Hey guys, first post here and was hoping it wasn't a problem post but alas here I am. I'll try to be as clear and concise as possible to narrow down my problem I desperately need help with.

Just bought a 2006 Lexus IS250 with 190k kms on the clock.

Finished up servicing the car and last thing I had to do was spark plugs. Removed the two ECM and ECU fuses.
Used Denso Iridium TT Spark Plug IKBH20TT they're pre-gapped from my knowledge and ready to go out the box.

Cleaned intake heads with a rag as well as replaced intake gaskets and gave everything I could see a wipe down due to the carbon sludge in the engine.
Decided to clean the throttle body while I was there as it was dirty. Used degreaser sprayed on it pretty generously (Dumb I know). Also moved the actuator, throttle body plate with my hand ever so gently a couple of times to clean the tops and the cylinder properly. Some videos say you can do this, others say dont because you could damage the gears.
Didn't replace the PCV but gave it a good clean with degreaser also and allowed to dry.
Put everything back together meticulously and made sure every connector was right.

First start. Car heats up to operating temperature fine while in park. Hits around 900 rpm and says there. Idle is great. Took it for a drive and drives like a dream no worries. Here's were the problem starts.
First time starting after turning the engine off in park. I immediately get thrown the P0505 (Idle speed control system malfunction (ISC)) and the engine just sounds the tiniest bit off in its idle and you can feel it in the drivers seat ever so slightly. VSC warning and engine light now flashes on the dash. (I'm guessing this just gets flashed due to the code and there's nothing wrong with the vsc system). Car drives fine, idles poor.

After some testing and troubleshooting of when exactly the code appears and after what sequence of events occur I've come to the conclusion that it happens once the car is put into park at operating temperature. I found this after clearing the codes while the acc on engine off, starting the engine and immediately putting it in drive. I can drive the car normally, stop, with the break at lights/parking but the second i put it into PARK it'll throw that code and begin to idle poorly while idling fine when stopped in DRIVE.

I've done a lot of trouble shooting which I'll now list.
Resetting the ECM so many times to relearn the new idle
Cleaned MAF sensor with MAF cleaner
Gone over throttle body and cleaned again
Small test for vacuum leak using carby cleaner
Checked harness for TB and moved wires to check connection
Disassembled the entire intake plenum again in-case of vacuum leak/gasket wrong etc

Next steps if I can't fix it:
Replace throttle body
Replace MAF

Pulling my hair out on what it could be. I've scoured this forum and google for anything that could lead me to the answer but can't seem to find it.
The ISC from what I know is inbuilt into the side of the throttle body for the IS250 correct? So is it possible I've damaged that with the degreaser or moving the plate with my hands?
The car runs fine other than idling. Also the throttle body is at 14.5% isn't that perfect? Also idle RPM isn't that erratic but I can still hear the car perform poorly and shake a little while im in the seat.
I've attached screenshots of the sensors of my car at idle, at operating temperature and in park for any of those that could help diagnose what's happening.

At this point I'm happy to try anything, even a ritual sacrifice to get this thing to be normal again
Any help would be much appreciated and I'll provide as much info as you need.
Thanks for reading!

 

The only thing I see off is maybe the MAF it should be reading near engine displacement. 2.5L MAF should read 2.5 g/s.

Does is remain high at 3.0 g/s? While idle reving the engine does it come back to around 2.5 g/s?

 

Hmm, it always remains at above 3.1 g/s no matter what. Something I should look into?

 

Just out of curiosity, where were the spark plugs obtained?

 

When you mentioned pulling ECM fuses to start plug change. You didn't unplug the negative side on the battery?

Also you didn't mention if the car stalled after the first start. This happens at every ECU reset if done correctly. I'm thinking it was never offline while pulling the fuses. So you pulled the 10, and 25 from fuse box to be correct?

I've yet to see the spark plugs gapped to spec. Always check anyway get a cast disk gap tool, but you will need a micrometer to check at what tick mark you need. Most likely it will be a little off.

Last are you sure you checked for cracks on all vacuum lines? At 190k most will be hardened, and easily crack at the nipple possibly splitting. You mention a little rough idle. It's probably carbon build up. As for the MAF it should be around 2.5 g/s, but at 3.0 g/s the throttle body is slight just open trying to maintain idle.

Did you fully remove the TB from manifold, or just open the butterfly to clean it? It's rare these TB's go bad. So I would just carefully inspect vacuum lines. Purge vavle not sticking open. It's the one line that runs under the intake pipe. Make sure it isn't disconnected from the hard line on the body. To test the purge valve while car is on remove connector, and and pull the hose there should be no suction from manifold.

If it was running well with no lights on before you got in there. Then definitely retrace your steps.

