slight vibration at idle

Check for engine misfire trouble codes and when and if you get a P001-006, check for an intake manifold vacuum leak near the cylinder that is misfiring at idle.

Engine still runs when MAP sensor disconnect. i am having trouble with idle, seems to be missing when cold. it gets better when it warms up but it is still there. no codes set. bad gas mileage, slight vibration in steering wheel, and body.
Thank you for the help again.

slight vibration in steering wheel at idle. no codes set, runs good, other than bad gas mileage about eleven mpg.

That is terrible mileage for the 4.0. I would start with an injector balance test after a through visual inspection of the injectors. They are a known weak area on that engine. They will heat up and the housings crack. This may not set a check engine code if it is not bad enough to cause a misfire.
To do the injector test you need an injector activation tool and a fuel pressure gauge.
You attach those tools then turn on the key to cycle the fuel pump. Record the pressure and then activate the injector. Record how far the pressure drops. Repeat the process for all six injectors. Then you compare the results. The drop should be close to the same for each injector. If you find any that drop more then they are faulty.


https://www.2carpros.com/articles/how-to-test-a-fuel-injector

still gets about eleven mpg. i have everything i can think of. help please. thank you for your time.

What have you actually done to the vehicle? Have you scanned the vehicle for any trouble codes? If you have codes, can you post them on here please. If you can get a scan tool to read the codes here is a link to help you pull the codes:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

i cannot get over twelve mpg. it runs great, does not seem to have any problems. thanks for your help.

Stop on a slight incline, shift to neutral, release the brakes, then see if the vehicle creeps downhill on its own. If it does not, one of the brakes is dragging. You should be able to identify which one after a drive at highway speed by feeling for the one that is real hot.

Look for excessive black soot inside the tail pipe. If you see that, the engine is running much too rich. You will need a scanner to look at the sensor readings the engine computer is seeing to determine why it is requesting too much fuel.

rpm shows 650, will run eight mph at idle, and vibrates at stop light. can feel in steering wheel and brakes. when i raise the rpm just a hair it goes away, other than that it runs perfect. it has not set any codes. thanks for your help.

I would consider the idle air control motor, this is controlled by the PCM with inputs from other sensors a scanner with live data can watch the inputs and see if the IAC is responding.

the gas mileage on my vehicle is getting worse. i am not getting more than nine to ten miles per gallon. Please help! thank you

First read the diagnostic fault codes to rule out any obvious problems. You can do that yourself by cycling the ignition switch from "off" to "run" three times within five seconds. Leave it in "run", then watch the code numbers appear in the odometer display.

It takes a specific set of conditions for a fault code to set to indicate a sensor circuit is causing a problem. Before that occurs, it is also possible for a sensor to develop the wrong signal voltage but one that is still within the acceptable range. If it stays in that acceptable range, no fault code will be set to direct you to the circuit that needs to be diagnosed. For that, you have to use a scanner to view live data and determine if any reading looks suspicious.

Besides sensor readings, the scanner also shows fuel trim numbers. If you see high positive numbers, it means the engine computer is adding fuel to the pre-programmed starting point. It thinks more fuel is needed in response to something, and we have to figure out what that is. If the numbers are high negative, it means the computer wants less fuel than normal, and we have to figure out why too much fuel is going into the engine.

Those are problems for an engine performance specialist. The clue is there is usually some related fault code set to get him started. When there are no codes and no running problems, the next suspect is a sticking brake. The first observation is one wheel will be unusually hot after a short drive. Another potential clue is the brake pedal is higher and harder than normal when pressed. If you stop on a slight incline, shift to "neutral", and release the brakes, the vehicle should creep downhill on its own. If it does not, we need to determine if brake fluid is being trapped and is unable to release from one brake, or if a mechanical problem with that brake is the cause.