Reduced Engine Power

[SarahFair]

I drive a 2006 Buick Rendezvous with 162,000 miles.

I bought it at an estate sale a few years ago with around 60k miles on it.
It was owned by an old lady who used it to get to and from her Dr's in Atl and around Oconee Co.

It's always had some issue or another, but about a year or two ago it started randomly shutting down while the car was idling.
It would give a rough idle then flash 'reduced engine power' and shut off.
Sometimes it'd start right back up, sometimes it took several minutes (not trying to turn over, just straight dead).

Then it quit doing it and everything would be fine.

A couple/few months go by, it'd start up again, then quit.

Sometimes it decides it wants to rev high and pull itself if you let off the break, but it randomly starts and stops that too.

Now, as of a couple weeks ago, it's started shutting off while I'm actually driving down the road.
I'll be accelerating around 50-60 mph and itll give the 'reduced engine power' warning, then shut off.
It'll do that maybe a couple days in a row, then everything is fine for a couple days.

The SO is infuriated with the car. He's replaced this and that over the years to try and fix it, just cleaned out the throttle body (again), and it's still doing it.
He said he's not investing anymore money in it..

Looking on the internet it's a common issue for this car and people have replaced almost everything imaginable on it to try and get it fixed to no avail..

I do have a car wash membership and noticed the other day after taking it to the car wash it started up. It acted up for 2 days, but today it seems fine.
I'm wondering if there isn't a loose wire somewhere, but I wouldn't know where to begin looking.

We are in the market for a new(used) SUV now, but aren't wanting to rush into anything, so Im trying to guide this one along til we find something.

Any advice on where to start looking for the issue?

 

[ryanh487]

Even though there's not a check engine light that you mentioned, have you gotten it checked for codes? The computer should store any trouble codes even if the light is off.

 

[notnksnemor]

Buick's in that era were known for throttle body issues that would do weird things.
Still have a 2004 Century that did strange things at about that mileage.

 

[baddave]

I'm a mechanic but not an auto mechanic. I just recently had a similar issue with my 93 4runner. After me and 5 others ( real mechanics) had given up I luckily ran across a man that collected 4runners. It was convenient to swap out parts to hone in on the issue. It was the computer. Someone that knows how to look at a printed ckt board can see that it had 2 leaky capacitors. This rocked on for over 1 yr and now I have my 4rynner back. Good luck. People are reluctant to go there bc its rare to have that issue

 

[SarahFair]

Even though there's not a check engine light that you mentioned, have you gotten it checked for codes? The computer should store any trouble codes even if the light is off.

Yes, my son has a connector that checks for codes.
The last thing we fixed right after this started back up was an ignition relay, that did not solve the issue.
He ran it over the weekend, I just asked him and he said it gave a P0449, which is a EVAP system issue.

 

[ryanh487]

Yes, my son has a connector that checks for codes.
The last thing we fixed right after this started back up was an ignition relay, that did not solve the issue.
He ran it over the weekend, I just asked him and he said it gave a P0449, which is a EVAP system issue.

Sounds like a faulty evap canister purge valve, which would cause the issues you're having. Have you replaced it yet?

 

[SarahFair]

Sounds like a faulty evap canister purge valve, which would cause the issues you're having. Have you replaced it yet?

Not yet, the SO has been working 14 hour days lately, so he hasn't been home in the daylight nor had a chance to even really research it (hence, the reason I'm here).

Looking at it videos, it doesn't seem all that complicated, so maybe I can get it changed out myself..

It's this piece with the blue connector, right?

 

[SarahFair]

Just got the SO on the phone, he said he's replaced the throttle body and the part I posted above, but he said he thinks there's something above the fuel tank

 

[westcobbdog]

I would sell the Buick for retail
if possible and review Clark Howard's strategy's for buying used and the best rated used cars by class or price. I am looking for my Son mostly on Auto Trader or Craigslist.

 

[ryanh487]

Just got the SO on the phone, he said he's replaced the throttle body and the part I posted above, but he said he thinks there's something above the fuel tank

There should be a purge solenoid in the fuel line near the intake manifold. If he's used to working on the vehicle he should be able to find it with a Google image search or YouTube tutorial.

 

[hopper]

I don't know alot about this stuff but check your hoses from evap canister all the way to the front. I was just about to switch mine on a 99 Jeep when I noticed the hose was disconnected. Plugged it in and it's been fine for yrs. Seems like your check engine light should be on but who knows.
If it's the computer you can reach out to this guy wranglerfix.com and ask if he knows anyone who will test run yours for issues. He has fixed many jeep computers and maybe able to point you to someone. Could be any number of sensors as well. Frustrating for sure.

