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Author Topic: High idle- IAC? Therm sensor?  (Read 579 times)

Offline 85GTSvert

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High idle- IAC? Therm sensor?
« on: Dec 24, 2018, 09:51:22 pm »
I’m dealing with a situation I’ve posted about before. I accidentally ran the car for a couple of miles without the oil cap, naturally splashing oil all over the engine bay, which gave rise to a high idle issue. I found my oil cap between the battery and the fender and drove back, but when I got to the first stop, I noticed I was idling at 2k rpms. Before, the idle was perfect. No running issues at all. I had to turn the idle screw all the way in to get to a 1k rpm warm idle. However, on a cold start, it will only idle at 5-600 rpms. It’s an auto, so with the torque converter applied while in gear, it drops even lower and will sometimes stall when going from R to D or giving it the first moderate bit of gas when leaving the neighborhood because of the low idle. Better than driving around idling at 2k when warm though. The idle itself is smooth. It has a very very slight up and down surge, but I need to dial in my new tps with my multi. I must have read 20 forum threads on various sites over the last few months and have concluded it may be either the IAC, the cold start switch, or the thermostat sensor next to it.

A noteworthy detail I should mention is that well before the oil cap incident, I had had the same low idle issue since I bought the car, but it fixed itself after I replaced the starter, fuel filter, and lower rad hose. I went to start the car but it wouldn’t turnover. I’m thinking wth?! I adjust the idle screw and the idle was perfect! I’m thinking draining the coolant did something to either the IAC or one of the two sensors and the oil cap incident has screwed it up again.

I took the IAC off today (car had sat overnight so it was cold), but I didn’t really know what I was doing. I had read that gasket sealer from a sloppy wster pump job will make its way through the coolant sustem to the IAC and clog the coolant nipples. I ran a pipe cleaner through it, but it didn’t look clogged nor did the pipe cleaner pull any crud out. One thing I did notice is that the plate inside was closed. I could see just a tiny hole in the plate. Shouldn’t it only be closed when the engine is warm? I’m afraid to take off the front cover with the 4 screws because they don’t make these IAC’s anymore or the square o ring style gasket for it.
« Last Edit: Dec 24, 2018, 10:02:47 pm by 85GTSvert »
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #1 on: Dec 26, 2018, 03:43:56 pm »
After sitting for a couple of days, I tested the cold injector time switch at 30 ohms and the thermostat sensor next to it at 3.2k ohms, if I’m reading the place holder scale correctly. The car was off at the time.

Anyone?
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline Teranfirbt

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Re: High idle- IAC? Therm sensor?
« Reply #2 on: Dec 26, 2018, 04:02:02 pm »
That's a tough one... Have you verified ignition timing with the correct jumper in place?
One possibility is that the oil somehow damaged the VSV for controlling AC idle up and its on all of the time, try plugging the small vacuum lines that go between the brass colored UFO on the side of the intake manifold to the vacuum valve on the valve cover. Don't loop the vacuum lines together, that will enable the AC idle up circuit.
1983 Celica GT-S 2RZ swap: Deered 2014 :(
1986 Tercel 4WD 4AFE Swap: Going strong
1986 MR2: What a beast!
2014 Elantra GT: The reliable one

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." ~ Albert Einstein

Offline Teranfirbt

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Re: High idle- IAC? Therm sensor?
« Reply #3 on: Dec 26, 2018, 04:06:47 pm »
What was the outside temp when you checked the sensor? That all sounds right. Have you tried blocking off the IAC supply to the intake to see if that is the issue?
1983 Celica GT-S 2RZ swap: Deered 2014 :(
1986 Tercel 4WD 4AFE Swap: Going strong
1986 MR2: What a beast!
2014 Elantra GT: The reliable one

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." ~ Albert Einstein

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #4 on: Dec 26, 2018, 04:39:16 pm »
Just tried plugging the two big IAC hoses and it won’t even run. I backed the idle adjustment screw out quite a lot, but nothing. Just turns over, revs once and dies.
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline Teranfirbt

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Re: High idle- IAC? Therm sensor?
« Reply #5 on: Dec 26, 2018, 04:57:53 pm »
Will it run with a bit of throttle?
1983 Celica GT-S 2RZ swap: Deered 2014 :(
1986 Tercel 4WD 4AFE Swap: Going strong
1986 MR2: What a beast!
2014 Elantra GT: The reliable one

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." ~ Albert Einstein

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #6 on: Dec 26, 2018, 06:03:07 pm »
Gah, forgot to plug the nipples on the upper intake. I capped off the iac but there was no change with it capped off. The engine was warm at this point.

