My 2000 GTP @ 140K miles is running horrible only while idling and shakes my whole car. As soon as I hit the gas the engine seems to accelerate perfectly smooth with no roughness at all.

Mechanic told me it's definitly misfiring. 3 different mechanics including 1 dealership have looked at it and can't figure out what the cause of the problem is without tearing the engine apart.

One person suggests a valve job, another suggests bad fuel pump or injectors, another suggests replacing the engine! gulp

Any thoughts? I love this car and would hate to get rid of it.

Start simple. What have you changed out, if anything to eliminate possibilities? Plugs, wires, coil packs, injectors are any one of the possibilities.

If those are all confirmed okay, might try a compression test. It's possible you've popped a piston.

If he popped a piston it'd run horrible all the time not just at idle... Not to mention all the other symptoms he'd be seeing...

Things I'd look at... Plugs, wires, injectors, coil packs, icm, and maf...

Real quickly, unplug the maf sensor when you're sitting in the driveway and see if the engine smoothes out any... If not the it'll probably be one of the other things.

step one: get new mechanics

Is it setting an SES code to show what is misfiring?

As was stated before, clean the MAF sensor. It is very simple to do, and it smoothed out my idling issues.

I pulled off my MAF sensor and I did notice an improvement in the violent shaking although it still shakes some.

I have replaced my spark plugs, wires, and momentarily swapped my coil packs out for brand new ones with no difference.

One of the mechanics that hooked his computer up to my engine told me that the codes were just telling him it was misfiring, but it was not being specific.

Another mechanic told me he did a compression test and the test came up with 2 cylinders at 150 and the rest were around 100-110.

I hope I am getting closer to narrowing this sucker down!

Again, get new mechanics!

that is good compression for and engine with that many miles, so you know its now rings or anything like that, take your car to AutoZone, have them read the codes, your first mechanic should have the information on what cylinder is misfiring... He was probably trying to get you to leave the car there and charge you and arm and leg... Once you have the SES codes, post them here and that will give us a better idea on where to start.

100-110 is not good compression and with a 50lb variance you have some magor issues,you need to do another compression check and then a leak down test.Chico.

sorry I read that wrong, might wanna get a compression tester to double check it yourself and find out what cylinders are lower... I know the AutoZone here will "rent" them out, basically pay for the value of it and get a refund when you return it

Well rings are not usually an issue with these motors till very high mileage but the cyl.heads do have some problems (cracks between the valve seats)which may be your problem.Chico.

Would messed up cylindar heads make it run rough during idle and run smooth when accelerating? My car seems to run smooth and fast when I punch the gas. It's just when I have come to a stop that the car shakes like crazy.

Oh boy thats a tuff one there are just too many hings that could cause a ruff idle,a faulty injector,weak spark at idle (coil or wires) ,a vacuum leak,a worn cam lobe and the list goes on you need to find a competent mechanic to narrow your problem down and eliminate possible causes ,sorry I could'nt help more but this is a hands on issue.Chico.

x2....chico knows all

im having pretty much the same problem with mine, and i went through a whole lot of attempted fixes before narrowing it down to bad valves. i hope for your sake that you can fix it with something little.

Now that you mentioned faulty injector; a few days ago I put Cheveron Techron into my empty gas tank and filled it up. I just noticed yesterday that the shaking in the engine has lessend. I wonder if this could be some sort of fuel supply problem. Couldn't faulty injector or a faulty fuel pump cause a misfiring?

Thanks for all of your help, guys.