would the EGR cause idle to surge? I have an EGR code and my idle is at 1500 until it warms up..

 

I have an EGR code as well but that in the past for me has always made the idle drop or stall.

 

I hate to say it but im in the same boat and ended up sending it in to the dealership and they think it is the ECU

My symptoms
High Idle (1500-1700)
No Power
No Code but check engine light on
Running Rich as can be

 

Well after replacing all the vacuum lines (and I mean every single one of them) the EGR code is gone so there was a tear somewhere in one of those but it still idles at 1500 RPM.

We hooked the Lexus Dealership's ODB1 reader up today and no codes (nor a CEL, so we're good there).

I've got plenty of power (in fact took it up to 130 MPH on the way to dealership today) and the car runs the best it ever has but it's just idiling high.

I think the TB gasket is toast, the IAC hole may be messed up on it allowing air to go right past the seal the IAC makes so it just idles high.

I have the Lexus Tech friend of mine replacing the mounts right now (Supra TT Mounts) and he's going to take a look at it.

 

If anyone wants a video description of the IAC and how it operates (plus the internals).

http://gallery.me.com/epelezo#100018...&bgcolor=black

 

Well, I think we figured it out.

The TPS was specced out to .75

Unscrewed it and dropped it all the way to the opposite side, and reset the ECU.

Idles fine and drives fine. I'm pretty sure the TPS is bad, I'll buy a set of feeler gauges tomorrow and use my digital volt meter to ohm it out to verify.

On a positive side note, Supra Motor Mounts installed. A+ - For those worried about Lexus vibration reduction, no issues with Vibrations.

 

Can the TPS cause the IAC to go up too far? The idle went back up again and the only thing I did was turn the tps. I immediately put it back and reset the ecu and the idle remained high.

 

I need pictures ASAP (preferably from two different cars).

1) Your TPS setting (both top and bottom screw)
2) Your Timing Setting [the lock nut behind dizzy]
3) Your throttle body linkage (I know, sounds dumb, but I think it may be binding on the downward snap).

 

Hahaha, I just had the throttle body off after taking everything apart again and sucked on the vacuum hose to the diaphram for cold start. It wouldn't let the throttle plate drop past a point.

I cleaned what little carbon was left (and I mean LITTLE) and guess what happens? I hit the throttle with my hand and the butterfly drops back to the RIGHT spot (while still holding the diaphram arm away from the throttle).

Moral of the story, if you clean something, you damn well better do it perfect.

I'll take a video and show you what I'm talking about here soon, if it works anyway lol

 

Hope it worked. If you still need pictures, I took some, I can post.

 

Actually, I went to the junkyard today and found the first SC300 to be in my city, ever...so I demolished that car in snatching parts (everything from ECU to AC unit to the freaking cluster - did I mention it's a 5 speed ).

It happened to have an IASC and TPS on it...

I tried the TPS first, my idle was sitting at 800 RPM's on the way to Best Buy. I don't know if it's permanent yet, I had a false alarm yesterday on a "fix". We'll see...

 

Did you rape the tranny from it?! hahaha
I could really use one!

 

I'm going to soon, along with the clutch pedal, etc - I may have a five speed swap waiting to go whenever boost comes along and I grenade the stock transmission (if I even wait that long).

--

Back to the subject at hand, I'm pretty sure I can now tell you what the problem is.

A ground...

Yes, the left main ground that splits off into four wires on the Lower Intake Manifold was corroded from the water.

I assumed the TPS was the fix, but that was until I got home and "touched" the TPS harness and I noticed it was tight against the ground. That's when the idle shot up, and I took off the bolt, cleaned it, and put it back on - idle drops.

I should have seen this from a mile away, it smelled like it was running rich, the idle was high, the IAC worked (sometimes) - all signals of a ground failure.

D'oh

If anyone gets bored and wants to get out a digital meter and check the Ohms to each ground point I would be forever grateful. I wonder if people realize the importance of these whenever they move stuff around / modify the engine bay. The rear strap on the head that goes to the firewall is LAYING on the transmission (this weekend I'll fix that one).

Total Amount Wasted:

$50 Carb Cleaner & Elec Cleaner (I went through a LOT - cleaning up the engine bay too).
$50 IAC - hasn't even gotten here yet
$175 Parts - Full Throttle Body, IAC, TPS, etc from Junk Yard Car
1 Week Of Absolute Head Scratching & Banging - Priceless

 

so you trying to tell me that 1 ground that wasn't making good contact caused the TPS and/or the IAC to malfunction and cause the idle to raise to 1700 rpms?

question: does the car stay steady at 1700 rpms or after warming up a little it bounces up and down like a Honda with a bad o2 sensor?

 

That's correct - one bad ground is actually FOUR bad grounds (ironically to each sensor on the UIM/TB).

It did not bounce up and down ironically until I unplugged the IAC whenever the car was idling right (before I discovered the ground issue) which is why I assumed it may be the IAC or TPS.

The ground that I speak of goes to the TPS, IAC, ECT Coolant Sensor, Coolant Sender Sensor.

My car would cold idle just fine, but when it went to drop down it wouldn't. It would stay at 1200 - 1500 RPM without any issues.

It actually makes perfect sense. The IAC depends on 4 grounds internally to be activated in sync to idle down. The ECT sensor needs a ground to tell the computer what the coolant temperature is.