IS200 Idle Rpm ‘STILL’ High After Throttle Body Clean & ECU Reset?

[roffstar]

It’s been over two weeks since cleaning the throttle body on my IS200 SportCross (1G-FE engine). In the morning or after a long period parked, the rpm is nearing 2000 all the time now on start up for several minutes.

 It only drops back down to regular idle speed when the temp gauge is at halfway, not before. I’ve also noticed even after driving, the idle can fluctuate and at times randomly goes up to 1100rpm even when the engine is fully warmed up and stationary. At times the idle sounds a little rough especially on cold morning starts.

I’ve driven the car daily since then so the ECU can re-learn as advised by other IS200 owners, but it’s made no difference. The rpm always shoots up to between 1800-2000 on every start after long periods of the engine not running. I have reset the ECU, replaced the Air Temp Sensor, replaced the VVTi solenoid & filter (which was broken) and carried out a vacuum leak test with no leaks found. No engine light or error codes showing on the OBDII reader.

Fyi, I didn’t remove the throttle body from the car, I just cleaned it in situ.

Is there anything else I might be missing out on diagnosing because I’m now stumped on where to look next to try resolve this? I’ve owned 5 of these IS200s in the past & have never encountered this problem with them before. This one is a 2003 model if that makes any difference.

Thank you.

[ColinBarber]

Idle suddenly jumping up sounds like a sensor acting up (or air bubbles around the coolant temperature sensor). Ideally you want to log the data from the ECU so you can see if an abnormal sensor reading occurs at the point in time when the idle jumps up.

Have you checked the throttle position sensor for calibration? 

[roffstar]

21 hours ago, ColinBarber said:

Idle suddenly jumping up sounds like a sensor acting up (or air bubbles around the coolant temperature sensor). Ideally you want to log the data from the ECU so you can see if an abnormal sensor reading occurs at the point in time when the idle jumps up.

Have you checked the throttle position sensor for calibration? 

Hi Colin, thanks for the reply. Which sensor do you think could be the one playing up, the coolant temp sensor or something else? How would I log the data from the ECU?...Can my OBD2 reader do that?  Apologies for all the questions, I'm not a pro mechanic, just a DIYer with basic mechanical knowledge.

Does the throttle position sensor need to be recalibrated when the the throttle body is cleaned? All I did was spray it with the cleaner & used a rag to get rid of the gunk on the butterfly valve. I didn't remove the body from the car nor tamper with any of the other components bolted to it.  

 

[ColinBarber]

On 10/23/2021 at 8:25 PM, roffstar said:

Which sensor do you think could be the one playing up, the coolant temp sensor or something else

It could be the coolant sensor. Being able to log the data is dependant on the software you have with your OBD2 reader and the quality/speed of the reader itself. It may be that you just watch a single sensor reading until you get fluctuation to see if the sensor reading corresponds.

You shouldn't need to recalibrate the TPS if you didn't move it, but opening the throttle butterfly has been known to cause issues in the past. Attached is the procedure for checking that calibration of the TPS and pedal position sensor.

m_fi_0037.pdf

[roffstar]

On 10/25/2021 at 9:41 PM, ColinBarber said:

It could be the coolant sensor. Being able to log the data is dependant on the software you have with your OBD2 reader and the quality/speed of the reader itself. It may be that you just watch a single sensor reading until you get fluctuation to see if the sensor reading corresponds.

You shouldn't need to recalibrate the TPS if you didn't move it, but opening the throttle butterfly has been known to cause issues in the past. Attached is the procedure for checking that calibration of the TPS and pedal position sensor.

m_fi_0037.pdf 179.84 kB · 1 download

Many thanks for the PDF.

I'm afraid I did move the throttle butterfly as I was cleaning the gunk from it. I didnt know at the time that this could cause problems. Is this something that is rectified by the recalibration or would have to do something else?

As for the coolant Temp sensor being a possible culprit, is it due to it being faulty due to age or does it have some link to the throttle body? This issue I'm having only happened after cleaning the throttle body.

[steve2006]

Also check your vacuum hoses, make sure they are tight with the clips secured and not split or damaged.

[roffstar]

12 hours ago, steve2006 said:

Also check your vacuum hoses, make sure they are tight with the clips secured and not split or damaged.

Checked the vaccum lines as you've highlighted and they're all intact. 

However, when I did the cold start, I noticed the fans kick in straight away even though the car was stone cold. I noticed this before when I first got the car and replaced the relays for the fans. Looks like that didnt change anything. Would this be another sign pointing to the coolant temp sensor?

