Poor idle and low speed performance

[drvnkd]

I'm pretty sure this is my first post, but I have been trolling the boards since obtaining my 05 envoy just over a year ago.
I got a great deal as it was my old mans truck and only had 35,000 miles on it.

I am a bit disappointed with it though as it always seems to have some issue or another.

For the past few months, it has been a bit of a rough idle and surge while releasing the brake and just creeping forward.
At stop lights when I lift up a bit to go .5 mph or so you can feel a stutter of sorts. Once in a while it will surge a bit. up to 1k rpm at least.
I figured the TB was dirty and just being a PITA at near no opening.

I was getting ~9.6 mpg with the winter gas.
I finally took the time to clean up the TB and replaced the plugs with 41-103's.

The TB was filthy.

Now It's clean

Old plugs looked like this one.

I have no idea why the ground electrodes are at an angle, but they were all the same, so I'm guessing they came that way.


My reward for the clean up was ~8.6 mpg.
The response is better at the very low end, but it still has the stop light stutter.
I'm also driving it like a little old man to try and get better mileage. 10 mpg or worse has had a terrible effect on my driving
A gallon per day to commute has been driving me crazy. Although, I did start riding a bicycle to work over the summer. (~10 miles round trip)


I have had a few CEL's pop up and go away by on their own. One was for the air blower/ check valve malfunction.
I'm not sure if that was just a connection I may not have seated properly when replacing the fuel level sensor.
I hear it on cold starts and then it shuts off. I never did investigate the check valve further as the code cleared.

Another code that has come and gone on it's own was a low coolant temp. I plan on connecting a code scanner to see if I can monitor the coolant temp after some more trolling here

I will also pull the CPAS and see what kind of shape it's in, but it has never thrown that code.

Another annoyance I have is that on cold starts, the exhaust stinks like it runs really really rich. It gets better, but I think it always runs rich and smells worse than it should.


I'm wondering if there are any other thoughts on things I can check or should expect to go fail sooner than later.

The problems so far seem all too common when surfing the interwebs.

in 38,000 miles it has had:
2 sets of brakes
Both front wheel bearings
Fuel level sensor (DIY'd - thanks forum supporters)
AC compressor is shot. Sounded like a rod was going to bust through the block, but I used the smaller serpentine belt as I'm a cheap bastard (thanks again forum supporters)
1 HVAC blower control module (warranty)
Module just failed again and I ordered the FET (Thanks Roadie)
It's also got a nice squeal from the passenger side rear brake, but looking at the rotors, they clearly have not been used in a long time.


It is entirely possible I have something hanging up in the brakes, but that should not cause the stoplight stutter.

Thanks for any insight

 

[triz]

For one this truck seems like it has not had the best maintenance. I've never seen a throttle body that dirty. I would after cleaning the throttle body, change your fuel filter. Clean your MAP sensor, check and replace your air filter. Run a tank of Premium Shell gasoline along with a bottle of Amsoil Performance Improver or Chevron Techron. Off the shelf the Techron is a great product and it works. Finally switch to Amsoil XL for your oil. It's another great product. Since my truck has been on it I've gained however slight 1 to 2 extra mpgs. Then when that basic stuff is out the way look at your other fluids. DIFF. transmission, transfer case. Disconnect the battery as well to have the the truck relearn.

Also just saw the part about your brakes. If you have something dragging on your disc or a bad caliper that can severely kill your mpg. Get it checked before anything else.

 

[Playsinsnow]

Check for dragging brakes, run a few bottle of Chevron Techron, and I know it sounds elementary, but check the tire psi. It can drop as ~1 psi every 10F drop. I can imagine it has been cold there recently, I am constantly checking to keep my tires in good condition. Also, change your driving habits and go s l o w e r. I mean keep that tach under 2k and see what kind of mileage you get. It is slow but why wouldn't you try to drive slower if you have bad mpgs? I have seen really cold city mpgs around 10 before. And I can get 15 city no problem if it's above 20*F

 

[CaptainXL]

Another code that has come and gone on it's own was a low coolant temp. I plan on connecting a code scanner to see if I can monitor the coolant temp after some more trolling here

This statement stood out more than everything else you said.

If the code for low coolant temp came and went...even once...that is enough. I recommend you stop with your other maintenance for now and change the thermostat and coolant. ASAP

A bad thermostat will cause horrible mileage and a possible plugged catalytic converter. Not to mention other possible symptoms.

 

[Chickenhawk]

I second that, and suggest you do an exhaust backpressure check.

It sounds suspiciously like your cat is plugged.

