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Sluggish 98 infiniti i30 tuneup

i am first owner of 98 infiniti i30. it has 147k miles on it but its been sluggish lately. when i got SES light on 2 years ago, I ended up replacing:

  1. spark plugs (all 6…NGK platinum)
  2. ignition coils (all 6. this was the one that caused SES light to go on)
  3. knock sensor
  4. drive belts

its not at all smooth when i give it gas. i can feel like sort of drag or whatever. am getting around 22 mpg on highway. it used to give 28 mpg before all this mess.

if there is good mechanic who knows these in detail i’d love to let him fix this. don’t want to get ripped off by dealer.

i live near san jose, ca. i think this car still has good life in it.


just to add, i always use 91 octane gas, tires are properly inflated, brakes are good.

Is this all of a sudden just happen??? Or doing it gradually over time??

If you’re feeling a drag…I’m wondering if it’s a caliper sticking???

How many miles since your last tuneup???

As for mechanic…There isn’t anything special with this car…Any decent independent mechanic should be able to diagnose the problem.

Have you ever had the transmission serviced? Have you checked the fluid level & condition? (I’m wondering whether the perceived “dragging” might not be a bit of transmission slip).

When is the last time it got a new air filter? Fuel filter? Perhaps now is a good time to have the fuel pressure checked.

Ever clean the MAF sensor? Throttle body?

Thanks for your replies. I cleaned MAF 2 years ago. Not throttle body.

Sorry if I’m not clear…what I meant by drag is some sort of resistance when i give gas.

It became like this since the SES light came on and I mucked around with replacing those coils, knock sensor etc. I got knock sensor from ebay. Not sure if its genuine but the SES codes I got showed issue with knock sensor and ignition coils. After replacing them both SES light went off. This was my last tuneup time at around 130K miles.

I replaced air filter few weeks ago.

I could try transmission fluid check, fuel pressure check.

The drag when you step on the gas pedal, especially if it feels like it is stuck a little at idle, is due to a dirty throttle body. But that is not the cause of the sluggishness or reduced fuel economy.

Is there an SES light on now? Have you checked for pending codes? A pending code is a condition that is not detected frequently enough to turn on the SES but will be stored in the ECM.

there is no SES light now. didn’t check for pending codes.

its kinda hard to explain all this to a mechanic. i took this to someone down the street (mechanic at gas station) and he said car is just fine. having driven this for 10+ years I know its no where close to what it was, say, 5 years ago.

Start with a check for pending codes. In California, they tell me that the car parts stores like autozone are not allowed to read codes for free, you can buy a cheap code reader for about $40 and read them yourself, probably for less than you can get them read at a garage.

Another thing to look at is the tach at 60 mph. I always take note of the rpm at 60 mph on all my vehicles. If it suddenly increases, then you may be looking at a transmission problem.

Since it is summer, are you using your AC? Have you driven without the AC on to see if the power is restored? Have you jacked up all four wheels and spun each wheel to see if you feel extra drag?

at 65-70mph, the RPM indicator stabilizes at 2500. during SES light on and before replacing coils it used to go to 2000 and do sudden drop. after replacing coils (all 6 maynot be from same manufacturer as I got some from kragen and some on ebay) it seems to go up gradually and stay at 2500 on highway.

even without AC i feel the power loss.

If there are no codes present I would connect a vacuum gauge and check for a partially clogged converter.

Partially clogged converters are not that rare with an aged, high miles vehicle and depending on the severity of the clog some people may not even notice it.

Another possibility could be slipping automatic transmission, slipping clutch if a manual transmission, or a timing belt error if that area has been delved into.

at 65-70mph, the RPM indicator stabilizes at 2500. during SES light on and before replacing coils it used to go to 2000 and do sudden drop

Find your best local transmission shop - one that specifically does transmissions and ask them to get it on a scanner & check out what is going on. What you described there suggests an inoperative torque converter clutch. This will affect gas mileage. This should set a code, but many manufacturers have transmission codes that won’t set a light or be picked up by a basic code reader - I don’t know about Infiniti. On that note, it wouldn’t hurt to check your throttle position sensor. That can be done easily in your own driveway with a basic voltmeter.

ok4450’s suggestion about checking for exhaust restrictions is also an excellent one.

i replaced a bad coil (one that i bought on ebay parts seller) and i could see its much smooth at idle. before i could sense some roughness at idle (say when i come to a stop at signal). am going to check for any improved mileage now. should know in a week or so.

i also notice a small knock at 10mph and 30mph. could that be due to transmission internally changing gears?

i hooked up OBD2 scanner that i got from autozone and it didn’t pull any codes.

thanks for your suggestions

also my drive belts are making large squeaking noises when i start the car. after 15 seconds or so those noises die. all 3 belts (from kragen) were changed 3 years ago. could that also be causing any issue?

i’d like to get some good belts and change if i could.

No change in mileage. It still at 22mpg. Showed it to nissan tech. he was also like there is nothing wrong with the car and such performance should be ok considering car is not new anymore. he said there is no transmission slip. at 60MPH RPM is around 2000.

should i replace 6 coils with one from nissan? current coils seem to be ok and there is no OBD code on car. replacing 6 with nissan coils is very expensive but again its not guaranteed that coils are the issue.

could catalytic converter be an issue? is that what when someone said check on clogged converter?


I would think it’s either a cat issue, dirty fuel injectors or a lazy O2 sensor. They can check the back pressure on you cat. You can have the fuel injectors cleaned. I add injector cleaner to my car at every oil change. You could try swapping out the O2 sensors one at a time with a new one to see if it corrects the problem.

The belts are either loose or glazed. It could be the auto-tensioner causing squealing. I would put on new belts and tensioner and go from there.

Have a helper rev the engine gently in park while you listen at the back of the car.
How does the exhaust sound?
How’s the air filter and PCV system?

In this order:
Try a bottle of Techron in a tank of gas.
Check fuel pressure.
Check compression, dry and wet.

I tried redline i believe few months ago. that was the first time i put a fuel system cleaner since i bought this car in 98. the nissan tech guy gave me some other cleaner and asked me try it. he got like a stack of them in his garage and he said they work well on nissans :slight_smile:

he checked quite a bit of details which gave readings like MAF percentage etc with some mac tools car scanner and said all readings look ok.

will request him to check on fuel pressure, compression and O2 sensors as well.

thanks again

One more thing. One of the mechanics I showed earlier said he could see black soot emitting out of exhaust pipe. does that mean converter or some component is bad?

Black soot means the engine is running rich. This could be caused by a leaking fuel pressure regulator, clogged converter, or even something like low compression; with the latter being far more serious of a problem.

Checking all of those things are easy to do and compression is something that should always be checked whenever an engine performance problem exists and the spark plugs are out. Unfortunately, that is seldom done.
Remaining optimistic, I’d venture to say the compression is fine at 147k miles.

Checking for a clogged converter is also easy to do. This can be done in minutes with a vacuum gauge and this is also another one of those unfortunates that exist. Many mechanics don’t own a vaccuum gauge (cheap and easy) or use them.