GMC Envoy 2003 Engine Shake and Rough Idle.

[mqayyum]

I bought my Envoy 2003 XL SLT 4.2L just in Dec 2011 and performed necessary maintenance which included replacement of all breaks, Engine Synthetic Oil/Filter, AC Delco Spark Plugs, Transmission Oil/Filter and Fuel Filter and cleaned Throttle body, Replace Ignition Coil # 1, Cam Actuator, Engine Side O2 Sensor and CAT. In addition to this I have performed Fuel Injector cleaning by One Stop service Center upon recommendation of GM Mechanic who notices pinging on Fuel Injectors.

I am noticing engine shake at the time of engine start and stop (Switch off). In addition to this I have rough idle problem when accelerate or stop at signal light. RPM fluctuate from 615 to 300 and back within 2 second. It does not matter whether is cold or warm start. sometime it is hard running on first gear and sometime it seems smooth. SES light is also on.

I have been searching and found some articles which indicated that either the Motor mount need to be replaced or Plugs with NGK ILTRB11 (3474).

Last month I just opened first three Plugs and I found carbon fouled. If this is a problem then can you advise me what to do next.


Thanks a lot for your assistance in advance.

Qayyum

 

[The_Roadie]

Welcome!

As long as you disconnected your battery to clean the throttle body (front and back side) then your issue may be something else.

First, we need the code that's causing the SES light to be on.

Only use Delco 41-103 plugs.

Motor mounts are a cause of a vibration (10 Hz) at idle that is worse in DRIVE than in PARK or NEUTRAL. Bad motor mounts cannot cause the idle RPM to move so that you can see it on the tachometer.

Why did you change the cat? Was it plugged? How many miles on the vehicle? Why did you change one coil?

Carbon fouling is a bad sign - if the cylinders have carbon build-up, the shaking at engine stop may be dieseling - unwanted ignition from hot spots on the carbon. You may also want to get the compression checked. That can also cause misfires - I'm guessing your code is a a misfire code (PO30X) where "X" can be any number from 0-6.

Are you 4WD? If so, the transfer case fluid also needs to be changed every 50K miles, which is a surprisingly short interval. Nothing to do with your problems today, but I always mention it in case new members haven't read the Owner's Manual yet.

 

[mqayyum]

First of thanks a lot roadie for your quick response.

Welcome!

As long as you disconnected your battery to clean the throttle body (front and back side) then your issue may be something else.

Yes it is true. I have cleaned at least twice by removing the whole TB with battery disconnected.

First, we need the code that's causing the SES light to be on.

I will have to visit the nearest service center soon to see the SES code. previously it was P0442 and P0420.

Only use Delco 41-103 plugs.

Noted. I will buy these plugs but I am not sure if this will solve the problem. I have decided to change the plugs only because of Carbon.

Motor mounts are a cause of a vibration (10 Hz) at idle that is worse in DRIVE than in PARK or NEUTRAL. Bad motor mounts cannot cause the idle RPM to move so that you can see it on the tachometer.

As mentioned earlier post the engine is shaking at the time of start and stop. I also observed slight vibration while driving specially when AC is on. Although one thing is very clear. When AC is on the rough idle is less like it drop only from 615 to 500 RPM and back within a second.

Why did you change the cat? Was it plugged? How many miles on the vehicle? Why did you change one coil?

Because of Code P0420 and I was advised by service center to change it. I had a problem of misfiring on Cylinder # 1 and mechanic has replaced the coil # 1. My vehicle is on 168K Miles now.

Carbon fouling is a bad sign - if the cylinders have carbon build-up, the shaking at engine stop may be dieseling - unwanted ignition from hot spots on the carbon. You may also want to get the compression checked. That can also cause misfires - I'm guessing your code is a a misfire code (PO30X) where "X" can be any number from 0-6.

Can you further describe about compression so that when I go to service center I can get it done correctly.

Are you 4WD? If so, the transfer case fluid also needs to be changed every 50K miles, which is a surprisingly short interval. Nothing to do with your problems today, but I always mention it in case new members haven't read the Owner's Manual yet.

I am not using 4WD. In fact the excels are removed and 4WD is disabled.

 

[Cooztwo]

What are excels?

 

[Cooztwo]

it took me a minute, you mean cv axles right?

 

[mqayyum]

Sorry for this typo error. You are right. It is axles

 

[stormsurge]

A code reader is cheaper to buy than a shop charges in most cases. Just fixed a car with the same problems, New timing belt/chain.

 

[Cooztwo]

If you take it to a service center there are two things in regards to compression, first is a compression test to get a value of how well the cylinder is sealing. The number should be somewhere around 200. With 168k miles, you may not get that high but close. Look for consistancy, all cylinders should be close in value. The scenerio goes like this: unplug the fuel pump relay, turn over the engine to verify it won't start and also clean out residual gas. Pull the coil packs, blow out the plug wells (get the dirt out), pull the plugs. install the compression tester in #1 cylinder, turn over the engine (i like to see 4 pulses of the needle before i stop), take the reading and write it down. Repeat this for all cylinder keeping track of the reading for each cylinder. Once that is done, if there are any cylinders that are low compared to rest, a tbls of oil is added to the cylinder and the test repeated, if the compression increases, then rings are likely worn.

The other thing to do is a leak down test. Logic says that if all cylinders are good then this test won't tell you much. But if a cylinder has low compression, this test adds compressed air to the cylinder to help locate any leaks. It goes like this: The tool installs like the compression tester except an air hose is attached. Put the cylinder to be tested at TDC. From here follow the directions for the model of tool. You'll need to calibrate it and install it. Once there is air flowing into the cylinder, pull the oil cap and listen, pull the throttle body and listen, exhaust is a little tricky, maybe pull the O2 sensor and listen.