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2002 PT motor surging

 
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Old 31 Aug 2007, 10:51 pm
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Default 2002 PT motor surging

the motor surges at anytime with or w/o speed control going down hill and on flat. This happens around 45-65 mi/hr. Has happened since 40,000 mi. now has 110,000. Service dept. cannot find cause. They changed O2 sensors this week, no help. When I take foot of gas and then accelerate it surges constantly. Help me!! Very frustrated
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Old 31 Aug 2007, 11:30 pm
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Default Re: 2002 PT motor surging

Anyone check the TPS, throttle position sensor?
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Old 01 Sep 2007, 07:37 am
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Default Re: 2002 PT motor surging

Mean Green has a good suggestion with the TPS. I checked around the DIY postings for surging and found this....

I have a 2001 TE PT with 32k miles and automatic transmission. When driving on interstate highways at speeds over 55 mph (I usually set the cruise control at 68 mph in the 65 zones), when on flat terrain the rpm's will suddenly increase from 2800 to 3000, for about 10 to 15 seconds, then drop back down. When going up hills, I understand this is normal. But why am I getting the rpm increase/downshift on completely level surfaces at these speeds? The A/C is not turned on during these occurrences. Thank you. - Peter, from Wisconsin.

ANSWER
It may be your torque converter solenoid unlocking. This would cause an increase in rpm without an actual downshift into a lower gear. Anytime you touch the brake or gas the solenoid will unlock the converter. This may be normal, or there may be something causing the converter to unlock. Only a scanner datastream can record the function of the lockup solenoid.

...and another one

I have a 2002 LE PT Cruiser with a manual transmission. It has less than 1,500 miles on it. I've noticed a peculiar idle hunting/surging problem that the dealer either can't fix or claims that it is normal. This problem becomes worse after the car is fully warmed up and heat soaked. Here are a few of the symptoms of the problem. I believe that they are all related.

As you are coming to a stop from any speed, you put in the clutch and finish the stopping in a coast mode; the engine speed will drop down to about 1,000 rpm and then increase to 1,300 rpm or as far as 2,000 rpm. Sometimes it will drop to 1,000 rpm, go back to a higher rpm; then repeat the cycle another two or three times. Once you've come to a complete stop, the idle will settle down at its normal 800 rpm. Even after the surging cycle, the idle will not drop below 1,000 rpm until the wheels have stopped turning. This happens whether the clutch is disengaged or not, and it doesn't matter if the gear selector is in a gear or in neutral.

Another symptom happens when you are either creeping along in a traffic queue or moving through a parking lot. You give it just enough gas to move 10 feet while letting the clutch out, you let off of the gas to roll the 10 feet, and then the engine will zoom up to at least 2,000 rpm before dropping back down to 1,000 rpm. This symptom is really annoying while parking because the engine is revving up every time you have to move to maneuver into a parking spot.

A related symptom happens when you shift early between gears at engine speeds below 2,000 rpm. After you let off the gas and put in the clutch to shift to the next higher gear, the engine speed will increase 300 to 700 rpm before decreasing. This makes shifting smoothly difficult because you can't match engine speed to transmission gear speed easily.

An interesting side note is that you can't stall the engine if the car is rolling. At a complete stop, you can let out the clutch and the engine will stall. But if you have the car moving just a little, you can let out the clutch and it will accelerate to 10 mph in first. You can then up shift without using the gas pedal and the car will hold 25 mph in fourth. I've never had manual transmission car that acts like an automatic before.

The only Chrysler dealership that attempted a fix performed a flash update control of the PCM. This was based upon a TSB. The work order didn't indicate which one, but I think it may be TSB #1802701. Unfortunately, since the update, the problem seems to be worse. Any advice, ideas, or suggestions would be appreciated. - Kevin, from New Mexico.

ANSWER
Engine rpm is controlled mostly by the input from the MAP sensor. The IAT, O2, ECT, etc. all contribute to controlling the rpm, but the MAP is the boss. DC does not use a mass air flow meter like other makers. They rely solely on the MAP signal to calculate the PCM outputs. I would look closely at the signal. It may be within specs, but just barely. Mopar is known for failing MAP sensors.
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Last edited by CREWZIN; 01 Sep 2007 at 07:40 am.
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