high idle, runs fine. low idle, misfire

[Supraman1313]

I have an '87 supra na, 5spd, with only a k&n cold air intake mod. The car has a high idle (about 1800rpm) and it doesn't matter how long the car runs, it will idle at 1800. I adjusted the idle down to 1500 and it sounded good but when I got to 1000rpm it sounded like it was misfiring. What could cause this if I have no problems at rpms over 1500?

I haven't had the chance to do general maintenance to the car yet. I just picked it up two weeks ago. I want to change the oil, plugs, wires, rotor and cap...etc. Change all the fluids and other general stuff. But in the mean time, what is causing this misfire?

Thanks in advanced,
Larry

[AJ'S 88NA]

I have an '87 supra na, 5spd, with only a k&n cold air intake mod. The car has a high idle (about 1800rpm) and it doesn't matter how long the car runs, it will idle at 1800. I adjusted the idle down to 1500 and it sounded good but when I got to 1000rpm it sounded like it was misfiring. What could cause this if I have no problems at rpms over 1500?

I haven't had the chance to do general maintenance to the car yet. I just picked it up two weeks ago. I want to change the oil, plugs, wires, rotor and cap...etc. Change all the fluids and other general stuff. But in the mean time, what is causing this misfire?

Thanks in advanced,
LarryHow did you adjust the idle? It's controlled by the ECU.

Checked for codes? There are several things that can cause high idle from vac leak to bad temp sensor, ISC, etc.

Check the TSRM

[Supraman1313]

I don't have a TSRM, haha. I simply adjusted the idle speed screw right at the throttle plate. I haven't checked for codes nor have a way to do so just yet.

[AJ'S 88NA]

I don't have a TSRM, haha. I simply adjusted the idle speed screw right at the throttle plate. I haven't checked for codes nor have a way to do so just yet.

That's not a idle screw. The TSRM is here on line. It will also tell you how to check for codes, so you do have the way to check them as long as you have a paper clip or piece of wire.

[Supraman1313]

That's not a idle screw. The TSRM is here on line. It will also tell you how to check for codes, so you do have the way to check them as long as you have a paper clip or piece of wire.


Where can I find the TSRM that you speak of? And thanks for the info.

[AJ'S 88NA]

Where can I find the TSRM that you speak of? And thanks for the info.

http://cygnusx1.net/Supra/Library/TSRM/MK3/

[Supraman1313]

thanks

[Supraman1313]

my buddy (who we call "master mechanic") told me it's most likely a vaccum line. So I'm going to break out the brake clean tonight and see what the problem is.

[AJ'S 88NA]

I don't have a TSRM, haha. I simply adjusted the idle speed screw right at the throttle plate. I haven't checked for codes nor have a way to do so just yet.
There is no idle adjustment for the GE. It's controlled by the ECU. What ever screw you adjusted, I think I know which one, you need to put it back were it was. If it's the little screw down at the base of the TB, that has to be adjusted right or your TPS is going to be wrong.

[supraman508]

my buddy (who we call "master mechanic") told me it's most likely a vaccum line. So I'm going to break out the brake clean tonight and see what the problem is.speaking of vaccum.i have this hissing sound near my E.G.R vacum modulator.could that also mean my modulator is gone BAD.:eek3:panic,l.o.l

[sneakypete]

prob means you have a vac leak

[Supraman1313]

ok, i changed my engine oil and tranny oil with royal purple brand, shifter bushing, spark plugs (ngk), wires, cap, and rotor. and yet no change with idle and sputter at idle. the old spark plugs looked like its running rich. the car runs great above 2000rpms but now idles at 1500rpms. i have two wise mechanics telling me its my cold start injector failing, which could make it stick open spraying fuel. is there anyother wise mechanics out there who can add some input. knowledgeable people only, please.
thanks,
larry

[KongGMC]

You've actually got 6 injectors on there. Not a primary and secondary which I think is what you're talking about(like on the older TBI chevys). Not sure what is causing your problem but I have the exact same car which had the exact same problem. I had a blown head gasket so I tore it down and I have found OODLES of problems. Nearly clogged fuel rail, mostly clogged EGR ports in the intake manifold, slightly stretched timing belt, etc, etc. I would try set the "idle screw" you speak of back where it was like the other guys are saying, then get a timing light on that thing. When I first got my car the timing was adjusted to something like 30-35* before TDC instead of 10* where it should be. This helps to mask the missfire at idle problem and was also helping to restore quite a bit of lost power due to whatever actual problem causes this. Good luck with it..... God knows I need help with mine, LOL!

[Supraman1313]

actually there is a cold start injector along with the six injectors. it sprays fuel when the engine is cold and if it fails it could cause it to stick open giving me a higher idle. speaking of being higher, anyway, thanks for the input

[KongGMC]

Oh... could you tell me where I might find it cause I have my engine torn down to just the block and bottom end internals and I can't find it mine. ;P

[AJ'S 88NA]

Oh... could you tell me where I might find it cause I have my engine torn down to just the block and bottom end internals and I can't find it mine. ;P
It's mounted on the intake and has a fuel line going to it. You can check it with a ohmmeter, suppose to read 2-4 ohms.