 

[DAVE]

It is highly unlikely evaporative system fault is causing a no crank condition. I would be looking at the fuse / relay box under hood, try moving it around, pulling on wiring harness going into it to see if you can duplicate problem while sitting at home. The circuits inside that box will cause all kinds of intermittent problems, anything from no crank, no start, miss-fires, no headlights, on and on. I personally have replaced these boxes on 3 different 3.6 GM cars for all kinds of problems and finding the fault was no easy task but unless you can narrow it down, proofing through duplication, you might replace hundreds of dollars of parts and still be a no fix.

 

[Crakajak]

I had that same issue on my last ford truck.It was the mass air flow sensor going out.

 

[Oldstick]

Another possibility to check is the fuel pump and the line connections to/from the fuel pump. A small air leak there could possibly cause problems with starting or running. Sort of like when you get a defective soda straw that has a hole in it.

 

[Hillbilly stalker]

EGR valve ? They carbon up and stick from time to time. Run a can of Sea Foam engine treatment thru the tank. It helped my wifes Buick tremendously when the MPG fell way off. It will clean the whole system, maybe two cans , one in each tank at fill up.

An Evap problem will usually throw the dummy light on, a sign of Evap problems is the vehicle is hard to fuel up...the pump will keep kicking off. That doesn't usually affect the starting ability tho in my experience. My Silverado has a Evap cannister and piston located right in front of the gas tank, (another under the hood much like yours) a cracked hose or clogged cannister will trip the light. If its sucking air from a cracked line, it might very well show a "reduced engine power" code.

 

[Artfuldodger]

Your vehicle’s PCM may trigger the Reduced Engine Power Mode upon detecting a system failure. GM’s Reduced Power Mode can inhibit your vehicle’s ability to accelerate. Even if power isn’t reduced immediately, performance may be limited the next time you go to drive the car. In some instances, the PCM may actually cut off fuel delivery to the engine, rendering the vehicle undrivable.

When this happens, GM’s Engine Reduced Power Mode is being implemented as a “fail-safe” mode (also known as a “limp” mode).

You mentioned "Sometimes it decides it wants to rev high and pull itself if you let off the break, but it randomly starts and stops that too."

That may be a key on where to look. As others mentioned maybe somehow related to the throttle body controls. The electronic throttle actuator control (TAC) system.
In the TAC system, the PCM monitors two accelerator pedal position (APP) sensors to determine the driver’s desire for acceleration. Then, the device calculates the appropriate throttle response from a pair of throttle position (TP) sensors. Once the module has the necessary information from the sensors, the PCM uses an actuator motor (integrated into the throttle body) to operate the throttle, thereby controlling airflow into the engine.
A problem anywhere in the TAC system can easily trigger the Reduced Engine Power warning on the dash. For instance, the problem could be one (or both) of the APP sensors, which are usually integrated into the accelerator pedal.
The other primary input to the TAC system is a pair of TP sensors. When one (or both) of the sensors goes bad, the vehicle will enter Reduced Engine Power Mode.

There are many things that can put your car in "Limp" mode besides the TAC circuit.

 

[transfixer]

I don't know if that vehicle has a "drive by wire" throttle body ? or if its still a cable operated throttle body ? the symptoms you describe sound like drive by wire , if so the actuator that runs it is likely faulty, Chevy trucks were drive by wire in 07, and had numerous issues with the throttle bodies, depending on when that particular vehicle was made , ie either early 06 or late 06 model ? it may very well be drive by wire

If that is the issue it will need to be replaced, and also programmed by a scan tool capable of doing so before the new one will function.

 

[Crakajak]

I don't know if that vehicle has a "drive by wire" throttle body ? or if its still a cable operated throttle body ? the symptoms you describe sound like drive by wire , if so the actuator that runs it is likely faulty, Chevy trucks were drive by wire in 07, and had numerous issues with the throttle bodies, depending on when that particular vehicle was made , ie either early 06 or late 06 model ? it may very well be drive by wire

If that is the issue it will need to be replaced, and also programmed by a scan tool capable of doing so before the new one will function.

This makes sense.

 

[elfiii]

This makes sense.

Agree but getting into the parts swapping business gets expensive quick and you don't necessarily solve the problem.

 

[SarahFair]

Agree but getting into the parts swapping business gets expensive quick and you don't necessarily solve the problem.

Which is where we are at.
We've replaced a lot of parts already.
The SO is fed up with it right now, he doesn't even want to hear about it