Light misfire while at idle

[LIBRILZ]

Just got a 98 Q45 and man I'm excited, it's not even mine buut still. lol. Anyways the car has a slight misfire/blip when at idle. Otherwise like on the highway it's smooth sailing.

The previous owner just changed all the fluids and belts at 90k, I think they might have changed the plugs to and maybe not used NGK plugs. It that's the case I would guess this could be a cause, also a bad coilpack or coilpack wire possibly?

I searched about this item and that's what I've come up with, there aren't any injector issues on these model Qs right? Like I said, the mis is really light but it's noticeable and you can hear it, only at idle, and the car hauls a** just fine.

[Q451990]

Usually the coil failures come with a missfire code and a "check engine" light. Does your "check engine" light come on? Does it come on with the bulb self test when you turn the key to the on position? You wouldn't be the first guy to buy a used car with a missing "check engine" light bulb!

As you said, the injector issues that plague the first generation Q don't seem to be an issue with your series of Q, but it's always possible. Especially if it's clogged...

Welcome to NICO!

Heath

[elwesso]

Honestly what I would try is the old fashioned "italian tuneup". Take the car out on the interstate/back road and redline it a few times... There might be enough gunk buildup to cause that..

I always notice after my Q is run really hard it seems to idle a lot better!

[Q45tech]

Idling has always been tough since even with heated O2 sensor the O2 may not provide accurate A/F readings so the ECU reverts to pre/prior factory values. It knows rpm and old injector timing but that may be incorrect UNLESS injectors are PERFECT as they were brand new!

Same applies to 1996 fuel quality [when 1998 was programmed].

Dirty air path is the first place to look and get everything clean as brand new all the way to piston crowns!

[Infinitiguy19]

So your saying that fuel injectors, pump, control unit and cleanliness of intake is the only thing the matters at idle?

There are absolutely nothing else that matters?

[rxm6]

So your saying that fuel injectors, pump, control unit and cleanliness of intake is the only thing the matters at idle?

There are absolutely nothing else that matters?

No, I don't think he is saying that. I think q45tech is saying the intake and fuel injectors and their cleanliness is a good place to start to remove your light misfire.

[Q45tech]

There are methods to view the spark voltage and measure the pressure inside cylinder in real time so you can allocate the fault among the dozens of things that could cause misfires at idle.

Most people don't has access to engine labs and technology so they just change spark plugs and clean things. As is recommeded in FSM to start dealing with misfire.

Few would have access to labs with BTU Bombs Calorimeter to measure the gasoline heat production capacity. Anyway the gasoline is nearly the same in each cylinder [assuming clean injectors].

The ecu does all it can to maintain idle rpm by changing injector squirt volume, ignition advance [bank to bank], air flow [IAC].A single misfire happens to fast that the flyweel doesn't allow AVERAGE rpms to drop very much.

A very sensitive person can feel a partial misfire [lower pressure] sometimes better than older ECU.

Condition of engine mounts [rubber] defines the feeling.

[Skibane]

Honestly what I would try is the old fashioned "italian tuneup". Take the car out on the interstate/back road and redline it a few times... There might be enough gunk buildup to cause that..

I always notice after my Q is run really hard it seems to idle a lot better

+1.

Since the car is new to you, it probably wouldn't hurt to run a can of fuel system cleaner (BG-44K or Redline) through it at the same time.

Fuel cleaner + high RPMs = most effective deposit removal.

Be sure to change your oil soon afterward: Some of the deposits removed by the cleaner end up in your oil pan.