[KongGMC]

Could you possibly show me a pic of it? I seriously have my whole intake torn apart on a bench and have not seen this.

[AJ'S 88NA]

Could you possibly show me a pic of it? I seriously have my whole intake torn apart on a bench and have not seen this.
TSRM, EFI system, Cold Start Injector. A link to the TSRM is in the stickies at the top of the GE tech discussion page don't you know:)

[Supraman1313]

go buy a haynes supra manual, its cheap and has pretty good info. when you do its on page 4-17. what year supra?

[Supraman1313]

ok, so i checked the resistance of the cold start injector and i got 3.5 ohms, so that's good.
so then I checked my engine trouble codes. I got 21 (oxygen sensor signal) and 51 (air conditioner switch or neutral start switch signal).

I'm gunna pick up a new O2 sensor later this week and see if that solves the problem.

Anyone know what to do about code 51??

Thanks,
Larry

[supramacist]

Dis-connect the battery for 20 minutes and don't even touch the throttle while you're pulling codes. See if that gets rid of it.

[ToyotaFear]

Code 51 is your TPS. Probably from adjusting that "idle screw" as you put it. If its the screw I'm thinking it is(throttle stop screw) than you need to adjust it. Back out the throttle stop screw until you see space between it and the throttle lever. Then bring the screw in until it touches and tighten the check nut. See the TSRM for details.

http://www.supramania.com/forums/showthread.php?t=46793&highlight=remove+throttle+body

[AJ'S 88NA]

Code 51 is your TPS. Probably from adjusting that "idle screw" as you put it. If its the screw I'm thinking it is(throttle stop screw) than you need to adjust it. Back out the throttle stop screw until you see space between it and the throttle lever. Then bring the screw in until it touches and tighten the check nut. See the TSRM for details.

http://www.supramania.com/forums/showthread.php?t=46793&highlight=remove+throttle+bodyAlready been pointed out, read the whole thread:)

[supramacist]

The code 51 is like an audible code. The diagnostics will stop flashing it when you get it tuned out. And then you reset and adjust the timing.

And if it's being covered it isn't being covered enough. Surely I'm not the only person noticing a rash of vaf and tps codes being throne up lately. The vaf's are norm but the 51 is off the charts.

I wonder if this could have anything to do with climate sensitivity brought on by a flux in seasonal change.

[Supraman1313]

ok, so I replaced the O2 sensor and at first it did nothing. So I drove it for about a mile and then came back to it an hour later, started it up and the idle came down from 1500 to 750 in about 10 seconds but then after a few more seconds it slowly started to idle lower, down to 500rpm and running rather rough. I gave it some gas and she started idling at 800 and was fine. I tried it again and she idled down to 500rpm, after a few seconds it starts to come back up to about 800rpm. The car runs perfectly fine when i'm not idling. This weekend I plan on taking out my intake manifold and shit and clean it all.

Any suggestions??

Oh and code 51 came up because I had it in gear...haha.

[Finnon]

hmm its probably nothing to do with your fault but i had a high idle on mine >1200

i tried a few things. cleaned up the csi and the iscv i fitted new plugs plus a variety of other things. nothing changed it. then i swapped the ecu's over and it cured it

[Supraman1313]

well like i said, this weekend i'm just going to take a bunch of shit out and clean them up.

[Supraman1313]

Ok, so I picked up a new throttle body to intake manifold gasket from a Toyota dealership (I know, more money, but it's the real deal. plus I got a discount that made it worth it). And so I took my throttle body off, used a toothbrush and cleaned the whole inside and vac holes. Turns out one of them were clogged. Clean up a couple of pipes and stuff and put it all back in. I turned back the "idle screw" and started her up and oh man, she purrs at 700rpm (I think a little low, but it works). BUT, she still misfires a bit at lower rpms.

Could my timing be off? I can't see any problems with the ignition cuz i changed the plus, wires, cap, and rotor. Any ideas??

[AJ'S 88NA]

Ok, so I picked up a new throttle body to intake manifold gasket from a Toyota dealership (I know, more money, but it's the real deal. plus I got a discount that made it worth it). And so I took my throttle body off, used a toothbrush and cleaned the whole inside and vac holes. Turns out one of them were clogged. Clean up a couple of pipes and stuff and put it all back in. I turned back the "idle screw" and started her up and oh man, she purrs at 700rpm (I think a little low, but it works). BUT, she still misfires a bit at lower rpms.

Could my timing be off? I can't see any problems with the ignition cuz i changed the plus, wires, cap, and rotor. Any ideas??If you haven't had a timing light on it you need to. Follow the TSRM to time it with a jumper wire. And did you set the stop screw back according to the TSRM?