I have a '98 Q45 with 90k miles and have had it since 62k miles.

I'd like to ask about O2 sensors, MAF's and other sensors.

Do they degrade over time? Is it worth replacing any sensors/monitoring components even if you have no codes or does the old adage "if it ain't broke, don't fix it apply?

Can the wires on the MAF be cleaned?

Recently my car seems sluggish, especially at lower rpms in 2nd gear. I get a hesitation or a bogging down (like a carberated car in the cold weather with the choke on and that might need a tune-up), then as the rpm pick up over 2k, it seems to pick up steam. Idle is very smooth and startup is fine. A few times it almost seemed as if the transmission was slipping. It's a rebuilt from Infiniti, installed at 67k miles.

No noticeable missing at higher rpm. I did the plugs 20k miles ago, they should be fine. Cleaned the K+N air filter 2k miles ago. I have to check my records to see if I ever did the fuel filter.

I'm going to put Techron in, put a clean paper air filter in just 'cause I have one handy.

Any suggestions are much appreciated!Don Cummings

i have noticed the same problem on my 95Q and i already replaced my o2 sensors

Did you notice any improvements from replacing the O2 sensors? Better mileage?

Do the o2 sensors if they're original. The MAF can be cleaned, but only with extreme care. Use a q-tip soaked in alcohol.

i noticed no difference the improver gas milege is when my wife drives

I am concerned about the K&N oil and the filter in general is it a cone or drop in?

The drop in while doing no good [1/4% at most] can coat the MAF element with oil film making it sluggish in response and incorrect in relaying correct air flow to ecu.

Have the engine Consult tested for failed knock sensors [very common by 100k [on 90-01Q].

Throttle body and plenum, runner induction clean.

The power ouput below 2,000 rpm is marginal especially with AC on.........every part must be clean as new to avoid the lugging sensation.........which gets worse as the temps rise.Techron is decent but won't really clean dirty injectors as much as you think, better than nothing if you use it with Chevron gas at every tank fill up.

The K+N is a drop in. I agree about the oil and tried to be very careful not to over oil when I last cleaned it.

I will clean the MAF tonight with a q-tip as suggested and post results back tomorrow.

How much effort is required to replace the knock sensors on a '98Q? Seems like from what I've read they don't last forever and I plan to keep the car for several more years.

NEVER NEVER TOUCH THE MAF ELEMENT with anything solid!!!!!!!!!Spray brake cleaner [light pulses thru the protective screen] a foot away is as agressive as you want to get...........new ones are $450.

97 knock sensors and harness are easier than on 90-96. Seem to remember 4-5 hours after you have done 20-30 sets.$800-$1000 job anyway you look at it.

Don't bother changing then till they show a code on Consult, as your local heat driving conditions could mean they are fine.

If you plan on keeping the car a long time [above 200,000 miles]burn that K&N filter and use oem and change them every year! Hopefully you haven't allowed too much top ring wear so far.

4-5 hours to do knock sensors.....so I assume the whole plenum has to come off.

I've heard mixed things about K+N. Have you seen first hand wear issues when using K+N vs. stock paper elements?

duck3986 wrote:Any suggestions are much appreciated!Don Cummings

Don, fill in your profile so anyone can know at a galnce where you are and what car you have and any information about it you add to your profile.

The K&N just plain don't filter as well. That is how they can claim their "performance" gains. Why risk downstream damage when OEM works so well and is so inexpensive from Joe?

I am ashamed to admit I ran a cone filter for 70,000 miles [about 3 years] from 45,000-115,000 miles. Before I became smart and started testing things.

A return to oem air box and exhaust solved so many funky things I couldn't resolve, till then.

See I trusted the hype too. Slick ads and all

I blame my low at idle compression [gets better at 1500 rpms when the engine warms up and meets running compression calculations*...........Every Q engine we've tested has higher cranking compression than mine [even those in the 250k range]......except those that blow blue smoke.........all the compression leakage is from rings.

Since I've changed my oil 66 times in 264k we won't blame that and obviously with good above spec oil pressure the bearings are not worn...........so it had to be from the induction system [dirty air].

If I had been doing oil analysis I probably would have seen it from high silicon and particulates in the oil.

* running vacuum [2000 rpm = 18" or 40% of atmosphere 5.7 psi x 10.2 = 58 psi** for each cylinder no spark plug cut off injector and just cruise at 60 mph [2000rpm] running on 7...........you check the highest and low cranking conmpression cylinders this way.** with injector cut off the air flow is not displaced by the fuel volume so 5-6% variation is normal Actually checked all 8 took all day [55-61 psi].At these low air flows [cruise] nothing past [or before] the throttle plate is any kind of restriction.

Last night I pulled my MAF and sprayed it well with brake cleaner and put a paper air filter in.

This morning the car ran fine. It hadn't been running awful, but there was a noticeable sluggishness below 2200 rpms, especially in 2nd to 3rd gear. Now it seems to pull stronger and smoother.

Thanks for the suggestions!