Can you take a picture of your coolant temp gauge when it is warmed up for us.

 

[Matt]

change your fuel filter.

05 truck, fuel filter is in the tank and N/S.

 

[drvnkd]

I plugged in the scan tool on my way home from work and could not get the temp above 182F.
This morning, I let it warm up for 5 minutes or so and the highest ECT was 185.

My commute is less than 15 minutes, so I have no idea if it reached full operating temp. It's only 35F outside.
The temp in buffalo changes a lot. 50 one day and 5 the next. I figured that was part of the problem.

I do not know what the threshold for the CEL is, but the P0128 was stored. I think thats what it was. low coolant temp.
As for the gage on the dash, it's nearly two tics left of the center 200.

If memory serves, it has always on center/200
I found a dash pic from last June and the dash was almost right on 200. (back when I changed the fuel level sensor)


As for maintenance, I always run Mobile 1 5w30 in my cars and changed it when the oil life meter suggested and run several bottles of fuel system cleaner.
Some Techron, some lucas at least one STP something or other.

My tires are up to pressure. I do keep an eye on them as the old tires used to lose pressure at the rim. My tire guy did a pretty good job sealing the new tires up on the corroded and now ugly rims.


When the truck was my dads, he too had a short commute, but he LOVED his remote start and would warm it up/cool it down every time it was
hot or cold outside. I figured that is why it was so dirty, but I don't know where that grime really comes from.

I'm pretty sure the other fluids were not changed. Looks like I'll start with the coolant, then trans and eventually diff. I hate diff fluid changes.
Last time I tried to check the trans fluid, the dip stick broke off at the plastic cap. I snagged one from a junk yard, but I don't know if it's the correct length
as it was in a slightly different location under the hood.

These items will take some time as it's cold outside and I am for too cheap to pay reputable mechanics for service work.
As for the rear wheel noise, it would squeal when I turned left OR hit the brakes. I will investigate the next time it gets to 45-50 deg
That problem was there before my TB cleanup and spark plug change. After two 5 mile trips on the highway i'm up to 9.1 mpg


Are there any other tests for a restrictive cat that are DIY friendly? Pressure gage in an O2 Port?

 

[The_Roadie]

... highest ECT was 185.... nearly two tics left of the center 200.

Huge clue. Thermostat and sensor both suspect.

.. I don't know where that grime really comes from.

No PCV valve on the I6. Crankcase fumes blow back to the backside of the butterfly disk and coat it like it's a 1835-vintage spittoon in Dodge City. GM saved a dime, and doomed us all to continuous throttle body cleanings.

I'm pretty sure the other fluids were not changed.

Are you 4WD? If so, the transfer case is vitally important to change regularly.

..I am for too cheap to pay reputable mechanics for service work.

The fuel you wasted by having low coolant temp, and the risk to your cat ($$$), would have paid for a mechanic possibly multiple times over. Misplaced frugality can be a curse, not a virtue.

 

[drvnkd]

No PCV valve on the I6. Crankcase fumes blow back to the backside of the butterfly disk and coat it like it's a 1835-vintage spittoon in Dodge City. GM saved a dime, and doomed us all to continuous throttle body cleanings

Sounds about right.

Are you 4WD? If so, the transfer case is vitally important to change regularly.

Moved up the list.

The fuel you wasted by having low coolant temp, and the risk to your cat ($$$), would have paid for a mechanic possibly multiple times over.

True, but the light disappeared a day or two after getting the code read. Mileage has never been good and it coincided with the switchover to winter blends and freezing temperatures.

It was the sudden decrease after actually taking action to freshen things up that annoyed me. More research leads me to the discovery of more issues.

 

[CaptainXL]

True, but the light disappeared a day or two after getting the code read

Usually this is the case. The CEL doesn't come on until things start to get really bad. Like when the coolant is in the 180's. At this temp the PCM will continually attempt to enrich the mixture which will can create a runaway situation the PCM can't control. Not to mention a dirtier crank case, the need for more oil changing, sticking valves, dirty/fowled plugs and injectors.

Not to mention the engine has more than likely been running like this for thousands of miles. Just killing the engine and exhaust.

Not trying to scare you but I don't think you are fully grasping the severity of your situation.

Do what we said earlier ( change thermostat and check exhaust back pressure) and then proceed from there.

