Rough Idle Issue

suprajim · 12-19-2009, 12:02 AM

Ok, so it is too dark to really mess with the car right now, but I had unplugged the ISC valve electrical connector while the car idled and there was no change in behavior....still idling erratically. Could this alone point to a bad ISC valve or could the TPS still be a potential cause?

cre · 12-19-2009, 08:37 AM

Any diagnostic codes stored in the ECU?
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx

TPS Calibration:
http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=101

ISC (Idle Speed Control) testing:
http://www.cygnusx1.net/Supra/Librar...ction=FI&P=106

More testing, less guessing.

suprajim · 12-19-2009, 02:42 PM

Ok, sorry if these are stupid questions, but I want to be sure I do this right. Do I need to have the engine running when I test the TPS? Secondly, how do I apply "battery voltage" to the ISC valve? Do I just run a short wire from the battery?

MA70-3.0GT · 12-19-2009, 03:25 PM

If you take a bit of time to properly read through the tsrm links cre provided you'll find it answers your questions... More haste = less speed as they say, stop trying to rush through without researching properly as I suspect you're doing & you'll find it's a half hour job!

If I'm honest the isc test is one you can usually skip provided you can hear it resetting (clickclickclickclickclick) after engine switchoff, just make sure it's clean inside & the one way valve isn't held open by any bits of rubbish...

EDIT-: and I assume you have no codes stored? That's obviously the first thing to check.

cre · 12-19-2009, 08:43 PM

Hell, the car may still not idle properly once the original problem is fixed due to the manual adjustments made. In this case the idle is usually just very high but reasonably steady.

suprajim · 12-19-2009, 10:35 PM

Ok, so I had just checked the resistance of the TPS and I kept getting about 7K. I followed the instructions to the T and inserted the .7mm feeler blade and loosened the screws, turned clockwise and the needle of the ohmmeter never deflected and constantly stayed at about 7K. So, am I doing something wrong or is my TPS bad? I'm sorry if I seem like an idiot, but I am trying to learn. I've done many other mechanical jobs on this car, but these sensors and electronics are new to me. Thanks again for the help. As a side note, I checked again and still only have code 21 which the car has had for the 2 months I've owned it, even after replacing the O2 sensor and pulling EFI fuse and battery to try to reset.

12-19-2009, 12:02 AM	#1
suprajim Intake Join Date: Jul 2009 Location: Dallas, TX Posts: 36	Ok, so it is too dark to really mess with the car right now, but I had unplugged the ISC valve electrical connector while the car idled and there was no change in behavior....still idling erratically. Could this alone point to a bad ISC valve or could the TPS still be a potential cause? __________________ 1992 Supra 7MGTE A/T w/Sunroof Super Red/Shadow Gray

12-19-2009, 08:37 AM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Any diagnostic codes stored in the ECU? http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx TPS Calibration: http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=101 ISC (Idle Speed Control) testing: http://www.cygnusx1.net/Supra/Librar...ction=FI&P=106 More testing, less guessing. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

12-19-2009, 02:42 PM	#3
suprajim Intake Join Date: Jul 2009 Location: Dallas, TX Posts: 36	Ok, sorry if these are stupid questions, but I want to be sure I do this right. Do I need to have the engine running when I test the TPS? Secondly, how do I apply "battery voltage" to the ISC valve? Do I just run a short wire from the battery? __________________ 1992 Supra 7MGTE A/T w/Sunroof Super Red/Shadow Gray

12-19-2009, 03:25 PM	#4
MA70-3.0GT 12psi boost Join Date: Oct 2009 Location: Crewe, England Posts: 356	If you take a bit of time to properly read through the tsrm links cre provided you'll find it answers your questions... More haste = less speed as they say, stop trying to rush through without researching properly as I suspect you're doing & you'll find it's a half hour job! If I'm honest the isc test is one you can usually skip provided you can hear it resetting (clickclickclickclickclick) after engine switchoff, just make sure it's clean inside & the one way valve isn't held open by any bits of rubbish... EDIT-: and I assume you have no codes stored? That's obviously the first thing to check. __________________ '89 MA70 Supra GT aero 3.0turbo JDM, Rebuilt motor, K&N intake, 3" stainless turbo-back. New turbo and braided line kit... '89 Honda NC27 400, NC23 cams, open pipe, PC36a shock & possibly Showa USD forks... '83 Yamaha 29R XJ750E-II, number 69 off the line, only runner in the country? Original except Koni shocks '95 Honda PC26 CB500R, Winter hack, hateful, trying to sell it I'm not paranoid, they really ARE after me!!! Last edited by MA70-3.0GT; 12-19-2009 at 03:35 PM.

12-19-2009, 08:43 PM	#5
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Hell, the car may still not idle properly once the original problem is fixed due to the manual adjustments made. In this case the idle is usually just very high but reasonably steady. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

12-19-2009, 10:35 PM	#6
suprajim Intake Join Date: Jul 2009 Location: Dallas, TX Posts: 36	Ok, so I had just checked the resistance of the TPS and I kept getting about 7K. I followed the instructions to the T and inserted the .7mm feeler blade and loosened the screws, turned clockwise and the needle of the ohmmeter never deflected and constantly stayed at about 7K. So, am I doing something wrong or is my TPS bad? I'm sorry if I seem like an idiot, but I am trying to learn. I've done many other mechanical jobs on this car, but these sensors and electronics are new to me. Thanks again for the help. As a side note, I checked again and still only have code 21 which the car has had for the 2 months I've owned it, even after replacing the O2 sensor and pulling EFI fuse and battery to try to reset. __________________ 1992 Supra 7MGTE A/T w/Sunroof Super Red/Shadow Gray

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