2006 Impala LS down on power... maybe

DD#2 has a 2006 Impala that she loves.  It has maybe 65,000 on it and she's been driving it about 2 years.  3.5l V6 and GM's ubiquitous I-assume-4-speed ATX.

Lately she says it is down on power, to the point that she's nervous about driving on the freeway.  She has avoided almost any drop of automotive knowledge I've tried to impart, and the best she can tell me is that "the gas pedal doesn't work like it used to".  She seems to feel like she has to give it a notably more throttle than she used to to maintain speed.

I drove the car some when we first got it, and it drove like a big inexpensive American sedan should.  Cruising at 70 at about 1800 rpm, etc.  With the 3500 engine it is no powerhouse, but it certainly shouldn't make you nervous about driving it.  Her previous experiences with cars were a 1.8l / automatic Celica and a 3.3l Grand Caravan, so it's not like any of them were speed demons in comparison.

Since she's started talking about it, I have driven the Impala to work a few random days, and I'll be jigged if I can tell what she's talking about.  To me it still drives just like a big inexpensive American sedan.  It shifts fine, doesn't stumble, drives like a car that's designed to take it easy.  Unless it only does it when she drives, it's not doing anything I can detect.  I didn't drive the car for probably year in between, but I don't notice any change.  It's her daily, she could be right, and I just can't tell.

It has developed a small exhaust leak in / near the muffler.  Frankly, I suspect that she's hearing more engine noise than she used to, and she thinks it's laboring harder, when it is not.

It's taken her on several long road trips without trouble.  It apparently did have an incident a few months ago where it slipped out of gear and wouldn't go back in until she pulled over and restarted it.  At least that's what it sounds like from her description.  Transmission fluid is pink, full to the appropriate level, and doesn't smell burnt.

I don't think it has done the slip thing again.  But between that and her vague feeling that the gas pedal isn't working like it used to, she's nervous about driving it.  She still loves this big car, but she's lost trust in it.

So what do I do?  At 13 years old and 65k, do I throw a set of plugs in it and hope for the best?  The air filter has maybe 20,000 on it, so it's probably due.

Is there a MAF or TPS that needs to be cleaned or replaced?  So far this thing has exhibited some typical GM issues - evaporator solenoid, blend door actuator.  Is there a common GM issue that causes the car to run fine but be a little down on power?

Thanks!

I recently put an accelerator pedal in one. No codes? It pedal position sensors (2 of them in the pedal) could be reading differently than they used to, but they can't disagree too much without setting a code and the likelihood of them both 'drifting' by an equivalent amount is next to zero. 

Testing the full power of the engine is pretty easy. I've driven enough cars to know what a given hp/weight will more or less do. 3.5 Impalas actually feel kind of powerful to me, but in a goofy way.  It feels like a 3400 that magically got a real top end to its powerband, but since the tall gearing is the same you can only access those high rpms in 1st and 2nd at like 35-50mph and 70-95mph or so and 3rd gear high rpms are probably past the speed limiter. I would at least floor it through 1st gear and make sure it progresses normally. If you find it really laying over at high rpm it may have low fuel pressure: 'a little soft at normal rpm, and super friggin obvious at rpms i never go to'. 

Assessing part throttle torque at given rpms is a lot harder. If it feels ok to you, revs out normally and there are no stored codes i would just tell her to try to reset her expectations and keep driving it until she either forgets why she felt that way, or the problem becomes obvious enough to be diagnosed. 

Thanks for the input, and [seinfeld] I concur [/seinfeld] with your assessment of the normal power delivery.

I'll have to pull it up with the reader and see if it has any pending codes.  No CEL showing and it just passed the state's OBD-II plug-in check with no problems.

I'll drive it to work today, but last time I drove it, it took us down the freeway at 80 mph with no noticeable trouble.

OK, now I'm at work, 15 miles later, mix of traffic and freeway.

It seems to drive normally for me.  I put my foot down at 60 and it downshifted and ran up to 90+ without missing a beat.  It seemed normal in traffic, too.  It does shift all the way up even at 30 mph, so you may find yourself idling along at 950 rpm.  Maybe that's why she thinks it's going to die.

I put the reader on it and MIL is OFF for both main modules.  No pending codes.

The only potential oddity I saw was that the Absolute TPS was around 25% when I wasn't touching the pedal and the car was idling at 800 rpm (and not gusting more than about 10 rpm either way).  I don't know what the normal range is.  I didn't think to rev it and see what the sensor returned.

Clean the throttle body.  Reset computer with a battery disconnect and send it. Maybe throw a air filter at it...but 20k probably isn't that dirty.  A dirty throttle plate will cause slightly sluggish throttle response, and a higher throttle opening % than normal.  

