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Rough Idle

I have a 2000 Infinity Q45 with 99000k. When stopped at a light it sometimes idles like it wants to stall. This did not start happening until after the dealer did the 60000k major service. I have had them check this numerous times and they say the computer does not give them an error message. They have checked the fuel injectors and say they all appear to be working properly. I have tried fuel injector cleaner and fuel line cleaner. When it has the fuel line cleaner in the tank it doesn’t do it. Their latest suggestion is to replace all eight fuel injectors for a hefty sum of money and it “may” fix the problem. Do anyone have any other suggestions?



Mike in DC

I suggest that you expand what you worry about past fuel - to spark and air.

Rough idles are often caused by vacuum leaks. Check for those. This could be as simple as a vacuum hose that was damaged or not replaced during the 60K service. A vacuum gauge would give you a clue w/in about 10 seconds. Rough idle can also come from a sticky idle air control valve. That is easy to clean. I would also check the air filter, and while doing it would clean the MAF sensor.

Did a 60K service include new plugs and wires? Has anything been done to check the ignition system?

The dealer has done numerous computer checks and does not find a problem. The service tech has even sat in the car while it is doing it. These days unless a computer tells them what is wrong they don’t have a clue.

The dealer may not be able to find a problem without a code (although I suspect he just isn’t interested…he’d rather sell you a replacement vehicle), but any good independently owned and run shop should be able to. There are a number of possible causes, my first wild guess would be the IAC motor, my second an EGR valve or vacuum solenoid, and a good shop will be able to diagnose it.

So this has been happening for 39k miles? And the dealer cannot find the issue? Try and indepenent shop. Even a Bear analysis system connected would show the real time spark and fuel pressure status. These do not use codes the measure what the engine is doing. Sorry but the folks you were working with just are not up to stuff. The injectors can be individually checked using tools the synchronize the power output to the firing cylinder. Its a fancy test but replaceing one or two failed injectors might be easier if they are not buried in the engine. Otherwise pull them all put in new but get a different shop to diagonse and do the job. Too bad you did not fail emissions because that would but the dealer on the hook for the whole price. It is unacceptable that the dealer would not fix this for this amount of time.

Don’t deal with any shop be they Dealer or Independant that says they must have a code to fix a car. This advice is for all our readers not just masimj.