[FlyForce]

I recently acquired a mustang that has been sitting in storage (aka. a back yard) for the past 3 or 4 years. It's a 1998 Mustang 3.8L V6.

I got it and it looks to be in good condition. Just a side collision has the driver door and fender replacing.

I only had to replace a fuel pump to get it up and running, yet it still sounds a bit rough. I'm hoping it will clear up quite a bit with some running and tweaking, but I'm still in the progress of figuring that out. However, it sounds very good in the higher RPMs.

However, there is a problem when the car idles. From 1,300 RPMs to below and idling, the whole car shakes noticeably. If I put the AC on, it is far worse, with the whole car shaking fairly aggressively. After I let it run awhile, the shaking is less harsh, but with the AC on, it is still pretty harsh.

I am not that mechanically inclined, however, I have been wanting to learn (thus my changing the fuel pump myself and such). So I am hoping someone here can throw out some ideas or let me know what I should look for, so I can diagnose what is causing this.

Any help is greatly appreciated!

[mustang227]

Try replacing the spark plugs

[FlyForce]

Originally Posted by mustang227 Try replacing the spark plugs

That was the first thing I did when I got the Mustang. I actually had to because the spark plugs looked horrible.

[clidefr0g]

When gas sits it deteriorates into its base material, crude oil. Gas is only good for about 1 year tops, any gas left in the tank over those 3-4 years is probably so bad its like burning mixed gas for 2 strokes or worse. Not to mention the tank but also anything left in the fuel lines/filter/injectors, everything probably needs cleaning.

[davidstivers09]

Its definitley bad gas, I would get that gas out, and change the filter

[FlyForce]

New gas and cleaned out the tank when I changed the fuel pump (as noted above). So it definitely isn't that either.

I also have changed the fuel filter, oil filter, and gave it an oil change, along with changing the fuel pump.

[davidstivers09]

Damn, maybe the fuel lines are stopped up?

[southfour!]

Try seafoaming it, then change the oil again

[davidstivers09]

My uncles mercedes acted like that, and still does if he doesn't drive it for a while. Maybe you just have to keep driving and driving, until all the bad gas is out?

[southfour!]

Originally Posted by davidstivers09 My uncles mercedes acted like that, and still does if he doesn't drive it for a while. Maybe you just have to keep driving and driving, until all the bad gas is out?

Why would you drive with bad gas when you could simply drain it, and the op already has changed the gas when he changed the pump.

[davidstivers09]

I'm not exactly sure, it probably has to do with the fuel lines, we're still trying to figure out exactly what is wrong with his benz.

If it sets for a week, the gas seems to be bad, then it has problems starting and when it does finally start it ends up dying? Lol. So we take the gas out, and then put new gas in it, and it starts right up and as long as you drive it daily it'll never have a problem but as soon as it gets put back in the garage it does the same stuff over and over, its like it has a mind of its own!

[southfour!]

Originally Posted by davidstivers09 I'm not exactly sure, it probably has to do with the fuel lines, we're still trying to figure out exactly what is wrong with his benz. If it sets for a week, the gas seems to be bad, then it has problems starting and when it does finally start it ends up dying? Lol. So we take the gas out, and then put new gas in it, and it starts right up and as long as you drive it daily it'll never have a problem but as soon as it gets put back in the garage it does the same stuff over and over, its like it has a mind of its own!

i was refering to this part lol

Originally Posted by davidstivers09 My uncles mercedes acted like that, and still does if he doesn't drive it for a while. Maybe you just have to keep driving and driving, until all the bad gas is out?

[davidstivers09]

Oh, lol, I'm just saying like to flush the whole fuel system out. Sorry if I'm hard to understand

[Thonner]

I would certainly start with Seafoaming it. Sounds like idler senser might be gunked up.

[k_brute]

Are the rpm's dropping when you have the vibration or is it holding steady? Does the vibration seem to come from the engine, the driveline under the car, or the exhaust?

Could be lots of things....with your issues (especially the A/C issues) try:

1) Vacuum lines...are there any leaks/hoses that have deteriorated after a long time outside?
2) Check your IAC valve. These things go bad all the time. The engine might not be getting enough air at idle through the valve. Take it off and check for excessive build up and/or replace it. It's not a cheap part but its a 5 minute replacement and easy to do.
3) A/C charge may be low causing excessive drag on the engine when its on. Is the charge in the system OK? The A/C also relies on the IAC valve so extra points go to #2.
4) Excessive vibration could be caused by a broken engine mount. This is unlikely unless the previous owner drove it hard, but I would check just to make sure.

Just a few suggestions to get started.

[gloomshadow]

Originally Posted by k_brute Are the rpm's dropping when you have the vibration or is it holding steady? Does the vibration seem to come from the engine, the driveline under the car, or the exhaust? Could be lots of things....with your issues (especially the A/C issues) try: 1) Vacuum lines...are there any leaks/hoses that have deteriorated after a long time outside? 2) Check your IAC valve. These things go bad all the time. The engine might not be getting enough air at idle through the valve. Take it off and check for excessive build up and/or replace it. It's not a cheap part but its a 5 minute replacement and easy to do. 3) A/C charge may be low causing excessive drag on the engine when its on. Is the charge in the system OK? The A/C also relies on the IAC valve so extra points go to #2. 4) Excessive vibration could be caused by a broken engine mount. This is unlikely unless the previous owner drove it hard, but I would check just to make sure. Just a few suggestions to get started.

Yeah, all good stuff...could also be the cam position sensor or possibly a stuck injector..Ive had them both happen and the result is a rough idle and the motor will run like shit.

[Mr. Red Pony]

could be oil/sludge built up on the rotating assy. from sitting so long. Change the oil, fuel filter, and plugs. Clean the IAC, EGR, MAF, and 02s. Also Seafoam it.

This would make any car run smoother. So it should do a wonder for one that has been sitting for years...

[FlyForce]

Thanks for the great suggestions everyone. I am going to be trying out all of those things as soon as I can.

Also, how does this seafoam stuff work? I am still trying to figure out all this stuff. I did pick up a repair manual, and that is how I managed to fix my fuel pump. But I am still very much learning the basics about cars.

Thanks again!

[Mr. Red Pony]

It cleans out all the carbon that builds up in the engine. Improves throttle responce and gas mileage somewhat.