TGMF said:

Clean the throttle body.  Reset computer with a battery disconnect and send it. Maybe throw a air filter at it...but 20k probably isn't that dirty.  A dirty throttle plate will cause slightly sluggish throttle response, and a higher throttle opening % than normal.  

OK, I'll give that a shot - thanks.  Is brake cleaner OK, or should I get carb spray?

I think I have a can of Seafoam around if I should go Full Smokescreen on the internals.

I use throttle plate cleaner on a clean rag, using my finger to wipe the bore and plate.  usually give it a couple focused sprays with the cleaner to areas I can't get with the rag and get rid of any smeared residue. 

I  would not spray brake clean in the intake, but applied to a rag and wiped is probably fine.

Maybe it was time for new plugs. 

The TB looks good but I will clean it anyway while I’m in there. 

It's probably the exhaust leak.  It's amazing, to a car person, how non car people percieve things sometimes.

My favorite are the "transmission not upshifting" issues that get bumped to me to look at, when the problem is that it has a wheel bearing growling so loud that it's all that you hear.  Wheel bearings don't upshift  And this is a fairly common thing, too, see it a couple times a year.

For another example, "brakes don't work" is often because the pedal is 1/2" lower than normal, and the driver is accustomed to the pedal moving THIS much to slow down, and they apparently use the brakes by pedal travel rather than pedal pressure.

Duke, you'll find that many of those 4T65E transmissions do really strange things from time to time.  My sister has an 05 and her son kept saying it was going into neutral and he had to rev it to get it to clunk back in.  Happened three times for him but we couldn't figure out why.

It's as if the PCM code writer was the stoner son of a GM exec who got the job "because dad."

Well, there are 2 issues that she has related in her head. 

One is the trans issue, which as far as I know happened once, with no repeats. 

The other is this vague feeling that she has to push her foot down harder than she thinks she used to. 

Somehow she has these 2 things conflated in her head that the car can’t be trusted. She constantly thinks it’s going quit, particularly at light throttle / low rpm. 

I’ve never experienced anything but normal operation with it. So today just to make sure, I replaced all 6 plugs and wires, cleaned the hell out of the throttle body, and the MAF sensor. The plugs were iridium and probably only have 30,000 miles on them, so that was pretty much an exercise in futility.

We’ll see if that makes any difference. 

My ex would consistently say that her 05 Scion sometimes just "didn't run right," so I would spend 30 minutes with the hood up in the garage smoking cigarettes and tinkering with another project after which she would say "It's much better, thanks."  

Having met you and your lovely SWMBO, I'm not saying she's gullible like my ex, just relating a story.  I would use a placebo to see if it was a real issue or if it was in her head.  She was a bit black-and-white on things.  She had a hard time understanding gray.

Keep us posted on progress.

Knurled. said:

It's probably the exhaust leak.  It's amazing, to a car person, how non car people percieve things sometimes.

 

My favorite are the "transmission not upshifting" issues that get bumped to me to look at, when the problem is that it has a wheel bearing growling so loud that it's all that you hear.  Wheel bearings don't upshift  And this is a fairly common thing, too, see it a couple times a year.

 

For another example, "brakes don't work" is often because the pedal is 1/2" lower than normal, and the driver is accustomed to the pedal moving THIS much to slow down, and they apparently use the brakes by pedal travel rather than pedal pressure.

The flip side of this is fascinating too.  Non-car people that drive the same car every day can have something (or many things) fail or wear out, but very slowly.  You hop in the car for the first time in a year and think "holy hell, how can you drive this??"

ProDarwin said:

Knurled. said:

It's probably the exhaust leak.  It's amazing, to a car person, how non car people percieve things sometimes.

 

My favorite are the "transmission not upshifting" issues that get bumped to me to look at, when the problem is that it has a wheel bearing growling so loud that it's all that you hear.  Wheel bearings don't upshift  And this is a fairly common thing, too, see it a couple times a year.

 

For another example, "brakes don't work" is often because the pedal is 1/2" lower than normal, and the driver is accustomed to the pedal moving THIS much to slow down, and they apparently use the brakes by pedal travel rather than pedal pressure.

The flip side of this is fascinating too.  Non-car people that drive the same car every day can have something (or many things) fail or wear out, but very slowly.  You hop in the car for the first time in a year and think "holy hell, how can you drive this??"

This reminds me of a transmission our shop did for a lady.  She grew up and lived in NYC so she never drove.  When she moved to TX, she got her license and bought this massive older S-class Merc.  It never shifted right, but she didn't know any better until someone told her it was bad.  When she brought it to us, it only had 2nd and 3rd.  We rebuilt it and got it perfect.

