p1fcl01

My RX now jerks or shudders around 55mph most of the time and gas milage from ususal 17-18 down to 13-16. When I put car in park, the rpm is around 750 but it not stable, it will drop a few then back up like idling not properly. I did use Lexmex method of cleaning the ICV and the MAF. No ECL on yet. The gas pipe fume does smell a bid stronger or heavier smell, smells like a strong mix. I will dump 2 bottle of Techron tonight and fillup the tank and see what different will make. Anyone have any idea please let me know. Thanks in advance.

Frankie

Lexmex

Where does the jerking or shuddering feel like its coming from?

Meetya

This sounds like A/F Sensors.
1. Open the fuse box. And check A/F Heaters fuse. It is a 25A fuse (see attached picture).

2. Check A/F Relay. Swap it with Horn Relay (they are interchangeable) and check if your horn works. These relay are black medium size boxes (3 black things on left on the picture and 1 on the right).

2. Check their A/F Heaters. For each sensor disconnect A/F sensor harness -- It has 4 contacts, two are gold and two are silver. Measure resistance between silver contacts, it should be around 1 Ohm. If it is short (0 Ohm) or open (infinite resistance) you need to replace them.

More info in this thread:
https://www.clublexus.com/forums/sho...=288374&page=3

Location of A/F Heaters Fuse:

TunedRX300

Did you get a Check Engine Light? You can get free code read at Autozone if CEL is on.

Meetya

I bet he has pending P0125.

TunedRX300

Possible, but when my A/F sensor for bank 1 was gone, no P0125. Just two codes indicating that senors are bad and the usual accompanying codes of system too lean and too rich.

Meetya

Yes, usually P0125 or P0171/P0172.
Btw, your profile says you have "2000 RX300 AWD MSM". What does MSM stand for? Tried searching, found this:

TunedRX300

Millenium Silver Metalic. You remind me to update my signature to include mods that I added this year.

Lexmex

MSM= Mean Super Machine

TunedRX300

I thought that was reserved for your Black Bull. I am ordering Tom's Radiator Cap from Carson Lexus to make it meaner

Lexmex

That should go really well with the TRD T-Stat.

I love cooling mods.

p1fcl01

Sorry for late reply, training some new workers.

btw, the jerking is like the car studders, like right under my seat. very hard to explain. all i know is that sometime when the car hits 60mph and then i let go of the gas a little to around 55mph, that's when the car shake forward and backwardm if that's call jerking or studdering. my co-worker just told me that he expericence similar on his 4runner and it was piston misfire, hope this is not my issue. i will do the fuse switch test, but how do i do the resistence check, is it silver to silver and if 0 or infinite, then replace. which one i need to test, all?

btw, the engine light did come on as p0171 becuase the o2 sensor under the seat, that would be after the cat, fell off. I had a guy cut those bolts and replace with new one, cost me $100, well it's a lot, but he has the tool and I don't and $100 I can afford for now.

Also, I found some fairly new tires 500 miles on them, RX330 17" factory 6 spokes with Michelin Energy LX4 225/65R 17 101S M+S, 5 full rim and 5 tires, one brand new. take offs, for around $600 shipped, good deal or not? Would it fit my 1999 RX300, I think it will, just a +1 setup, right?

Thanks

Lexmex

I could theorize how this could be misfire related. When I was experimenting with that recent intake modification (I removed it) I had issues where when I would pull of gas at high speed (right around where you are talking about) it would jerk back...no CELs, but I could definitely tell too much air before the closed throttle body butterflies (and not into the exhaust manifold, where the A/F sensors would trigger the CEL). In the case of a misfire, the air would get backed up (since it wouldn't be part of the combustion). In addition, that strong smell out back on the exhaust, unburnt fuel.

However, this again begs the question that a misfire code should be picked up.

Meetya

I know how that jerking feels. In my case it was jerking on high speeds in lower RPMs (2500-4000). If you floor the gas, jerking goes lighter. Right? Try to turn off O/D, while driving 60 Mph. I don't think that it somehow related to misfiring.
Measure resistance between two silver contacts for both sensors before catalyst. Do you know the locations of both sensors?
Also, I am very sure you have codes, but they are in pending conditions. You can take your RX Autozone, explain the situation and ask them to get PENDING codes. Or just buy a simple OBD-II scanner, they have it for $59 right now. Or just drive for a while until CEL comes on, it could be another 100 miles.

So are you saying that you have P0171 right now?

Meetya

No, this is a different kind. You experienced a single push, while if the engine is chocking on air, it would be like very uncomfortable continuous shaking back-and-forth until you increase RPMs. And you can smell gasoline while standing on a traffic light.