[steve2006]

Yep all associated, if the CTS is faulty and telling the ECU the engine is cold when it is in fact normal hot it will idle the engine up to get it warmed up. For what a CTS costs just replace it.

[roffstar]

4 hours ago, steve2006 said:

Yep all associated, if the CTS is faulty and telling the ECU the engine is cold when it is in fact normal hot it will idle the engine up to get it warmed up. For what a CTS costs just replace it.

I might as well replace the CTS as I was going to change out the coolant this coming week. Would you know where the CTS is located on the IS200? I've not changed one before.

[ColinBarber]

8 hours ago, roffstar said:

However, when I did the cold start, I noticed the fans kick in straight away even though the car was stone cold. I noticed this before when I first got the car and replaced the relays for the fans. Looks like that didnt change anything. Would this be another sign pointing to the coolant temp sensor?

Not sure if the IS200 does this (it's been a while since I've owned one) but many vehicles run their fans if the AC is on - worth checking when your AC is off.

[roffstar]

UPDATE: I've since replaced the CTS, plus refilled the coolant and nothing has changed 😓. Idle is still 1800-2000rpm and doesn't go down until the engine has warmed up completely. That's about a 5-7 minute wait. I'm at my wits end with this issue now because I'm going through a lot of fuel. 

However, I do have a spare throttle body from my previous IS200. I was hoping to rectify the issue without resorting to swapping it out. Is there a link on here or elsewhere with detailed steps on how to properly install the throttle body back on? Looks like I may have to swap this one out as I've done everything else.

[bash6673]

Have you had any joy fixing this problem?

My car has the same issue. I've changed the TB, however it still takes about 5-7 mins to settle around 700rpm.

 

 

[roffstar]

7 hours ago, bash6673 said:

Have you had any joy fixing this problem?

My car has the same issue. I've changed the TB, however it still takes about 5-7 mins to settle around 700rpm.

 

 

Issue is not 100% resolved I'm afraid 😕. However, there has been slight improvement on the idling since fitting the replacement TB. After reconnecting everything (I hope you disconnected the Battery when you did the TB swap!), I drove the car around for a few days for the ECU to relearn. Could start issue was still there. I decided to reset the ECU again by disconnecting the Battery for about 15-20mins. From there the idle has now dropped to about 1200 rpm on cold starts then goes down to 700rpm in just under 5 mins. All that said, it's still guzzling fuel. 

I took it to a garage and they plugged in their OBD reader and nothing came up. They said best bet is to take it to Lexus to do an in depth diagnostic with their oem equipment. I'll wait until after Christmas because Lexus is stupidly expensive having dealt with them recently on a separate issue.  

If you have any luck, please let me know. I'll update this thread once I get somewhere.

 

[bash6673]

On 12/18/2021 at 12:36 AM, roffstar said:

Issue is not 100% resolved I'm afraid 😕. However, there has been slight improvement on the idling since fitting the replacement TB. After reconnecting everything (I hope you disconnected the battery when you did the TB swap!), I drove the car around for a few days for the ECU to relearn. Could start issue was still there. I decided to reset the ECU again by disconnecting the battery for about 15-20mins. From there the idle has now dropped to about 1200 rpm on cold starts then goes down to 700rpm in just under 5 mins. All that said, it's still guzzling fuel. 

I took it to a garage and they plugged in their OBD reader and nothing came up. They said best bet is to take it to Lexus to do an in depth diagnostic with their oem equipment. I'll wait until after Christmas because Lexus is stupidly expensive having dealt with them recently on a separate issue.  

If you have any luck, please let me know. I'll update this thread once I get somewhere.

 

Thanks for replying.👍 I disconnected the Battery before changing the TB and connected it about 30 mins later. I'm now convinced that the TB isn't the problem and I think it may be one or several of the many hoses that has a leak. The car drives perfectly apart from this problem. I've also used my OBD2 reader and there are no error codes. I think I'll have to take it to Lexus. and hopefully they'll find out what the problem is.

Thanks again for your update.

[roffstar]

11 minutes ago, bash6673 said:

Thanks for replying.👍 I disconnected the battery before changing the TB and connected it about 30 mins later. I'm now convinced that the TB isn't the problem and I think it may be one or several of the many hoses that has a leak. The car drives perfectly apart from this problem. I've also used my OBD2 reader and there are no error codes. I think I'll have to take it to Lexus. and hopefully they'll find out what the problem is.

Thanks again for your update.

Yes, it's worth checking the system for leaks. I did a leak test twice on mine & nothing came up. Please let us know how you get on at Lexus and if the resolve the problem. That way it will help others who are having the same issue. Many thanks