Low power and sticking transmission?

Tiny
RYDER1477
  • MEMBER
  • 2004 CHEVROLET IMPALA
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 188,000 MILES
My car listed above LS 3.8L is super low on power. When going uphill, the transmission doesn't kick down to grab a lower gear (it does once in a while) it has hardly any passing power on level ground, and just the other day after barely making it up a clear dry road, it was stuck on high RPMs. I don't know what to make of it. This came just one week after I had zero warning lights for the first time since I owned this car. Any thoughts of what to check?
Sunday, March 2nd, 2025 AT 2:30 PM

14 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
It sounds like you have a weak fuel pump, jumped timing chain or a clogged air filter. We should run the codes though even though the check engine light is not on.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If there are no codes let's check the compression on the engine and check the fuel pressure.

https://www.2carpros.com/articles/how-to-test-engine-compression

and

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Fuel Pressure (Key ON Engine OFF) .................... 364-405 kPa (53-59 psi)

Check out the images (below). Please let us know what happens.
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Monday, March 3rd, 2025 AT 11:02 AM
Tiny
RYDER1477
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I did your recommended course of action, but the problem persists.
I apologize for not leaving an update.
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Monday, March 31st, 2025 AT 1:48 PM
Tiny
KEN L
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What all did you do? Codes?
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Tuesday, April 1st, 2025 AT 8:53 AM
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
I checked the fuel pressure and it was 55 psi. So I l moved on to the timing and it was spot on as well. The only code I got after that was P0122. Throttle position/Switch A circuit low.
I didnt test it but just replaced it and still the problem persists. Same code, only now the car surges when parked and running and/or doing highway speeds and then seemingly power drops. Floor the gas pedal and it sounds like its being flooded. This car has been a nightmare for me.
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Wednesday, April 2nd, 2025 AT 11:49 AM
Tiny
KEN L
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So to be clear you replaced the sensor below? Also, "circuit low" can be the sensor is not adjusted correctly.

P0122 - Throttle Position Sensor/Switch "A" Circuit Low Input

How does the electrical connector look? A poor connection at the sensor can cause this as well. Check out the images (below).
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Thursday, April 3rd, 2025 AT 9:18 AM
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
  • 2004 CHEVROLET IMPALA
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 192,400 MILES
I'll describe it as best I can. My car listed above LS has had engine, drivetrain and emission problems since I've had it. But now, it seems to be getting worse. I'm cruising along doing 120 kph and then the engine will start to jerk like its losing power. And it is because I will floor it, and it'll barely keep speed at 80 kph. And then it really slows down. So, I feather the gas, sometimes it helps but today it didn't. It sounds and feels like it's being flooded. I don't know how or if that helps at all but that's how it feels to me. I recently thought I had solved the cylinder 4 misfire problem as the code was no longer there when I last checked on my OBD scanner. In fact, there were no codes for the 1st time ever, but the engine light is still there. So, idk.I got a new camshaft position sensor as I read it could be that all the symptoms are exactly what my car is doing. Where is the camshaft sensor on a 3.8L? I thought by the water pump pulley but I can't see it anywhere.
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Do you have ay response for the last two questions we answered?
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
Yes, there are responses now.I apologize.
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
Am I still getting an answer for this question?
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
KEN L
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Yes, so the check engine light is on but no codes, correct? When this happens the PCM can be bad, I would send it in for testing. I have also seen the catalytic converter get clogged up and cause this issue as well. Some inexpensive code readers will not pick up all of the codes FYI. The Camshaft sensor is near the rear of the engine at the top behind the intake manifold. Check out the images (below). Let us know how it goes.
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+1
Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
Well no I do have codes. I should of put that in there. They are :
- P0036 >> HO2S HEATER CONTROL Circuit bank 1 Sens 2
- P0122 >> Throttle position/Switch A circuit low
- P0134 >> O2SENS NO ACTIVITY DETECT Bank1 Sens 1
- P0135 >> O2SENS HEATER circuit bank 1 sensor 1
I had thought I fixed all of these as there were no codes last I checked last week. Then all a sudden, this power loss probelm happened, checked again and yesterday these codes were there.
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
RYDER1477
  • MEMBER
  • 44 POSTS
ALso, my engine is a 3.8L. Would the camshaft position sensor be in the same approximate spot?
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Sorry about that, no the camshaft sensor is at the front of the engine down low on the 3.8 liter engine. I would replace both oxygen sensors on the bank 1.

This guide can help walk you through it:

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

Here is the throttle position sensor location so you can swap it out as well, but I must say if all of these codes came up at once you may have a bad PCM. Check out the images (below). Let us know how it goes.

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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)
Tiny
RYDER1477
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I changed out the throttle position sensor like a month ago. Im having trouble just locating the camshaft position sensor. I even took off the passenger side tire and lifted it up and still couldnt see it. Is it behind a pulley or something? Also, are all O2 sensors heated? Because I just replaced the downstream sensor a cpl weeks ago but I dont think its a heated sensor. As soon as I replaced it and ran the codes I got the -
P0036 HO2S HEATER CONTROL Circuit bank 1 Sens 2
P0134 O2SENS NO ACTIVITY DETECT Bank1 Sens 1
P0135 O2SENS HEATER circuit bank 1 sensor 1
I just ran it again and same codes are there. P0036 has been there since Ive owned this car.
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Thursday, April 3rd, 2025 AT 9:30 AM (Merged)

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