 

Cheap from a wholesale in Australia that do sell genuine parts from what I know. I did double check to see if they were fakes. Nothing I noticed going by the Denso video on youtube.
Why do you ask? Could it be causing issues like this?

When doing the spark plugs I just disconnected the battery. Then while doing everything else trying to solve the problem I just disconnected the fuses and yes 10 and 25.
Going by this https://www.clublexus.com/how-tos/a/...our-ecu-363500 Do I have to do both at the same time? It does say one or the other. And the car does not stall after I reset the ECU.

Hmm, maybe I should pull them and gap them to spec then? Car seems to run fine other than the idle issue and code.

I checked the vacuum lines and they seem to be a little cracked around the top (see attached pics) same with the pcv hose at the back but its really not that much at all.

Interesting about the MAF sensor, wonder why it could be pulling in that much, the carbon build up on the tops of the hats were yuck. And yeah the idle is just a little off but nothing particularly bad. Its just that the codes and the VSC flashing put me off and make me want to try and fix it because it wasn't doing it before -_-

For the throttle body, I removed it minus the coolant hoses and cleaned the back and front plates all clean. I'll have to check the purge valve could you help locate it and I'll test it?

I do really appreciate the help you're giving me

 

The hoses look ok at the ends, but you dont want them splitting. Make sure you readjust the clamps to get a good bite. Don't set them back into the previous indented marks. So to be sure your engine light is flashing? Along with the slip indicator, or actual VSC?

If the engine light is flashing then there is a misfire. Did you check connections on the COP's = coil packs. Did you notice any oil down in the spark plug tubes while changing plugs?

And yes if the car is not stalling the first try the ECU has not reset. Pulling the ECU fuse's 10, and 25 for two minutes. As for battery negative disconnect 20 minutes should be sufficient.

The last picture you posted with the vacuum hose that is the purge valve. Pull the inlet hose side from under intake. Disconnect the 2 wire harness. On that port disconnected no vacuum from engine should be sucking as the valve should be shut closed disconnected.

 

Thanks for getting back to me!
I have been putting them back into the indented old places so I'll try and re-adjust all of them.
The engine light does flash once the VSC gets thrown, does not flash unless the VSC comes up. The VSC will appear randomly once the code is thrown after a couple of minutes after the car reaches operating temperature at idle.
I put anti-seize and dielectric grease around the bottom of the coil packs and on the porcelain bits of the spark plug. The old plugs didn't have much oil on them just carbon build-up.
Surely if there's a misfire it runs poorly even when not at idle? Also would tell me on the scanner?

Hmm, this is an odd one. Could it be different in the US, I'm in Australia and the engine is a little different with some of the hoses. It sounds like maybe I haven't properly reset the ECU, but then again, the lexus touch screen seems to boot up into the startup loading screen once I've done it.
Just to be clear, I don't have to do both at the same time. I can either pull the fuses for two minutes OR disconnect the negative terminal for 20 mins. I let both sit over night disconnected so lets see if it stall right away. Also should I be starting the car straight into turning the engine on? Will that matter?

Oh I see, I'm on the right track though right?

This is such an annoying problem. I might have to do a smoke test because everywhere points to a vaccum leak I just can't hear it and carby spray doesn't do anything.
I did change my air filter to a ryco one so maybe thats doing something to the MAF air flow at idle. I'll try that today too. I'm keen on finding this problem and again I appreciate your help with things.

EDIT: I saw you added the extra bit at the end to help with the inlet hose. Is it this connector you're talking about, I can't see the second harness you're talking about? Ive included the picture of the engine you could maybe show if its not the right one? Sorry for the questions
EDIT 2: I found this connector that wasn't seated right. Will report back with results from moving it while the engine is on.

This hose and this harness? Is there another harness ?


Just found this connector that wasn't seating right.

 

Yes that's the purge valve connector. Since you mentioned you used antizeize, and dielectric grease on the plugs. Using too much is not good. I've never had to use it on any car I normally have serviced. Just drop new plugs in bone dry, torque and call it a day.

If it were me I'd pull the plugs out again, and try to clean the plugs, and coil pack boots. You don't want any on the coil spring contact to plug. Using too much on the plug thread's it will reach the electrodes, or make its way to the spark plug gasket. That's just me though.

As for the filter is it a high flow paper filter? Typically the OEM type filter is the best for these cars. It's more than enough for a stock engine. Yes it doesn't matter one or the other ECU reset as long as the car stalls first try it should be good. Like you said maybe the Euro version is different. On your scan tool look at the Long Term Fuel trims they should be at 0 until fully warmed up engine. Like you mentioned before the car was running good. The problems arose after the service. Agin this is just me I'd start all over, and take my time to make sure all hose clamps are nice and tight slightly moved from previous indented position. Well before that make sure each connection doesn't have pulled wires. Then proceed to vacuum lines.