 

[drvnkd]

Huge clue. Thermostat and sensor both suspect.No PCV valve on the I6. Crankcase fumes blow back to the backside of the butterfly disk and coat it like it's a 1835-vintage spittoon in Dodge City. GM saved a dime, and doomed us all to continuous throttle body cleanings.Are you 4WD? If so, the transfer case is vitally important to change regularly.The fuel you wasted by having low coolant temp, and the risk to your cat ($$$), would have paid for a mechanic possibly multiple times over. Misplaced frugality can be a curse, not a virtue.

Usually this is the case. The CEL doesn't come on until things start to get really bad. Like when the coolant is in the 180's. At this temp the PCM will continually attempt to enrich the mixture which will can create a runaway situation the PCM can't control. Not to mention a dirtier crank case, the need for more oil changing, sticking valves, dirty/fowled plugs and injectors.

Not to mention the engine has more than likely been running like this for thousands of miles. Just killing the engine and exhaust.

Not trying to scare you but I don't think you are fully grasping the severity of your situation.

Do what we said earlier ( change thermostat and check exhaust back pressure) and then proceed from there.

I will plan to change it out tonight or tomorrow

Edit: Scratch that. Thursday at the earliest. Advance, Napa, Autozone do not have the AC Delco parts. Amazon wins.

 

[Chickenhawk]

Also, change your coolant temp sensor as well as thermostat. It is difficult to tell for certain which one isn't working and the end result is exactly the same, so you might as well do both. They are side-by-side.

Your priorities should be the thermostat, coolant temp sensor and coolant. Then the transfer case fluid. Then start worrying about the other fluids

Exhaust backpressure tests can usually be done inexpensively at muffler shops because they want to sell you a new cat. PSI should read near 0 at idle and no more than 1 or 2 PSI at 2500 RPM. You can also buy your own exhasut backpressure gauge. Also pick up a new front oxygen sensor, then cut the wire to the old one and use a normal deep socket to remove it so you can get the backpressure gauge in there. (It will likely be seized in the manifold.)

Once you have checked your backpressure, write down your two readings and let us know. Then use a special oxygen sensor socket to put the new one in.

It is very likely your cat is plugged, by the way.

 

[drvnkd]

Thanks.

I ordered both the sensor and thermostat.
I'll hunt around for a nice 0-5 psi pressure gauge and see if I can hack something together.

It's not completely shot, unless the O2 sensors and ECU behave like the coolant temp and do not actually
give you a proper warning or indication?

I'm going to agree that it has probably been faulty for a while. On a trip to the parts store yesterday the temp needle is only one tick left of 210.
I would not think anything at all of a 10-20 deg F deviation. (the parts were not even for my truck )

On a side note, I also need rear brakes. The outboard pad on the passenger side is down to the metal tabs while the inboard pad has much more material.
Not to mention that the disc's look terrible in terms of wear pattern.

 

[Chickenhawk]

One thing to remember about cats (and everything mechanical in general) is that codes are generated for emissions problems. There are no trouble codes when parts are failing that do not affect emissions. (One person on the other site got mad that he had no codes for when his alternator was failing, and sadly there is no one there left any more to tell him otherwise.)

So if a cat has gone bad in that it doesn't clean the exhaust, the rear oxygen sensor will start to match the front oxygen sensor and it generate a code. But if the cat is plugged, it technically still works. Your truck doesn't run well and especially has trouble accelerating on the highway, but what little exhaust gets through, is still cleaned properly.

Therefore, your cat can be completely plugged and it still may not generate a code. We have seen some VERY plugged cats in here.

We will also be seeing more and more as the vehicles age because modern cats require a very narrow range of mixture and even something as simple as a misfire on the highway for a few minutes can toast them.

Long term running cool because of a defective thermostat or coolant temp sensor is the absolute number one leading cause of cat problems in this forum.

It's almost a signature line for us:
#1 - Clean your throttle body.
#2 - The red wire is supposed to be disconnected. It provides 12V to a trailer if required.
#3 - If your coolant temp gauge is running two ticks or more to the left, you will need to change your thermostat and/or coolant temp sensor.
#4 - Change transfer case fluid every 50,000 miles.
#5 - Trust The Roadie.

 

[drvnkd]

The ironing is I came here because of my HVAC...
It was my rant that drove to more serious business.

I was talking with a guy at work about his envoy. Turns or he just had his thermostat repaved when his fuel mileage dropped off. He gets 21 mpg Highway. Now I won't talk to him.

 

[The_Roadie]

#5 - Trust The Roadie.

 

[IllogicTC]

I always imagined that more like a turbo gauge.

 

[drvnkd]

Are you sure it's full?
In two or three more posts it will probably drop to E and you will be stranded somewhere on the internet.