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High Idle When Hot 2003 Forester - Updated!

3207 Views 10 Replies 3 Participants Last post by  Brian Trauger, 
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This is my first time posting. I have a 2003 Forester that I have recently done some major repairs to. It all began with a blown radiator that caused an engine over heat and blown head gasket. All that has been repaired and the car is running great...except for the high idle when hot. I don't remember the car doing this before the head gasket failure - but the car had a cornucopia of problems before I decided to fix everything. After seeking advice from a mechanic friend I looked into the intake air temp sensor and the coolant temp sensor and both are giving normal readings according to my OBD II reader.

The symptom starts after the car is warmed up, intake air temp is 115 or higher and the coolant temp is 194 or higher, but it never reads above 202, and that high of a temp reading is only after the engine is idling high. The car does not have a MAF sensor and I have replaced the MAP sensor and the IAC (twice). I cleaned the intake and throttle body just to be sure there wasn't any buildup causing my problem. Nothing I have done seems to fix the problem. It also seems to go away if I turn the car off and let it sit for a short time - not long enough to fully cool down but enough to drop the intake temp reading a bit. The throttle position sensor is good, reading 0% when off the gas, even during the high idle scenario.

I'm not sure if this is a related issue to the high idle, but when I decelerate I get a minor backfire. The fuel trims seem normal (mostly close to 0) but I have seen the STFT spike to 70 on the positive several times while watching the live data as I drive, that doesn't seem to correlate to the backfire though. I have checked for vacuum leaks and haven't found any (I might have one that I can't diagnose but I would think that would cause erratic idle at all temperatures, not just when the engine is hot).

Is there any chance this could be a symptom of clogged or failing fuel injectors? I'm at a loss trying to solve this issue - everything I read says it should be the IAC, throttle body, vacuum leak, or MAF (which I don't have). The O2 sensors and whole exhaust system is new. The fuel injectors might be original, I am not aware of them ever being replaced - or cleaned. The car has 277,500 miles on it. I also have a P0442 small evap leak code. I have replaced the fuel filler neck, fuel cap (OEM), charcoal canister, vent valve, and purge solenoid - hasn't fixed the issue. Could this in any way be connected to the high idle issue? (BTW is there supposed to be a gasket between the filler neck and the "roll over/shut off valve")? I hate the idea of dropping the fuel tank to access the last bit of the evap system. I haven't found a local shop with a working smoke machine - hence my guess and check method!

I'm hoping someone on here is familiar with this issue, TYIA!
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2.5x_sleeper
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@Brian Trauger I see this is your first forum post, so welcome to the forum from Oregon! :biggrin:

How high is the hot idle? :confused:

I don't have a solution for you, but attachment below is from the Subaru technical service document, '03-'04, nonturbo.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]

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Thanks for the help!
The idle creeps up from the normal 600rpm to sometimes as high as 2000. The intake air temp seems to trigger it, when it's below 114 deg F the idle is normal but the longer I sit in traffic, the hotter the intake air, so 115 and up the idle gets going faster. Hottest I've seen the intake air is 135 deg and that was coupled with the coolant temp reading at 202 idle around 1800. The ambient air temp that day was over 100 so nothing about those numbers really stuck out to me other than the idle speed.

Looking at the chart you provided I have replaced the IAC and MAP sensor, checked the readings on both the coolant and intake air temperature sensors which appear normal and I have checked the throttle cable. Nothing seems to correct the issue. I'm wondering if it could be related to the P0457 code somehow?
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2.5x_sleeper
As to the P0457, take a look at thsi thread: Help evap codes!!!

Back to the idle issue. Does the radiator cool fans operate normally, as in, no overheating? :confused:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
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Thanks again Bobby. I'll have to check that the fans kick on without running the AC, I checked them earlier but only with the AC running. As for the evap code I'm going to have to drive to a place an hour away to get the smoke test done. The lines look good, wires/connectors good so I'm guessing it's something I can't see. I'm hoping that will solve my issue - maybe two birds with one stone? I'm not sure how evap could be related to high hot idle but a man can hope :smile2:
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R
I know raising the idle is a way your calibration can combat heat - I believe the reasoning is the water pump is more effective, and back when we had mechanical fans, it would be more effective as well. I've written a few calibrations but never played with this detail because our temperatures never get nearly that high here....My point is, this might be designed in by Subaru and intentional.
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Thanks for your reply @RyanT I checked to see if my fans turned on w/o AC and they did. I understand high idle speed is a part of the design when the temp gets too high, I've read that before somewhere. I just replaced the timing belt/water pump when I did the head gaskets so I'm not thinking it's a water pump issue.
I tried really hard to replicate the issue today when I ran my errands. The 30 min drive to work did not cause it this morning. After 10 min to the store it idled high. Spent <5 min in the store, came out, started it up, not high idling. Then drove to another store, took maybe 10 min, high idle returned. Spent <5 min in that store, came out, started up, not high idling, drove home and did not happen again, even with AC on - despite the intake air temp being between 120 and 137. So I'm beginning to wonder more and more if it's connected to the EVAP leak...had the rear brake line replaced a while ago and wondering if they broke/cracked a line at or near the fuel tank. When I stop the car with excessively high idle it is sometimes rough to start again, but evens out after it gets going (2-3 seconds), which also speaks to a temporary vacuum leak. I'm getting a smoke test done Monday morning. I'll update again after that. I really hope the repair won't involve dropping the fuel tank...not really feeling that.
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2.5x_sleeper
@Brian Trauger I was leaning towards the ECM not "sensing" the coolant temperature... as in, the ECM thinks the coolant temperature is low, cold & sets the idle high. Like on a cold start.
Since this didn't happen today, then that could still be a possibility... :confused:

Note that the coolant temperature sensor has 2 outputs. One goes to the ECM & the other one goes to the combination meter for the coolant gauge.

I'm going to say... guess that the P0457 is not causing the high idle.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
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I solved the high idle issue...I attempted to tap on the IAC and TPS just to see if they were defective, well in doing that I tapped the throttle cable connection (also where the CC connects) and the idle returned to normal. I got back in the driver seat, stepped on the gas and let up lightly, idle remained high, tapped the throttle cable, went back to normal. Turns out the return spring was filthy, a little cleaning and some lubricant and it's just fine now. I should have stuck to the KISS principle and I would have some extra $$ in my pocket since the IAC likely didn't need to be replaced at all!

Update on the P0457...I'm currently at a shop getting a smoke test done, typing this while I wait.
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2.5x_sleeper
@Brian Trauger thank you for updating your thread! I'll add "Updated!" to your thread title.

If you can add updates to your P0442... or P0457 issue on this thread or start a new thread. :wink:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
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Updated: P0457

Okay, so here's what I got from the $107 smoke test: "Charcoal canister w/vent valve" meaning tech says my new canister is leaking:|. He said there is a valve inside that is leaking? There are 3 hoses connected to the charcoal canister, no electronics. Does anyone here know if there is a check valve or something that could be defective with my canister? He seemed a little offended that I was questioning him but if I've learned anything, I've learned to "trust no one." :wink2: He said he was able to verify that the issue is the canister with his scan tool, I don't have an expensive one, is that possible to do?

Can anyone here verify that this could be a possibility? Can I check my canister and if so, how? I know some have the purge valve inside but it's separate on an '03...and I replaced that too.

Tech did confirm that he could not see any smoke leaks and he checked the valve on the gas tank with a vacuum so not that 0:)

Pic attached is of the paperwork. They gave me 60 days if I replace the canister and the CEL comes back on with same code to re-do the smoke test NC :smile2:

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