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Greg A
Greg A, Master Troubleshooter
Category: Pontiac
Satisfied Customers: 6128
Experience:  Working with Electronics & Cars for 25+ Years
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Pontiac montana: intermittent..park it idles at around 1400 rpm..TPS

Customer Question

Pontiac montana 2001-Idling at high speed after being started.While driving,it will hold a speed of 65 km beacause of engine speed,problem is intermittent. If I turn off the motor and restart most of the times it will idle back to normal 680 rpm for a short period.
In park it idles at around 1400 rpm, I get a TPS reading of 3 % from the OBDD port should it not be at 0 % ?,the trottle plate is closed. What should I look for ?
Submitted: 5 years ago.
Category: Pontiac
Expert:  Greg A replied 5 years ago.

Hello & Welcome,

 

It sounds like you have a scan tool that shows you the data readings from the system - that is good.

 

I believe the TPS reading should be zero if you are not on the throttle. I would check the connections to the Throttle Position Sensor, and while I was at it, take a good look at the throttle body and see if there is any dirt or buildup in there. This could be causing the throttle to stick and give you this issue. You might also want to check for buildup around the Idle Air Control (IAC) valve too.

 

I hope this helps. Please let me know what you find.

 

Take Care, Greg A.

Customer: replied 5 years ago.

THANKS FOR THE REPLY GREG, WIRES FROM THE TPS TO PCM WHERE CHECKED BY THE DEALER, 5 WIRES WHERE DAMAGED IN THE HARNESS NEAR THE PCM, SOME WIRES WHERE BARE AND HAD STARTED TO CORRODE. THEY WHERE FIXED, TECH. WAS SURE THAT THE PROBLEM CAME FROM THIS SITUATION. CAR WAS TESTED AND WAS IDLING PROPERLY.

ON MY WAY HOME THE TROUBLE CAME BACK 5 MINUTES AFTER I HAD LEFT FROM THE DEALER.

THE NEXT DAY THE PROBLEM WAS THERE ALL DAY. TODAY IT IDLED OK , THE DIFFERENCE BETWEEN THE 2 DAYS IS OUTSIDE TEMPERATURE

TODAY WAS A COOL DAY HERE IN MONTREAL.

 

THIS PROBLEM OCCURED FOR THE FIRST TIME IN OCTOBER 2008 DISSAPEARED DURING WINTER AND CAME BACK THIS SPRING.

 

THE WIRES WAS A VERY LOGIC DEDUCTION , WHAT ELSE COULD GIVE A FALSE TPS READING TO THE COMPUTER I SUPPOSE THE PCM REACTS TO THIS FALSE READING BY INCREASING RPM TROUGH THE IAC ?

 

TECH SAID THAT HE HAS TESTED THE TPS SENSOR AND THAT IT TESTS OK

 

I HAVE AN ENGINE PERFORMANCE MONITOR CALLED CAR CHIP PRO IT CONNECTS TO THE OBDII PORT I CAN MONITOR TPS POSITION IN %

 

 

Expert:  Greg A replied 5 years ago.

Hi again,

 

It sounds like they were close, but didn't get the problem fixed just right. And the fact that it seems to happen in warmer weather and go away in the cold would tend to confirm a loose connect of some kind (things expand in heat and contract in cold).

 

If it was me, and it was possible, I would have turned around and went right back to the dealer, but that is just me.

 

Since the tech said that the TPS was OK, then I would suspect something in the wiring back to the PCM. Any bad connection along that line would have the same effect.

 

Yeah - I like the "toys" that show the data too. I have a system that connects to my laptop, that I can use at home, to gather data. I will sometimes log the data and import it into a spreadsheet, and then do some graphing on the data.

 

If you would like, I can probably find the point where those sensor signals enter the PCM and you can try wiggling those wires to see if the TPS reading changes. Just let me know and I will see what I can do.

 

Thanks, XXXXX

Greg A, Master Troubleshooter
Category: Pontiac
Satisfied Customers: 6128
Experience: Working with Electronics & Cars for 25+ Years
Greg A and 8 other Pontiac Specialists are ready to help you
Customer: replied 5 years ago.

I DID GO BACK AFTER LUNCH BUT THE TECH HAD JUST LEFT ON VACATION AND THE DEALER REP WANTS ME TO SEE THE SAME TECH THAT STARTED ON MY CAR.

 

HE HAD THE WIRE HARNESS OPEN AND THE PCM UNPLUGDED

 

I WOULD APPRECIATE KNOWING WHERE THOSE WIRES ENTER THE PCM

 

WHEN THE TROTTLE PLATE IS CLOSED (FEET OFF THE TROTTLE)WHAT IS THE VOLTAGE SENT TO THE PCM 5 OR 0 VOLT

 

I MONITERED THE TPS FOR 5 MIN AND ON THE GRAPH THE LINE IS FLAT AT 3% WITH NO VARIATION THE TPS IS SAMPLED EVERY SECOND IF IT WAS NOISE OR OXIDATION WOULD IT NOT VARY ON THE GRAPH

 

IREALY WOUL LIKE TO FIND THAT TROUBLE

Customer: replied 5 years ago.

I DID GO BACK AFTER LUNCH BUT THE TECH HAD JUST LEFT ON VACATION AND THE DEALER REP WANTS ME TO SEE THE SAME TECH THAT STARTED ON MY CAR.

 

HE HAD THE WIRE HARNESS OPEN AND THE PCM UNPLUGDED

 

I WOULD APPRECIATE KNOWING WHERE THOSE WIRES ENTER THE PCM

 

WHEN THE TROTTLE PLATE IS CLOSED (FEET OFF THE TROTTLE)WHAT IS THE VOLTAGE SENT TO THE PCM 5 OR 0 VOLT

 

I MONITERED THE TPS FOR 5 MIN AND ON THE GRAPH THE LINE IS FLAT AT 3% WITH NO VARIATION THE TPS IS SAMPLED EVERY SECOND IF IT WAS NOISE OR OXIDATION WOULD IT NOT VARY ON THE GRAPH

 

IREALY WOULD LIKE TO FIND THAT TROUBLE

Expert:  Greg A replied 5 years ago.

Hi again & thanks for the accept.

 

Here is the schematic that shows what pins and wiring is connected between the TPS and the PCM. I will see if I can get you a diagram of the PCM connectors.

 

The "C2" & "C1" references on the right of the signals refer to the connector numbers. The pin numbers (in those connectors) are on the left of the signals.

 

graphic

Expert:  Greg A replied 5 years ago.

Hi again,

 

Here is a PDF file that shows all of the signals on the PCM Connectors <-Click to view.

 

Here are larger diagrams of the connectors (the ones in the file are kind of hard to read).

 

graphic

 

graphic

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