New Maf - Rpm

[james250]

So i replaced my MAF sensor because of random sluggish power issues on my IS250 auto, cleaning the sensor didnt help much. I had very poor mpg too. I replaced the MAF and also gave the throttle body a clean. Since then mpg has improved and is pretty much like it used to be. I then changed brake pads and discs. And now on some random occasions while i'm driving the car just randomly does something and the throttle response becomes very sluggish as if i'm gone into snow mode. I stop at the traffic light, turn off the car and immediately start it within a few seconds and the car is back to normal. ( if i dont restart the car, then it just stays in that sluggish mode )

I've hooked up a OBD data logging app with the hardware to monitor the LAMDA sensors but they dont seem to be showing as rich or lean. I was suspecting it might be one of the o2 sensors, but now not sure. Is there any way I can diagnose if a o2 sensor is faulty? I have no check engine light either so that's not helping.

Any suggestions would really be great.

Thanks

[ColinBarber]

doesn't sound like an O2 sensor issue.

There would be a error code stored if the ECU detected an abnormal reading from the O2 sensor and you would get the CEL lit up. If the O2 sensor was just giving false errors without the ECU detecting it then you would normally still get normal performance under acceleration from standstill because it wouldn't be in closed-loop mode and therefore wouldn't use the O2 readings to fuel the engine.

What was the timeframe between replacing the MAF and brakes?

Worth checking you haven't damaged an ABS sensor on the wheel hubs.

[james250]

Thanks for your reply ColinBarber, changed the brake discs and pads about a day after the MAF sensor change. Other than changing the MAF, cleaning the throttle body and changing brake discs and pads. I didn't really do anything else. I did after a few weeks start feeling judder/vibrations on my brakes which I will check out this weekend. I was suspecting maybe sliding pins. Didn't know something brake related might be causing this other issue. Any way to check if its brake related?

Thanks

[tameracingdriver]

If you can get access to a laser thermometer you could see if there is any difference in temperature of the brakes at each corner. If one were hotter, then you may need to free up the caliper. When you worked on the brakes, did all the caliper pistons push back in easily? Did you clean and grease the slide pins?

What did you clean the TB with? Not sure which engine you have but is there an Idle Control Valve or Throttle Position Sensor?

I had an Audi A4 that had similar issues and it turned out to be the throttle pedal assembly (throttle position sensor)

[james250]

When you worked on the brakes, did all the caliper pistons push back in easily? Did you clean and grease the slide pins?

What did you clean the TB with? Not sure which engine you have but is there an Idle Control Valve or Throttle Position Sensor?

Thanks for your reply, yes the pistons pushed back easily with a G clamp. I didnt re-grease the slide pins as it looked like it had grease on it already, but i'm going to dismantle it this weekend and greese up all the pins and the bushings.

I used Wynn's Fuel Injection & Carburettor Cleaner to clean the throttle body, just sprayed it on and wiped off with a microfibre cloth, then with my hand pushed the plate to clean the rear side of the plate.

[james250]

A few other things I have noticed since changing the MAF sensor and cleaning throttle body is that when i start my car first thing after it's been sitting, in the past my idle used to be about 1600rpm and it would be steady on 1600rpm and will slowly go down, but if i put it on Drive, the rpm would drop which was normal. but now when i start my car idle starts at about 1600rpm then within a few seconds starts to go down all the way to 1000rpm and then surges back to 1600rpm and back down. Never had this unsteady rpm before.

Also, during the first startup i noticed that if i get out of the car while it is idling and go to the back of my car the fumes smell a bit like fuel, dont remember it being likely this before.

any ideas guys? i'm wondering if while cleaning my throttle body i might have damaged it somehow? the MAF sensor is new. when cleaning the throttle body i moved the plate about by pushing it to clean it

[ColinBarber]

It might be worth cleaning the MAF sensor. You may have used too much TB cleaner which has coated the wires.

Not for the same engine but may help:

http://www.lexusownersclub.co.uk/forum/tutorials/article/104-gs430-43-3uz-fe-engine-cleaning-maf-sensor/

Also make sure you haven't dislodged a vacuum pipe and introduced an air leak into the intake system.

have you tried using the old MAF sensor again?

[james250]

I havent tried the old MAF sensor, i'll give that a try and see what happens.

[james250]

ok, so i tried with the old MAF and no difference still the same. so got a second hand throttle body from a 56k miles car and swapped that out. Still hasnt solved the problem although with the new throttle body the car seems to idle better. but the mpg seems very low and is climbing so i guess i'll wait and see how that goes.

but the main problem with the random power lag still persists. i recorded data from the OBD port for a little while and the fuel trims seem to dance around alot, is this normal. also since this problem occured, one thing in particular i have noticed is that when i rev high to pickup it stutters at just below 2k rpm and then all of a sudden goes up and holds on the gear longer and as a result the rpm goes very high. before this problem occured although it used to hold on lower gears when i pickup quickly it wasnt for as long as it is now. It almost feels as if there is something wrong with the vaccum lines, but i checked and cannot see any leaks. Another thing i noticed is that the intake noise changes slightly when this problem occurs.

any help and advice would be much appreciated. i might have to take it into the dealers to check it, but my concern is that it's not a problem that occurs very often and is very intermittent and wondering if the dealers will be able to find the cause

[ColinBarber]

it does sound like it could be a vacuum leak but I wouldn't expect it to be so intermittent.

The next thing I would look at are the sensors. Accelerator position sensor, throttle position sensor. Not sure if the IS250 has both of those or if they are built into the throttle body, but they may need adjusting.

[james250]

it does sound like it could be a vacuum leak but I wouldn't expect it to be so intermittent.

The next thing I would look at are the sensors. Accelerator position sensor, throttle position sensor. Not sure if the IS250 has both of those or if they are built into the throttle body, but they may need adjusting.

I assumed these were built into the throttle body as I couldnt find any other sensors around that area, so hence why I replaced the throttle body. I've got a Joe-Z intake with a modified lower section air box to get the growl noise which usually can be heared above 3500 rpm, but when this problem occurs, i cannot hear this growl intake noise, the intake noise is just so low and sounds like i'm only revving on the lower band yet the rpm display is showing above 5000k but still no noise. The only sensor i noticed near the throttle body is the vacuum switching valve, not sure if this can be anything? the problem is so intermittent that i can never replicate the problem, it just comes whenever it wants.

Any other suggestions?

[james250]

So I finally got a Check engine light come on today and scanned the code and it read:

P2714 - Pressure Control Solenoid "D" Performance/Stuck off

Any ideas on what this is?