05 Envoy 4.2L hesitates / rough

[jemmie]

I have an '05 Envoy 4.2L 4x4 with 130K miles on it and when cruising sometimes I can sense a little hesitation where RPMs drop ever so slightly. At idle, RPMs drop every few seconds and it's a little rough as well.

I just changed spark plugs (Delco) and cleaned throttle body yesterday. It fixed the problem a little but the vehicle still does it. Yes, I disconnected battery.

The coils were replaced at 120K with Evan Fischer coils.

What else should I be looking at?

Thanks.

 

[Tiggerr]

Vacumn leaks, O2 sensor, map sensor, lots of things could cause it. Does it always do it? Or only with the AC on at idle. Double check your coil boots/connections. Did you leave battery disconnected for 30 minutes? Any codes?

 

[jemmie]

I had the usual P0300, P0304, etc. codes intermittently.

What should I check on coil boots/connections? When I replaced plugs they look like they were in good condition - they should be as they only have 10K miles on them.

Battery was disconnected for about 1 hour.

O2 sensor is new.

I'll check out MAP sensor and vacuum.

I have not tested to see if it hesitates if A/C is off but will do that.

 

[DocBrown]

Which O2 sensor? There are 2 on the I6, upstream and downstream. A bad upstream O2 can cause the idle issues you are seeing even it if it's not throwing codes.

 

[cubano1992]

Minus the p300 codes your talking about jemmie I'm in similar boat as well. Ever almost stall out on you? What's your mpg been like? If our having the same issue as me i would like to see what fixes yours.

 

[jemmie]

I replaced the O2 sensor that's below the engine but in front of the cat.

I did starting fluid test for vacuum leak and didn't detect anything.

Yes, once every month or so the vehicle, while idling, would shut off. Every time I can start it right up again.

As for MPG, I get the same crap MPG I have had for years - 17 on the highway and 12-14 in the city. It blows but it doesn't blow any more than before.

I ordered a $10 MAP sensor and am going to swap that out to see what happens. I'm not hopeful but it's only $10.

It rough idles with the A/C off - just tried it.

 

[cubano1992]

Sounds o so familiar. Lol. I'm gonna do a vacuum leak test shortly. I have no cel light and that's wat confuses me

 

[gmcman]

P0404, pull the #4 coil and check for moisture. This coil is under the cowl drain on the hood seal and generally accumulates moisture. This is likely your misfire for that cylinder.

 

[jemmie]

I didn't see any moisture under #4 coil when I was changing the spark plug.

I ordered new air filter and am going to try that as well.

I poured in some Lucas Oil octane booster as another thread mentioned something about that.

I have also tried Techron, which has fixed codes and rough idling issues in the past.

 

[cubano1992]

Could the camshaft position sensor possibly be the culprit anyone? I mean if possible not to throw a code. But enough to make it run rough where you could just clean the screen on it. With everything jemmie has done as well as my self a friend of mine said to check that out.

 

[gmcman]

Was there surface rust inside the head where the plug sits under the #4 coil?

Did you try to gap the plugs? Sometimes this can lead to damage of the electrode.

 

[jemmie]

I did not see any rust where the plug sits under #4 coil. I did not try to gap the plugs.

I changed the MAP sensor ($9.69 from Amazon). I changed the air filter. I put in double dose of Techron.

The engine hesitates less now. Before, it would go down to 500RPM and almost stall. Now it stays around 600-650RPM. It still hesitates a little but is better than before.

Before I changed MAP sensor I got the P0300 code. Let's see if I get any codes now.

The problem has gotten significantly better since I started but I have done the following:

1) Cleaned throttle body
2) Changed spark plugs
3) Added four 12oz bottles of Techron
4) Changed air filter
5) Change MAP sensor

It seems like every action mitigated the problem from a lot (#1 and #2, done together) to a little. But the problem has not gone away. The problem was so bad before that I can sense it hesitating at highway speeds. Now I can only sense it at idle.

I'm going to leave it for now and see what happens. I'll update you all as this community has always been very helpful to me.

Thanks.

 

[jemmie]

I just went out and sprayed/cleaned the MAF sensor as well as maybe the K&N air filter I was using was leaking oil onto it. I doubt that's the problem though but I'm throwing the kitchen sink at it now.

 

[gmcman]

I don't think the MAF sensors have a great track record with filter oil. Honestly if that were mine I woukld ditch the K&N (I did) and go with the Green filter, Amsoil, or even the AC delco. The stock AC filter is rated one of the best but doesn't flow as much as the Amsoil or the Green.

Cleaning your TB will make a huge difference as you may have noted, just have to be sure you clean the edge of the butterfly completely.

Running a can of BG44K once or twice a year is good practice, but you seem to have already addressed that with the Techron.

I doubt the MAP sensor is your culprit, those just need to be checked with a vacuum tester and a multimeter.

Any reason why you changed your ignition coils? Just curious.

When you cleaned the throttle body, did you let it relearn the idle position? There is a sequence for that.

 

[jemmie]

I changed the coils because I was having continuous P030x codes. I changed one coil, swapped a couple, and said "F' it. Just change them all." The coils were $27 each. I don't even recall exactly what happened after that.

If by "relearn the idle position" you mean disconnect battery for an extended amount of time, then "yes". If you mean something else then "no".

 

[gmcman]

I would let the Techron work some more. Wouldn't hurt to check vacuum and you can pull the hose from the side of the throttle body facing the front of the motor.

Intake manifold bolts tend to get loose over time. I think the 05 has a fuel pressure test port near the fuel rail..not sure though.

 

[jemmie]

I'm starting to think it may be the new coils I installed. I didn't install AC Delco brand and instead used Evan Fischer. There are some reviews on Amazon that indicate they suck.

Anyone have any experience with them?

 

[Mooseman]

Evan who?

 

[gmcman]

I would check the vacuum, let us know what you find.

 

[NateDG]

When I cleaned my TB and changed my plugs today, I only pulled #10 & #28 fuses under the hood. I didn't wanna kill another HVAC motor.

Is there or is there not a definitive answer to whether that resets what ya need reset?

 

[Mooseman]

Yes it does.

 

[jemmie]

SOLVED! (I think)

I took it to my trusted mechanic for another issue (power steering cooler blew up) and spoke with him about this problem. He asked me what I had done thus far, I told him, and he said that's pretty much what they would do as well.

He then said maybe run a couple of bottles of Seafoam thru a tank of gas and see what happens. I told him I had done that. But that got me thinking about some posts I had read on other car forums about how that's mostly useless and you have to dump it in at the intake/throttle. So I bought one of the Seafoam bottles at Autozone with a spray. I used the entire bottle in one session and smoked up the entire neighborhood. But now the rough idling and hesitation appears to have completely gone away!

No, I'm not a Seafoam rep. But this is a case where *everything* else I tried didn't work, including Techron and Seafoam thru the gas tank. I suspect some other cleaners thru the throttle would have fixed the problem as well, but Seafoam definitely did the trick this time.

Thanks for everyone's help.

 

[Real McCoy]

Jemmie,
Can you tell me specifically where you sprayed the seafoam?
Into the throttle body?
into a vaccum port?
other?
Doug

 

[Blckshdw]

Jemmie,
Can you tell me specifically where you sprayed the seafoam?
Into the throttle body?
into a vaccum port?
other?
Doug

If you get the spray bottle with the straw, you spray it into the throttle body (past the butterfly plate obviously) If you go with the pour bottle, then you pour it into the vacuum hose at the brake booster.

 

[Real McCoy]

Thanks