OK - the saga continues:

BACKGROUND: 8 weeks ago my 98, 3.4 v6 4x4 started to run rough when warm and at an idle. Plus, my gas mileage has gone WAY down & at one point the check engine light even came on.

REPAIRS TO DATE: So, in an effort to remedy this I have run the codes and done/replaced the following: tune-up (plugs & wires), intake manifold gasket, 02 sensor, coolant thermostat, cleaned MAF, done complete intake leak & vacuum leak test (no leaks).

RESULT OF ABOVE: Though the check engine light has not come on again, I still have the rough idle and lousy gas mileage.

SO in a last ditch effort, I (gasp) took it to the dealership and paid them for diagnostics and this is what they came back with "test-drove vehicle w/a scan tool, all sensor values were within spec, leak tested each CYL & found CYL #1,2,3,5,6 at 10%, found #4CYL at 25%."

QUESTION: What does that mean to you - the dealership says it means a $3000.00 valve job! Any thoughts.

My next step is to clean the IAC.

 

that means your getting 10% loss in all your cylinders except #4, it has a 25% loss... It may just need the valves adjusted, hard to say.

 

usually anything over 20 and a delership will want to pull the head. when you say rough do you mean a little vibration or was it misfiring?

 

No, no misfiring - just a rough idle. Rough enough that coffee in a cup in the dash cupholder sloshes around and the kids in the back seat says it feels like an earthquake.

 

Not sure what kind of vacuum leak test was performed but a vacuum gauge will usually fluctuate when you have leaky valve(s). The 25% down cylinder is a problem and should be addressed whether it be leaky valves or bad rings.

At $3k for a valve job, I would be tempted to shop for a junkyard motor. Tearing into your motor and doing just the valves might be a bit of a waste depending on the condition of your rings and bearings.

 

Try some seafoam, and let it sit over night. Try a cheap remedy first. There just may be build up on the valves. And im sure it wouldnt hurt to try

 

It is a leakdown test (positive pressure not vacuum).

I agree that 25% might be worth looking into on #4 but I have a tough time saying that your extremely rough idle is all because of that. I am very curious what CEL came on briefly but I guess unless it comes back, who knows. Have you also done a resistance test on the injectors? If not you might want to try that as well. Make sure you spray the MAF with brake cleaner because I found that the electrical contact cleaner wasn't getting the job done.

 

Brake cleaner & seafoam - OK< I am on it - worth a shot.

CEL has not come on again since I replaced the intake manifold gasket.

 

i would also try doing a wet compression test. that will indicate whether its your valves or your rings. a wet compression test is just pouring a small amount of oil in the cylinder after testing, then retest, if your compression goes up, its rings, if it stays the same its valves. i mean a small amount, no more then a capfull of oil.

oh and check your motor mounts, shaking that bad without a misfire sounds like a busted mount