.... She sued us because now the car was "jerky."  We tried explaining (nicely) to her that she bought a crap car that never shifted right, and that "jerky" part is what we call "shifting properly."  We finally got her to shut up by taking her for a ride in our shop truck as well as my own Sonoma.  She finally gave into the fact that evidently, transmissions are supposed to have this crazy feature called "shifting."

OK, from the "no good deed goes unpunished" and "if it ain't broke don't berk with it" files:

This morning it set a P1107 code for barometric pressure circuit low voltage.  So I assume I berked up the intake sensor trying to clean it.

In reply to Duke :

IIRC there is no separate baro sensor, they look at the MAP when the engine is not running and use that as baro.   Gimme a little bit and I'll do some digging.

Did you unplug the MAP sensor?  GM connectors are generally only rated for four connections, and they tend to not even make it that far.  (Never unplug anything for the hell of it, in other words)  Circuit low would indicate that you're either losing the 5 volt reference (which can be caused by other failing sensors on that circuit..?) or it could indicate that it expect the manifold pressure to be higher KOEO.  Most likely the former, since GM is pretty good about discerning between "range/performance" and "circuit low/high".

According to my sources, P1107 is not something an '06 3.5 should be able to set.  Is it an '06? The underhood sticker will tell you the car's true model year, you can't go by production date or whatever model year is on the title.

My guess is that you can ignore the muffler hole.  If it were an exhaust manifold leak or a hole before the O2 sensor, then she might be right.  The sensor reads the extra oxygen and makes things richer.

In reply to Curtis :

Well, I was thinking the exhaust leak was more of a perceptual thing than a mechanical issue, since it would sound like it was working harder than before. 

Knurled. said:

According to my sources, P1107 is not something an '06 3.5 should be able to set.  Is it an '06? The underhood sticker will tell you the car's true model year, you can't go by production date or whatever model year is on the title.

My mistake, I pulled it again and it is actually P0107 - MAP / Baro Low Input. I cleared the code, fired it up, read the same code as pending, restarted the car, and within a minute it popped the CEL with teh same P0107.

Damn, I just ordered a MAF sensor for it while at work today.  Guess I'll be returning that.

I did not knowingly unplug or even go near the MAP, which is well downstream of the TB towards the accessories side of the engine, under a retainer.  Prior to cleaning, I physically removed the TB but did not disconnect it.  I did move the throttle plate around by hand, but not brutally.  As far as I know, no cleaner went into the intake manifold, and the cleaner should have all evaporated by the time I had it back together and fired it up.

I removed the MAF sensor (in its housing) from the intake path, and disconnected it.  I was careful to reconnect it and I just double checked that it seems secure.  I'll need to pop the engine cover off tomorrow and make sure I didn't disturb the MAP connector accidentally.

I had the + battery cable disconnected through all of this and did not reconnect it until I was all done.

Thanks for everybody's input.

What you need is a scan tool to see what the various sensors are reading.  Until you have that, you're just pissing into the wind.

Unless you had an OEM MAF on order, you'd be returning it anyway   I have had zero luck with any aftermarket MAFs.  OE or nothing.

Gimme a few minutes, I'm going to see if I see anything weird in the archives.

It's a Delphi MAF on the way.

Yeah, I'm just pulling the codes.  I'll hook it up tomorrow morning and see what the various sensors are showing.  Thanks again for your help.

Okay.  Now that it is acting up:  Get out your voltmeter and a paperclip and backprobe the MAP connector's five volt reference wire.  If you have a sewing needle/sewing nail, even better.  (Never probe the FRONT side of a connector unless you want to wreck the pins)  I forget if it is A or C in the connector, but it's the wire on the end that isn't ground.  Probably yellow/gray or something.  If both are ground, then go to the front of the engine and check the cam sensor wires near the power steering pump.  Rubthrough there is common and it shares the same 5 volt reference as the MAP.  Ground out the 5vref there and the MAP stops working.  So wiggle wires and pay attention to the voltmeter while doing so, to see if 5vref comes back.

If no amount of wiggling changes anything, then it's time to start unplugging other sensors.  I remember in the slightly older days, failing EGR valves could take out the whole 5 volt line.

A "signal low" failure means that the signal return going to the PCM is lower than .5v.  Generally that only happens if the sensor itself is bad or the signal return or 5vref wires are grounded.  (There is a bias voltage on the signal return, so the PCM will be able to detect an open circuit)  More than likely, something is taking out the 5vref.