Weird vibration from my car

[SoCalV8]

Hey guys,

I'm new here, have had my Q45 for about 5 years now and just recently I have had a very strange vibration from the car when it is at a stop or at low idle. Sometimes it just vibrates, other time it jolts the car back when accelerating. I get horrible gas mileage as well , I use a half tank every 20 miles or so. Anyone had a similar problem with their Q? What can it be?

Thanks guys,
SoCalV8

[OwnerCS]

Welcome to NICO.

Is the vibration like an engine misfire -- like the feeling the car is running on 6 cylinders instead of 8?

Is a Check Engine Light on?

How many miles does the car have?

How long have you owned the car?

I take it you are located in So Cal.

[SoCalV8]

No doesn't feel like an engine misfire, but it does take a few seconds for the car to actually go from the time I accelerate. Like if I floor it I can count to 2 or 3 and the car will remain at the same speed and then take off.

Yes the check engine light is on, but for cats

180k

Me personally, 5 years, but it has been in the family since 2000

Correct, I am in SoCal

[OwnerCS]

Have the check engine codes been read since performance problem started? The car's system can store up multiple codes. Honestly, it sounds like there may be multiple issues behind the symptoms.

It is good you have access to the car's history for a long run. If I had just purchased the car with 180k and I didn't know anything about it, I would start with the following items:

1) Take it to AdvanceAuto or AutoZone and get a fresh check engine code diagnostic. If the check engine light is on, they will usually do it for free.

2) Without knowing any maintenance history, I would start with a Mass Air Flow (MAF) sensor check and cleaning. I would search this forum on MAF, as there a recent story about a Y33 Q45 and a failing MAF as I recall.

3) Did the cats burn out or have they been removed? If the cats burned out, failing/weak O2 sensors could be the cause. I've seen cats burn out on V6 powered cars due to O2 sensors that started failing around 130,000 miles -- but kept driving.

[SoCalV8]

Will go and check it out with AutoZone and I'm searching the MAF issue now. Cats were removed.

[JoeGarcia91]

Don't want to derail the thread, I just have a question, is 40-45 miles per 20 liters of gasoline (1/4 tank approx, the tank fills up with more or less 80 liters ) a good mileage on a 1998 Q45 Base?

[Q451990]

Nope... that's pretty bad, if your readings are accurate. That equates to about 7.7MPG, which is amazingly low. You should see twice that with spirited in town driving, and nearly 3 times that with gentle highway cruising.

Heath

[JoeGarcia91]

Oh, I am really sorry, I meant 40-45 miles per 10 liters of gas, I get anywhere around 80-90 miles with 20 liters (a quarter tank) The most I've gotten was about 102.3 miles on 20 liters, but that was doing crazy hypermiling crap until I ran out of gas just to check if HM worked.

[Q451990]

Probably about right then. I would expect somewhere around 15-17 MPG for in town driving, and 20 - 21... maybe 22 if you're really trying to conserve on the highway.