MK1 JETTA 8V, Rough Idle , And jerky driving PLEASE HELP!!

[DUIIDAN]

Hello, everyone

Okay, so I'm at my wits end with this car..

Here's what its doing, its a Little hard to start if its been sitting for a few days, but when it does fire it idles perfect, and will continue to idle fine for about a 1-2 minutes, and then it will start to miss and the motor will shake as the idle comes down, and then it sounds like its got a big cam in it..
while driving the the car will accelerate just fine with no hesitation, and has good power, but if you just cruise the motor will shake and jerk, and you have to accelerate or coast get it to stop, and on deceleration I'm getting lots of pops out of the exhaust... and lastly I'm only getting 20-23mpg on the hwy..

its a completely stock motor, and has great compression, and I've replaced wires, cap and rotor, spark plugs, fuel filter, and checked for vacuum leaks using a can of starting fluid... NOTHING has made a single bit of difference, so I'm turning to you all before i take it to a shop and spend the money to have it fixed,

Anything info helps, and I'm sorry for the long post

[avw4me]

For the jerking it could be a worn out motor mount or trans mount. With the engine running give it a couple of revs and look for any play.

[JUS_GT_EYEZ]

I have never had much luck using the starting fluid method.. If you have not already, i would change your vaccum lines. It can be hard to find the leak in the original ones and at this point you are better off just swapping them out.

[DUIIDAN]

Well "avw4me" I thought the same thing as you as far as the motor mounts, but I jut replaced them and checked them all and they are still in great shape, it's a running issue that's making it jerk while driving..

And "JUS_GT_EYEZ" I've always had the staring fluid method work, but just in case I missed something, I made sure and checked EVERYTHING that could leak, and she tight as a drum, I'm starting to think that's it's a valve of some sort or cold start injector, or.... I'm just not very good ad diagnosing stuff...

I thank you both for your input, I'm going to work on the car some more today if it stops raining, ill go back thru and check for vacuum leaks.. and will check back to see if anyone else has and idea as well

Thanks again,

[VIP VR6 Rabbit]

Have you tried adjusting the timing yet?

Sounds like it runs good when cold because the cold start injector is working. When it gets warm enough the cold start injector stops and it starts to run rough. So I'm thinking you should pull the regular injectors and see if they're spraying good, if they're not it's because of a clog or fuel pressure issue. Here's some instructions from a different thread:

1) Remove all four injectors and place each into its own beer bottle.
2) Remove the large rubber intake boot from the airbox to expose the metering plate.
3) Locate and remove the fuel pump relay.
4) Jump the relay to run the fuel pump. The two slots to use are opposite each other and are orthogonal to each other (don't jump the two slots that are opposite each other but parallel to each other).
5) With the fuel pump running, slowly lift the metering plate with a magnet, clamp, pliers etc...
6) As you lift the plate, the injectors should start to "sing", then dribble, then spray. The spray should look like spray paint coming out of a nozzle, and the injectors should fill the bottles at about the same rate. They should shut off completely when you drop the plate.