
Thanks

RIP · 09-20-2008, 07:39 PM

Quote:

Originally Posted by SlimJimRD

I have been getting the TPS from Autozone.
Would seem from the posts that I should purchase one from the dealer before going on to other issues? Any reason not to go that route first?
Thanks

You can test it when you see the problem again: http://www.autozone.com/shopping/rep...00c1528003c4e3

SlimJimRD · 02-02-2009, 02:37 PM

Okay I finally have checked the TPS based on the autozone site http://www.autozone.com/shopping/rep...00c1528003c4e3
Here is what I should get
Check the output voltage at idle and at Wide Open Throttle (WOT):
For 1997-99 vehicles at idle, the TPS output voltage should be about 0.38-1.20 volts. At WOT, the output voltage should be about 3.1-4.4 volts.

And I measured .361 and WOT of 3.72.
The low is below spec so I have order a new TPS from Amazon that is Standard Motor Products brand part #TH214

Hopefully I can let you know how it works out next week.

Steve

SlimJimRD · 05-30-2009, 02:31 PM

Okay I finally got around to putting the new Standard Motor Products brand part #TH214 on the van. While putting it on I tested the voltage to see if it was in spec.

I measured .387 and WOT of 3.42. At least it is within spec this time.

For 1997-99 vehicles at idle, the TPS output voltage should be about 0.38-1.20 volts. At WOT, the output voltage should be about 3.1-4.4 volts.

Hopefully this time it will work longer than 9 months the Autozone part worked.

Thanks for the advice.

Steve

SlimJimRD · 06-08-2009, 12:41 AM

So the van is acting up again. Wish the change of the TPS would have worked.

I looked at the wiring harness for the TPS and found the wires to the sensor had been spliced in the past. Maybe that is my problem? Based on the second post edit should I pull the connector on my PCM and check continuity to the TPS connector?
Anything else to check as the connector to the TSP looks good.

I got a OBD II scanner from Autozone (loaner).
It shows a P0123 code (no check engine light), TPS/Pedal Positive Sensor A Circuit High Input.

What can I check for the P0123 code other than the wiring?

Thanks

SlimJimRD · 06-20-2009, 03:08 PM

I have gone in and removed the splice another mechanic did a few years ago and soldered the wires and covered with heat shrink tubing. So far no problems even wiggling the wires which did cause the problem before today. Hopefully this will be the last of the TPS issue.

On a (long) side note I traced the wires and found that the mechanic had cut the signal output wire and the ground wire which both now terminate just before the sensor. He then spliced the ground to another ground wire and this does go to 43 of the PCM when I tested continuity between 43 and the splice (the terminated ground is also still connected to 43). The sensor output OR/DB wire is spliced into a white wire that runs along with the black ground wire. These white and black wires are inside the wire protector along with a blue wire. I am not sure if this wiring is original or not and runs from the Transmission Control Module area under the intake manifold and down past the master cylinder. I did not go into the protector to see how it splices to the sensor output. But the sensor output wire does have continiuity with 35 in the PCM and 12 in the TCM so I am guessing that the white wire splices in with the OR/DB wires near the PCM and TCM. The OR/DB that is terminated does not connect to 35 at the PCM any longer.
I hope the other splices do not cause me any problems.

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