I stored my vehicle for 4 months, unhooked the battery, returned, fired right up and no issues except a very rough idle.

My boyfriend has been working in my car for years and he read about some possible causes for the idle issue.

On a cold start, it’s fine for several minutes, but then it begins to idle roughly and the whole car bounces. If idling a few minutes, it will smooth out, but then go back to bouncing. On idle, if I give it a little gas, it smoothes out or if I put it in Park or Neutral, it’s not as bad, but back in Drive, it’s rough. Running on Premium. No issues once moving.

No leaks between in air filter and the engine. Less than 5 K miles ago, we replaced the air filter and mass air flow sensor and replaced the following within the last two weeks:

New fuel injectors, all 8
New spark plugs, all 8
New coils, all 8

Not one of those made a difference.

Is there something we are overlooking? What can we try before taking it in for an expensive repair?

Thank you in advance.

 

Codes? Need STFT & LTFT numbers from a data list. If you have the old MAF sensor, (hopefully the oem Denso) clean it way up inside that little pipe and reinstall it. If the MAF sensor you have in the car now is aftermarket, I’ve had quite a few of those go bad. I’m not saying that’s your issue, just my experience with A/M MAF’s. Other possible issues could be intake manifold gaskets leaking air, brake vacuum booster junction below the throttle body on the passenger side.

 

Almost always bad timing: have you updated your secondary tensioners?

 

Thank you. We will check this out.

 

Is the gas the old stuff that you put in 4 monthsd ago? Might be as simple as bad gas. Timing tensioners should be checked, 100% but I would imaginu if timing were a problem it'd never run smoothly at all.

 

Thank you kindly for your reply. Both tensioners have been replaced. One about 12k ago, but yes, could be the issue.

I’ve filled it with premium after running it down to empty and added Lucas to it 2 times in the last month. I don’t think the gas.

My mystery car.

 

Tried a priest?

 

As suggested, you should read the fault codes. When it starts idling roughly, what rpm does the tachometer show?

 

Think about it for a minute. You parked your car, removing power from all the systems.
The gremlins didn't get in there and change the timing nor did the bad elves poison your
sealed gas tank. What did happen however, is difficult to diagnose because of the sudden
nature of the problem. Electrical issues may manifest themselves due to the corrosive
nature of unpowered systems, such as at the various grounds so checking those points
of connection might be a good place to start. Another place of concern is the many and
various vacuum points which could fault the required flow of fuel. Rubber and plastic do
not age well and cracks and therefore leaks seem to get worse when not used for a while.
A good code reader should aid you in determining places where to look for the trouble.

In the future place a battery tender on the car and do not remove power from the system.

 

Took it in for a code reader and replaced top of the possible issues it said it might have.

Replaced mass air flow sensor with new #1 on list
Replaced O2 sensors both upstream and downstream # 2 on list
Replaced fuel injectors, all
Replaced coils, all
All new spark plugs

Car idles smoother, but once it warms up, it’s still a bit rough at stops, more so in reverse.

…. any thoughts on why when it warms up, it still idles rough?

Could it have anything to do with exhaust? We can’t think of anything else we can do ourselves.

 

There is a high probability you have a vacuum leak. That is the number 1 cause of a rough idle. You can
use a scan tool with live data to read the short and long term fuel trims. If the computer is adding fuel to
compensate for a vacuum leak or unmetered air, your fuel trim readings will be high, usually above 10%
(the range is -25 to +25). If fuel trims are high, suspect an air leak.

 

Does it idle rough in neutral and park as well or only when in gear...like when you get where you're going, car is all warmed up, was running rough at the stop sign, when you put it in park does it still run rough? Wondering if its not even a motor issue.

Sometimes I like to look at what a problem is NOT instead of what it IS. Work KT training wasn't 100% forgotten!

 

Trimms goes up too when fuel pressure is low. Only code read is not useful. You have to look livedata from the ecu as RandyS said. Describing only rough idle is not enough information. Front lambda sensors heat up very fast so you can see what the short and long term trims are doing when the engine is cold. And where to they move along the engine heat.

 

As I stated in my first post, need short and long fuel trim results. I know it’s a challenge for some to fulfill that requirement. It tells a lot of the story but not all. Without having the STFT & LTFT information, this next part is something to look into.

As far as the rougher running in reverse, that to me sounds like collapsed engine and transmission mounts. The mounts are liquid filled (excluding transmission) and when the rubber around it collapses and/or tears open, the liquid leaks out causing more vibration. The supporting nature of the mount is really no longer there and neither is the vibration dampening.

 

Good point about the mounts. I had no idea they were "cream filled"!

 

I am having similar (exactly the same!) problems, and have already replaced the oxygen sensor which came up as an issue on the diagnostic thing. The mechanic is pretty sure it's the tensors, and if not the timing belt, so I'd hazard a guess that it is a similar problem for you. I haven't done the work myself as it is a bit pricey, so the car will have to wait a couple of months sadly, so I can't tell you if that solved my problem.

I didn't know about the engine and transmission mounts that Addicted2Boost points out, and so will look at that as an issue with mine also!