Yes I agree, the engine does actually run very smoothly. The only huge problem I have with it is I have a high Output Alternator installed, but It doesn't really seem to kick in until around 600-650 RPM, when im idling at 400 my voltage drops and my battery doesn't get charged. I'm solving this problem by gettin a smaller pulley for the alternator so it's not really a big deal anymore. But since lexus did state idle RPM is suppose to be around 600-650 rpm I just want my car to be normal.

 

I rotated the tps to the right and it made the idle speed jump up to 900 rpms. I tried several times to just move it ever so slightly to the right to increase the idle and it was at 900 rpms. So I turned it back ever so slightly and the idle went back to the low 500 rpms. I couldn't get anything in between it was either too low or too high.

Before you say the tps is bad, please keep in mind I had this same problem when I had the other throttle body on with new tps sensors installed. Idle was too low to begin with and when the tps was rotated clockwise the idle was too high. I barely even moved it a mm and the idle went up to 900 rpms. I think something else is causing the low idle speed.

Also, I noticed that when the idle was around 900 rpms after turning the tps clockwise I turned on the a/c and the idle was right at 750 rpms in park. I think the idle speed in the Lexus manual states 700 +/- 50 rpms. And from what I remember reading the idle speed isn't suppose to change when the a/c clutch is engaged. So I have a low idle problem and when the a/c is on the idle speed drops quite a bit.

 

Check you EGR valve and hoses.

 

I checked the resistance of the step motor (egr valve) and it was within specs. How could a defective egr valve cause a low idle?

 

Its been a while since my idle speed was correct and I was wondering if anyone could tell me where their needle on the tach falls when the engine is warmed up and in park. (In reference to the lines marked) Since my idle speed is incorrect the tach needle drops all the way down to the first marked line. Just wondering where your tach needle falls to when it warms up completely in park (ie third marked line or in between the 2nd and 3rd mark)

 

I personally don't believe adjusting the TPS is the best way to adjust idle. Tread with caution.

 

What is the idle suppose to be in Park? and what should it be in drive?
Park: ####RPMS
Drive: ####RPMS

simple answers. Thanks.

 

i had the ecm problem. replaced that bad boy for 1k original lexus reman. but you will know for sure. if you take long trips like for 70 miles and try to get off an exit. your car turns off im pretty sure the ecm will fix the problem. you can reposition the tps but the ecm going to keep trying to adjust your idle.

 

Check your Dash Pot (DP) system. Search.

 

You can't adjust idle speed by fiddling with the TPS...at least not in an engine that is otherwise heathy (e.g. no vaccuum leaks, bad MAF, or bad MAP sensor, etc.)
All the TPS does at idle is signal the ECU that your foot is off the gas and that the engine should reduce to idle power. There is a spot (or contact) on the TPS that does this. You can see that by reading the factory adjustment procedure on lexls.com. Above idle, a potentiometer in the TPS signals throttle position to the ECU and TCU for shifting, engine timing, fuel flow, etc.
The accessories like AC and power steering need to bump up idle speed to overcome the increased load of a cycling compressor or a power steering pump that is trying to turn the wheels. They do this by admitting air directly into the intake manifold via valves...the IAV for AC and warm-up, and the idle-up valve for power steering.
This small amount of bleed air produces a small reduction in manifold pressure as sensed by the MAP. The ECU thinks the engine is idling lean and compensates by increasing fuel flow.

However, a small, but deliberate manifold "leak", like bypassing the idle-up valve "intake-to-manifold", as proposed by Och, can fool the ECU into enriching the idle mixture and raising idle speed. This technique has a drawback in that when the engine is cold, and idle speed is being governed by the IAV, this added bleed air will raise idle speed above recommended cold idle (~1200). This may not be a big deal, but at least you know what may happen.

I've been following these low idle threads and playing around with my 96 to try to solve this problem, but so far no luck. I don't have a stalling problem, and my 400rpm idle is not a big enough issue for me to invest in a new ECU. If it gets worse, I may change my mind...
Good luck.