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View Full Version : Troubleshooting warm up idle and running rich



CollapsedNut
05-20-2016, 05:17 AM
Gen1 3SGTE. Fresh swap.
I didn't think much about it until I was texting Mafix the other day and realized something weird. I am having issues getting my idle set and it hit me, it's backwards. When I first start the car it'll just barely idle around 600rpm and I have to adjust the throttle body bypass screw to get it to idle up to ~1000rpm. But then after it's warm I have to almost completely close the bypass screw because it starts idling at 1600rpm if I don't. Once the screw is pretty much closed I still idle around 1200rpm. So it's like my warm up circuit is backwards. It's completely possible that I am using a coolant temp sensor from a 3sge or even a 3sfe because honestly at this point I have so many sensors in bags and no clue which engines they came from. Or the sensor could even be bad. I wouldn't think the sensors would really be different, but I'll probably start there. Does anyone know for sure which coolant sensor the ECU uses for this function? Other thoughts? I suppose it could be a vacuum leak too, but every hose in the bay is new with new constant tension clamps. I tested the TVIS diaphragm before I installed it, but there could be a leak from the TVIS shaft seals I guess.

donteatbugs
05-20-2016, 06:29 PM
could your iac be wired backwards?

sefiro
05-20-2016, 08:54 PM
Ecu Coolant sensor is a single wire. Back trace it to the ecu to make sure the wire isn't broken. un plug the iac during warm up to see if the rpm's return to normal. (It reduce as though you put the ecu into diagnostic mode). You can remove the iac coil and manually move the valve to check if operating correctly.

The following won't cause idle variability but should be checked to make sure minimum idle and ecu timing. Check minimum idle screw (on the throttle body where the throttle cable connects) as well as the vacuum activated idle screw that holds the throttle open at low idle. These should be set first before setting the idle adjustment screw as you mentioned. Also check the tps sensor as this tells the ecu when certain devices like egr are to be activated or not.

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CollapsedNut
05-21-2016, 03:45 AM
According to the book, ecu coolant temp is a two wire?
I finally got of my couch and came to the shop. So here's what's weird. Cold start, afr stays around 14.5:1. This time it idled at 1200 on start. Once warm idle started to drop like it should, but my afr's started to get more rich and stopped around 12:1 at 800rpm idle. Why would I get more rich once warm, that seems backwards. I just ohm'ed out the wiring and sensor to bgb specs for the coolant temp and it's in range per temperature. Idle worked this time so I may be chasing an intermittent issue here.

CollapsedNut
05-21-2016, 03:47 AM
Well I guess, maybe the afr isn't weird. Ima assume the ecu doesn't add more fuel for warm up, just adds more air to increase idle speed. Which makes sense. I'm not using a cold start injector btw.

CollapsedNut
05-21-2016, 04:20 AM
Continuing on about being way rich at idle, I just back probed at ecu and checked all the afm voltage, all in spec.

CollapsedNut
05-21-2016, 05:52 AM
Well I ran through 3 or 4 warm up cycles and it worked fine every time. So I donno.

sefiro
05-21-2016, 09:14 AM
Hhmm, sounds like a sticking iac valve. As for the afm, does it balance out during driving?

Oops on the coolant sensor. I pulled from the wrong year. You did check the sensor on the water pipe not the radiator (which controls the fan)

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donteatbugs
05-23-2016, 10:50 AM
The old ecus learn really slow. It sometimes takes a few warm ups to learn idle.

CollapsedNut
05-24-2016, 02:26 AM
I think you're onto it, cause I've been pulling my battery fuse after I'm done working on it every night. Since I've been leaving it in the idle has been right. Now I just gotta figure out why I'm running so rich.

donteatbugs
05-24-2016, 11:28 AM
Mo Money, Mo problems.

andy
05-24-2016, 02:36 PM
My 2jz takes about 10 start ups to get back to a nice start and idle. Leave the fuse in.

Murgatroy
05-24-2016, 02:40 PM
If only Chaos would learn to not drink like a mick.

She is so rich that ten minutes driving with her and you smell like raw fuel the rest of the day.

sefiro
05-24-2016, 08:19 PM
I had chased a rich condition on my 91gt for a year. Eventually tracked to micro vacuum leaks and gaskets on a number of items - vsv's, brake booster, iac, etc. Eventually fixed them all - cutting hc test by 50% and getting near New mpg.

Try deleting each item and check afm impact. You can check vsv, boosters, etc with vacuum guage/pump.

Be sure normal tuneup items are at spec - timing, idle screws, 92 sensor(another common problem).

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CollapsedNut
05-25-2016, 11:24 PM
Little update here. This is crazy. So about running rich. Normally I'm ~12:1 idle and cruise. Well I found a way to make it go to ~14 like it should be. Once warm, driving, clutch it and key off, key on and roll start it and BAM perfect 14's. But if I use the starter to crank the engine back, I'll still be in the 12's. So Ima go ahead and say something on the ST162 side harness isn't talking right to the 165 side harness when you go to the crank position on the key. Something in the STA circuit I bet. SO I brought my multimeter home, back probe leads and my box of wiring goodies. Lets see what's going on.

CollapsedNut
05-26-2016, 12:19 AM
STA circuit is good. Only powered when key is in the crank position. So there goes that idea. What else would make a difference if it sees crank vs just running...

donteatbugs
05-26-2016, 02:04 AM
the voltage drop.

CollapsedNut
05-26-2016, 03:26 AM
the voltage drop.

True. hmmm

CollapsedNut
05-26-2016, 03:35 AM
I still feel like it's something to do with my coolant temp sensor. So I've got 4 sensors. One is only for the rad fan. One is only for the gauge. I assumed one was only for the ECU, and the other was only for the EGR but maybe I'm wrong.
One of the last two has a green wire and a black wire and I can't find it in the schematics, so that's what I'm digging for now. Found it, it's the cold start injector. Basically a switch that's open above a certain temp and closed below it so power can pass through to the cold start injector. The other was like a red and brown I think, and I've tested it to be working at the ECU, ohm'ed out correctly for the temperature. It goes to pin THW on the ECU if that means anything.

sefiro
05-26-2016, 04:56 AM
Yes, the 4th sensor is for the cold start. May have to pull and test it in a pot of water on the stove. They are expensive - 130+

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Murgatroy
05-26-2016, 03:41 PM
Chaos has this same issue, when we swapped the engine at Bruce's it didn't have a cold start, and the thermostat housing was different. She didn't have room for a sensor, which was a coolant sensor. She throws a code for it. I was talking to Jeremy about it and I can't remember the exacts of the conversation, but he isn't certain that the missing temp sensor is causing her to dump fuel.

CollapsedNut
05-26-2016, 03:42 PM
Well I'm not using a cold start injector, nor any of the EGR system. So I really don't care if the cold start sensor works. The other one that goes to THW on the ecu I've already tested. So the ecu should be seeing temperature.

CollapsedNut
05-31-2016, 01:13 AM
Put the coolant hoses on my IACV, and put in a new O2 sensor. Seems to have fixed it. Never got any code for the O2 but I literally plugged in the new one and it was instant 14.7:1 afr idle. I guess the 165 IACV needs the coolant flow to work right, I was hoping to avoid that.