Ever Increasing Idle WTF! Please help

[ForcedTorque]

Symptoms:
I am having all types of problems with my idle. It starts out after cranking at about 1700 rpm, and (only)sometimes it will also pulsate during that. The pulsation will drop it to about 1200, and then back up yo 1700. Even when pulsating, it will smooth out when given fuel. It drives great, except for the idle problem. However, once I take it out on the road, the idle raises each time I stop. It increases 200-300rpm per short trip, and continues to do that, until I'm siting at a light idling at roughly3500. So, you guessed it, I don't go far.

Repair Steps:
I have swapped out my throttle body, because my TPS was found bad. I tested the new TPS before replacement, but it made no difference. I also replaced the Idle Speed Control, with one that meets TSRM specs. I want to test my timing, but my previous owner has my battery relocated to the hatch. I to rewire my entire front end, due to wiring run through a hole cut into the battery area. That is now done, but I need to get some wiring to run to my fuel pump before moving the battery. I need battery power to run the timing light.

Any ideas are greatly appreciated

 

[driftfreak]

i have the same problem.was ur motor swapped ? cause what im thinking it could be. i didnt fix it on mine eather.but it could be the harness.if ur using a n.a harness on 7mgte i heard it gives it that idling. ive checked the same things uve checked.but mine were good.

 

[Moy]

i have the same problem.was ur motor swapped ? cause what im thinking it could be. i didnt fix it on mine eather.but it could be the harness.if ur using a n.a harness on 7mgte i heard it gives it that idling. ive checked the same things uve checked.but mine were good.

Arnel, for future reference you shouldn't use "I heard" in the tech section. Definitive answers are accepted, opinions and rumors don't fly. Just so you know.

 

[TurboStreetCar]

The only way the idle could raise above 1600rpm is if the IDL contacts in the TPS are not closed. If those contacts are closed it will cut fuel to prevent idling as such a high speed. Source: Http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=125

Recheck the TPS as per TSRM here http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=101

Be SURE that at idle the IDL contacts are closed. Then the only possible explanation is if the throttle body it sticking slightly open. To test that put your foot under the gas pedal when the idle is high and pull up on the gas pedal, Or get out and push the throttle blade in the closed direction manually.

Using a N/A Harness on a turbo motor is impossible as N/A's use a distributor and a single coil, Turbos use a cam position sensor and three coils. AFM connector i believe is different, and turbos have two knock sensors.

Timing wouldn't cause and idle that high.

 

[ForcedTorque]

Thanks for the replies guys. I have the TSRM printed out, and believe it was in spec at all tests, but I will test again to be sure. My internet at home is out, and the library won't allow me to open the links, but it does sound like it makes perfect sense.

I do have a turbo harness, but it has been converted from an 89 to a 92. Could a problem there be my cause? I'll start by re-testing TPS, and report back as soon as I can.

 

[Victor Charlie]

when you modify the harness, but haven't tested it, people have to assume anything could be wired to anything, so there's no way to help you diagnose it. You should run through all the voltmeter checks for the fuel injection system in the TSRM and document the results for future reference. it takes about 2 hrs if you are slow like me. Also basic diagnostics like timing, engine codes, throttle adjustment screw settings. It's worth taking the time for a good once-over before trying to trouble shoot your problem, just to safe yourself future grief.

That said, I would think that the TPS adjustment is the most likely problem. I think I saw a sticky on it somewhere on this site, but I use the TSRM procedure.

 

[TurboStreetCar]

If the IDL contacts are properly adjusted at idle the TCCS will not let idle increase. The TPS is one of possibly more problems. Start there.

How did you convert the harness? What exactly did you touch?

 

[91Supra313]

This might help, or it might waste a minute or two of your time but I had that problem when I was removing parts to paint them on my GT Limited. I had my friend come over and poke his head around there and see if he could figure it out and he found it immediately. It was the throttle cable. Where the cable goes into the firewall, there is a protector on it. It was hanging up on the firewall. Once he pushed that back in where it was supposed to be, everything went back to normal. Give that a quick check. All I did was push the cable out of the way to get at some heat shields ( since mine is RHD) and it apparently pulled it out of there.

 

[ForcedTorque]

If the IDL contacts are properly adjusted at idle the TCCS will not let idle increase. The TPS is one of possibly more problems. Start there.

How did you convert the harness? What exactly did you touch?

Link to the thread coaching me through the re-pinning of the harness
http://www.supramania.com/forums/showthread.php?99311-89-Harness-in-92-91-90-Wiring-experts-Please!

Could someone please link me to how to test what i did? My computer time is extremely limited . This is the only thread I am seeing this time on someone else's computer. I hate to ask a lazy sounding request like that.

This might help, or it might waste a minute or two of your time but I had that problem when I was removing parts to paint them on my GT Limited. I had my friend come over and poke his head around there and see if he could figure it out and he found it immediately. It was the throttle cable. Where the cable goes into the firewall, there is a protector on it. It was hanging up on the firewall. Once he pushed that back in where it was supposed to be, everything went back to normal. Give that a quick check. All I did was push the cable out of the way to get at some heat shields ( since mine is RHD) and it apparently pulled it out of there.

This shouldn't be the problem, because it acts the same if i disconnect the linkage to the TB.

 

[91Supra313]

Ok I just wanted to make sure that wasn't part of it. Good luck and let us know what ya find.

 

[ForcedTorque]

I didn't touch the car today, because I got caught up in a house painting project that turned out pretty good. I did just find how to check the voltages at my ECU. For anyone else looking, you can start at this page, and go from there.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/FI/FI_050.gif

Tomorrow, I will get back to the TPS, and reinstall the throttle body. After that, I will embark on testing out my wiring harness terminal voltages. Hopefully my new DSL modem will show up sometime soon. These 5 minutes sessions are getting old.

 

[mkiiichip]

you can use the big wire on the alt for the pos lead on your timing light, ground points are limitless

pertaining to your problem, it sounds like your getting allot of unwanted air in the engine, but it does not mean that it is unmetered air (as it would like affect the drivibality with that much unmetered air). try pinching off vacuum lines, pcv lines, power steering idle up line anything to make a difference.

and since i can tell you like removing things so much, try using a can of carb cleaner and spray a little at a time, on specific areas that could be leaking air (vacuum leak, intake leak) if the engine idles up you have a leak.

your prob does not sound like a tps issue... start looking for where the extra air is entering the engine