One other symptom I noticed after the high idle issue returned is that it’s hesitant to shift into OD unless i’m going over 45 mph. Before, it would shift into OD over 35. Downshifts when slowing down seem to be firmer as I can hear my rear end clunk during some downshifts (it’s worn out, I have a low mileage spare).
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline Teranfirbt

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Re: High idle- IAC? Therm sensor?
« Reply #7 on: Dec 26, 2018, 08:11:07 pm »
OK, have you verified that the throttle is closing fully? I would verify that by pulling the air hose and making sure the throttle plate is fully closed in the housing.
1983 Celica GT-S 2RZ swap: Deered 2014 :(
1986 Tercel 4WD 4AFE Swap: Going strong
1986 MR2: What a beast!
2014 Elantra GT: The reliable one

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." ~ Albert Einstein

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #8 on: Dec 26, 2018, 08:57:27 pm »
Yep. Drum tight.
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline Teranfirbt

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Re: High idle- IAC? Therm sensor?
« Reply #9 on: Dec 26, 2018, 10:16:45 pm »
OK, so to verify, the engine still idles at 2000 with the IAC blocked off?
Have you verified ignition timing with the connector jumpered correctly?
Have you verified no vacuum leaks? Try disconnecting and capping the brake booster hose, could be the booster is damaged. Usually vacuum leaks make an engine run like crap, but if it's small enough that the O2 sensor can compensate then it might cause a high idle. Does your cruise control still work? Make sure it isn't doing anything silly like pulling on the throttle when it's off.
1983 Celica GT-S 2RZ swap: Deered 2014 :(
1986 Tercel 4WD 4AFE Swap: Going strong
1986 MR2: What a beast!
2014 Elantra GT: The reliable one

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." ~ Albert Einstein

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #10 on: Dec 27, 2018, 04:13:04 am »
Yes, the idle is still high, though it is adjusted down (maybe half a turn or a full turn from all the way in on the idle screw. Before the issue, the screw was somewhere in the middle of its range). I fiddled with the tps and the idle adjustment screw and the slight up and down surge is slightly better. I jumped the diagnostic port and it is throwing a code 7, which could mean a variety of faults, not necessarily a bad tps. Though there is no CEL unless in diagnostic mode.  Unfortunately, I don’t have a timing gun, so I have no way to verify by the book. I believe the brake booster hose is still original, so I will need to replace it, but all other hoses have been sorted, including all 4 hoses to the IAC. CC is disabled due to the nipple on the front of the CC motor being broken off by the PO. I will start it again tomorrow and squeeze the front hose, but yeah, I blocked off both air hoses going to the IAC and there was no change in response.

I started it on a semi cold start (after sitting for 30 mins) and it idled low at around 600 rpms and sputtered like it had a miss. I gave it some gas and held it at 1500 rpms for a few seconds and it was back to 1000 (more like 1100 where I have it now). Strange.

It takes a turn or two longer to start up with the issue, or I have to hold the revs up for a second or two before it evens out at 1000, otherwise it may idle at 600-800. Sometimes, it starts up and idles at 1000.  Before this issue, the starts were “strong” and it would literally take one or two turns to start. Fastest starting car I’ve owned. Chaw towt vs chaw towt towt towt. Lol

My next step is to spray some carb cleaner around all the hose attachments, test the resistance of the IAC, and maybe install my egr blockoff plates and bypass it.

Is the IAC circuit grounded through the intake, meaning do I have to have it bolted up in order to get the correct reading?
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

Offline 85GTSvert

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Re: High idle- IAC? Therm sensor?
« Reply #11 on: Jan 09, 2019, 03:31:28 am »
So, I deleted the egr and the 2k idle is gone. Obviously, the valve was stuck open and I was able to adjust the idle screw back to somewhere in the middle where it was prior to all of this. It still idles low on a cold start- around 800 rpms. Once fully at OT, its at 1k, where I set it. Also, on a warm start- after sitting for 15-30 mins, it idles a bit rough for the first minute. It almost sounds like a miss, but not as severe. I’m thinking of somehow finding a decent iac or converting to an 89-95 TB which uses a different iac. The only other issue is that when holding the revs in neutral anywhere between 1500-2000 rpms, it will give me erratic stumbles. Anywhere outside of that range, it’s fine and it doesn’t stumble in that range while driving/cruising.

I sprayed some brake cleaner around every vacuum hose connection, but didn’t notice any variation. Otherwise, after dialing in the tps and setting timing, it runs very well.
1985 Celica GT-S convertible- the popular one @ 264k mi
2002 Hyundai Santa Fe 2.7 V6- the semi-restored survivor @ 229k mi
2020 Hyundai Elantra GT N-Line 6-speed- not a GTI @ 38k mi

Yeah- I got a lot of toys. ‘85 GT-S bumpin’ Pet Shop Boys

 

cognitive