The spark plugs are 18 ft-lbs torque the upper intake manifold is best to do all 10-12 ft lbs. If over torqued the gasket might just fold over causing a vac leak. Hand tighten screws then use torque wrench in a star pattern. Then maybe one round about. Just enough so that each first turn the wrench gives indicating the correct torque is applied on the first go.

Other than that I got nothing. Sorry for the typos I spend more time fighting the auto correct feature when commenting.

 

plugs and torque specs - I used a cotton bud to coat the spark plug and boot but alas I'll re-do the spark plugs and make sure to torque the manifold to spec! Thanks for letting me know the torque specs for the bolts. I did the spark plugs originally to 13 ft-lbs due to the antiseize. And I'm sure i've over torqued the manifold just by feel.
Surely its not a spark plug issue though, otherwise i'd be getting misfires? I did a freeze frame of when the code is thrown tool which I'll add as the original post wasn't a freeze frame.

Air filter - Its not an oem part but a genuine paper filter from a well known brand in aus. But yeah I might buy the oem filter just to rule that out too and have one to spare.

ECU fuse and stalling - I did the fuses again and yes the car stalls out every time when starting! I must not have been doing it right or not noticing? Either way I can rule that out as the code still remains.

Fuel trim - Thanks I'll test that one out and report back. And yes, I know what im searching for is in front of me I just gotta look a little harder it seems.

I thought for sure it was loose wire on the vacuum solenoid valve but it seems like that even when pushed in it'll still throw the code and after testing removing it while running and or starting doesn't do anything noticeable like throw codes or effect the engine?

I'm near sure its to do with the vacuum line or PCV line or something like that. I'll keep at it.
Once again, thank you so much for the help you've gone above and beyond.

 

Double check that you replaced both fuses in the right slots. Go by the lid diagram. I accidentally placed the ETCS fuse in the incorrect slot one time when I reset my ECU. Immediate VSC error but the car was driveable.

 

Maybe I missed something here? But...... I think with the degreaser and/or other its telling you exactly where the fault is being picked up. Likely you damaged the TB ISC. That would cause all of the problems.

 

I've opened the 350 TB butterfly manually several times, biggest concern is being cut by the edge.

OP, any chance you wedged something in there to hold it open? The brass edge is very soft and can be deformed easily.

Mike what RPM does yours idle at? For the MAF to read high, it's either the idle speed from TB not closing all the way (higher RPM) or the sensor itself. The high value seems like there is no downstream vacuum leak, and more like the TB butterfly is leaking too much air.

Backing up a little, can you confirm the dielectric grease is NON-conductive vs conductive? There are two types.

Lastly, most ignition failure are under higher load like 4th 5th 6th gear but can happen at idle with fans and accessories on.

That said, if a new plug were bad, it should repeat throwing a P030n code vs a randomn code. But I would never install a plug out of box without checking the gap. Do confirm no material was lost at the ground strap or electrode.

How about the brake booster? Do you have power assist when pushing the brake pedal after sitting 24 hours?

 

Thanks my friend but wasn't the issue. Code still remains.

I've got a used throttle body on the way this week so I'll see what comes of it. have a feeling that it's not it.

Interesting that you've opened it and its fine that many times. Leads me to believe like how I imagined that it isn't the problem. I bought a cheap used one from a wreckers so I'll see if that makes a difference anyways.
I didn't wedge anything in there and the plate looks like brand new and actuates fine by hand from what I can remember.

In park the car idles at 700 - 1000 seemly random some days and in drive it'll be around 650-750 I believe off the top of my head. What does your maf read on idle warmed up?
Would that suggest that its a TB error then given the fact the Maf is reading a higher volume of air to keep the car at idle spec speeds?

The dielectric grease I used was CRC insulator grease and I applied a small amount to the porcelain and around the boot head.
I also used Denso Iridium TT spark plugs that are apparently pre gapped and aren't supposed to screwed with? But yeah surely thats not the issue if no misfires and its got insanely better as mileage?

Not sure how to test that, do you mind letting me know how?

Thank you for the message!

 

Not sure how to test what? Brake booster vacuum? If it takes two feet to depress the pedal for a start light, your booster is leaking. It could be the check valve or the booster itself.

Mine will hold for a month if that helps.

Plugs, although you didn't verify the gap, the precious metal tips (platinum, iridium) can break off.

What was the conclusion of the test Mike had you do?

How many miles and how is the car used?? If it does a bunch of short trips, it could have some carbon build up.